1. 20 Dec, 2012 40 commits
    • Jeff Layton's avatar
      vfs: fix readlinkat to retry on ESTALE · 7955119e
      Jeff Layton authored
      
      Signed-off-by: default avatarJeff Layton <jlayton@redhat.com>
      Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
      7955119e
    • Jeff Layton's avatar
    • Jeff Layton's avatar
      vfs: add a retry_estale helper function to handle retries on ESTALE · b9d6ba94
      Jeff Layton authored
      
      
      This function is expected to be called from path-based syscalls to help
      them decide whether to try the lookup and call again in the event that
      they got an -ESTALE return back on an earier try.
      
      Currently, we only retry the call once on an ESTALE error, but in the
      event that we decide that that's not enough in the future, we should be
      able to change the logic in this helper without too much effort.
      Signed-off-by: default avatarJeff Layton <jlayton@redhat.com>
      Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
      b9d6ba94
    • Al Viro's avatar
      Merge branch 'fscache' of... · 21e89c0c
      Al Viro authored
      Merge branch 'fscache' of git://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs into for-linus
      21e89c0c
    • NeilBrown's avatar
      vfs: d_obtain_alias() needs to use "/" as default name. · b911a6bd
      NeilBrown authored
      
      
      NFS appears to use d_obtain_alias() to create the root dentry rather than
      d_make_root.  This can cause 'prepend_path()' to complain that the root
      has a weird name if an NFS filesystem is lazily unmounted.  e.g.  if
      "/mnt" is an NFS mount then
      
       { cd /mnt; umount -l /mnt ; ls -l /proc/self/cwd; }
      
      will cause a WARN message like
         WARNING: at /home/git/linux/fs/dcache.c:2624 prepend_path+0x1d7/0x1e0()
         ...
         Root dentry has weird name <>
      
      to appear in kernel logs.
      
      So change d_obtain_alias() to use "/" rather than "" as the anonymous
      name.
      Signed-off-by: default avatarNeilBrown <neilb@suse.de>
      Cc: Trond Myklebust <Trond.Myklebust@netapp.com>
      Cc: Al Viro <viro@zeniv.linux.org.uk>
      Cc: <stable@vger.kernel.org>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
      b911a6bd
    • Alessio Igor Bogani's avatar
      vfs: Remove useless function prototypes · 47166739
      Alessio Igor Bogani authored
      Commit 8e22cc88
      
       removes the (un)lock_super
      function definitions but forgets to remove their prototypes.
      Signed-off-by: default avatarAlessio Igor Bogani <abogani@kernel.org>
      Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
      47166739
    • Marco Stornelli's avatar
      documentation: drop vmtruncate · b9f61c3c
      Marco Stornelli authored
      
      
      Removed vmtruncate
      Signed-off-by: default avatarMarco Stornelli <marco.stornelli@gmail.com>
      Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
      b9f61c3c
    • Marco Stornelli's avatar
      mm: drop vmtruncate · 7898575f
      Marco Stornelli authored
      
      
      Removed vmtruncate
      Signed-off-by: default avatarMarco Stornelli <marco.stornelli@gmail.com>
      Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
      7898575f
    • Marco Stornelli's avatar
      vfs: drop vmtruncate · d30357f2
      Marco Stornelli authored
      
      
      Removed vmtruncate
      Signed-off-by: default avatarMarco Stornelli <marco.stornelli@gmail.com>
      Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
      d30357f2
    • Marco Stornelli's avatar
      ntfs: drop vmtruncate · 9014da75
      Marco Stornelli authored
      
      
      Removed vmtruncate
      Signed-off-by: default avatarMarco Stornelli <marco.stornelli@gmail.com>
      Reviewed-by: default avatarAnton Altaparmakov <anton@tuxera.com>
      Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
      9014da75
    • Marco Stornelli's avatar
      nilfs2: drop vmtruncate · 2d1b399b
      Marco Stornelli authored
      
      
      Removed vmtruncate
      Signed-off-by: default avatarMarco Stornelli <marco.stornelli@gmail.com>
      Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
      2d1b399b
    • Marco Stornelli's avatar
      ncpfs: drop vmtruncate · 3e7a8069
      Marco Stornelli authored
      
      
      Removed vmtruncate
      Signed-off-by: default avatarMarco Stornelli <marco.stornelli@gmail.com>
      Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
      3e7a8069
    • Marco Stornelli's avatar
      minix: drop vmtruncate · 7fc7cd00
      Marco Stornelli authored
      
      
      Removed vmtruncate
      Signed-off-by: default avatarMarco Stornelli <marco.stornelli@gmail.com>
      Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
      7fc7cd00
    • Marco Stornelli's avatar
      logfs: drop vmtruncate · 5dfc2821
      Marco Stornelli authored
      
      
      Removed vmtruncate
      Signed-off-by: default avatarMarco Stornelli <marco.stornelli@gmail.com>
      Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
      5dfc2821
    • Marco Stornelli's avatar
      hfsplus: drop vmtruncate · d5068485
      Marco Stornelli authored
      
      
      Removed vmtruncate
      Signed-off-by: default avatarMarco Stornelli <marco.stornelli@gmail.com>
      Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
      d5068485
    • Marco Stornelli's avatar
      jfs: drop vmtruncate · 86dd07d6
      Marco Stornelli authored
      
      
      Removed vmtruncate
      Signed-off-by: default avatarMarco Stornelli <marco.stornelli@gmail.com>
      Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
      86dd07d6
    • Marco Stornelli's avatar
      hpfs: drop vmtruncate · 70b31c4c
      Marco Stornelli authored
      
      
      Removed vmtruncate
      Signed-off-by: default avatarMarco Stornelli <marco.stornelli@gmail.com>
      Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
      70b31c4c
    • David Howells's avatar
      FS-Cache: Clear remaining page count on retrieval cancellation · 91c7fbbf
      David Howells authored
      
      
      Provide fscache_cancel_op() with a pointer to a function it should invoke under
      lock if it cancels an operation.
      
      Use this to clear the remaining page count upon cancellation of a pending
      retrieval operation so that fscache_release_retrieval_op() doesn't get an
      assertion failure (see below).  This can happen when a signal occurs, say from
      CTRL-C being pressed during data retrieval.
      
      FS-Cache: Assertion failed
      3 == 0 is false
      ------------[ cut here ]------------
      kernel BUG at fs/fscache/page.c:237!
      invalid opcode: 0000 [#641] SMP
      Modules linked in: cachefiles(F) nfsv4(F) nfsv3(F) nfsv2(F) nfs(F) fscache(F) auth_rpcgss(F) nfs_acl(F) lockd(F) sunrpc(F)
      CPU 0
      Pid: 6075, comm: slurp-q Tainted: GF     D      3.7.0-rc8-fsdevel+ #411                  /DG965RY
      RIP: 0010:[<ffffffffa007f328>]  [<ffffffffa007f328>] fscache_release_retrieval_op+0x75/0xff [fscache]
      RSP: 0000:ffff88001c6d7988  EFLAGS: 00010296
      RAX: 000000000000000f RBX: ffff880014cdfe00 RCX: ffffffff6c102000
      RDX: ffffffff8102d1ad RSI: ffffffff6c102000 RDI: ffffffff8102d1d6
      RBP: ffff88001c6d7998 R08: 0000000000000002 R09: 0000000000000000
      R10: 0000000000000000 R11: 0000000000000000 R12: 00000000fffffe00
      R13: ffff88001c6d7ab4 R14: ffff88001a8638a0 R15: ffff88001552b190
      FS:  00007f877aaf0700(0000) GS:ffff88003bc00000(0000) knlGS:0000000000000000
      CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
      CR2: 00007fff11378fd2 CR3: 000000001c6c6000 CR4: 00000000000007f0
      DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
      DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
      Process slurp-q (pid: 6075, threadinfo ffff88001c6d6000, task ffff88001c6c4080)
      Stack:
       ffffffffa007ec07 ffff880014cdfe00 ffff88001c6d79c8 ffffffffa007db4d
       ffffffffa007ec07 ffff880014cdfe00 00000000fffffe00 ffff88001c6d7ab4
       ffff88001c6d7a38 ffffffffa008116d 0000000000000000 ffff88001c6c4080
      Call Trace:
       [<ffffffffa007ec07>] ? fscache_cancel_op+0x194/0x1cf [fscache]
       [<ffffffffa007db4d>] fscache_put_operation+0x135/0x2ed [fscache]
       [<ffffffffa007ec07>] ? fscache_cancel_op+0x194/0x1cf [fscache]
       [<ffffffffa008116d>] __fscache_read_or_alloc_pages+0x413/0x4bc [fscache]
       [<ffffffff810ac8ae>] ? __alloc_pages_nodemask+0x195/0x75c
       [<ffffffffa00aab0f>] __nfs_readpages_from_fscache+0x86/0x13d [nfs]
       [<ffffffffa00a5fe0>] nfs_readpages+0x186/0x1bd [nfs]
       [<ffffffff810d23c8>] ? alloc_pages_current+0xc7/0xe4
       [<ffffffff810a68b5>] ? __page_cache_alloc+0x84/0x91
       [<ffffffff810af912>] ? __do_page_cache_readahead+0xa6/0x2e0
       [<ffffffff810afaa3>] __do_page_cache_readahead+0x237/0x2e0
       [<ffffffff810af912>] ? __do_page_cache_readahead+0xa6/0x2e0
       [<ffffffff810afe3e>] ra_submit+0x1c/0x20
       [<ffffffff810b019b>] ondemand_readahead+0x359/0x382
       [<ffffffff810b0279>] page_cache_sync_readahead+0x38/0x3a
       [<ffffffff810a77b5>] generic_file_aio_read+0x26b/0x637
       [<ffffffffa00f1852>] ? nfs_mark_delegation_referenced+0xb/0xb [nfsv4]
       [<ffffffffa009cc85>] nfs_file_read+0xaa/0xcf [nfs]
       [<ffffffff810db5b3>] do_sync_read+0x91/0xd1
       [<ffffffff810dbb8b>] vfs_read+0x9b/0x144
       [<ffffffff810dbc78>] sys_read+0x44/0x75
       [<ffffffff81422892>] system_call_fastpath+0x16/0x1b
      Signed-off-by: default avatarDavid Howells <dhowells@redhat.com>
      91c7fbbf
    • David Howells's avatar
      FS-Cache: Mark cancellation of in-progress operation · 1f372dff
      David Howells authored
      
      
      Mark as cancelled an operation that is in progress rather than pending at the
      time it is cancelled, and call fscache_complete_op() to cancel an operation so
      that blocked ops can be started.
      Signed-off-by: default avatarDavid Howells <dhowells@redhat.com>
      1f372dff
    • David Howells's avatar
      FS-Cache: One of the write operation paths doesn't set the object state · 7ef001e9
      David Howells authored
      
      
      In fscache_write_op(), if the object is determined to have become inactive or
      to have lost its cookie, we don't move the operation state from in-progress,
      and so an assertion in fscache_put_operation() fails with an assertion (see
      below).
      
      Instrumenting fscache_op_work_func() indicates that it called
      fscache_write_op() before calling fscache_put_operation() - where the assertion
      failed.  The assertion at line 433 indicates that the operation state is
      IN_PROGRESS rather than being COMPLETE or CANCELLED.
      
      Instrumenting fscache_write_op() showed that it was being called on an object
      that had had its cookie removed and that this was due to relinquishment of the
      cookie by the netfs.  At this point fscache no longer has access to the pages
      of netfs data that were requested to be written, and so simply cancelling the
      operation is the thing to do.
      
      FS-Cache: Assertion failed
      3 == 5 is false
      ------------[ cut here ]------------
      kernel BUG at fs/fscache/operation.c:433!
      invalid opcode: 0000 [#1] SMP
      Modules linked in: cachefiles(F) nfsv4(F) nfsv3(F) nfsv2(F) nfs(F) fscache(F) auth_rpcgss(F) nfs_acl(F) lockd(F) sunrpc(F)
      CPU 0
      Pid: 1035, comm: kworker/u:3 Tainted: GF            3.7.0-rc8-fsdevel+ #411                  /DG965RY
      RIP: 0010:[<ffffffffa007db22>]  [<ffffffffa007db22>] fscache_put_operation+0x11a/0x2ed [fscache]
      RSP: 0018:ffff88003e32bcf8  EFLAGS: 00010296
      RAX: 000000000000000f RBX: ffff88001818eb78 RCX: ffffffff6c102000
      RDX: ffffffff8102d1ad RSI: ffffffff6c102000 RDI: ffffffff8102d1d6
      RBP: ffff88003e32bd18 R08: 0000000000000002 R09: 0000000000000000
      R10: 0000000000000000 R11: 0000000000000000 R12: ffffffffa00811da
      R13: 0000000000000001 R14: 0000000100625d26 R15: 0000000000000000
      FS:  0000000000000000(0000) GS:ffff88003bc00000(0000) knlGS:0000000000000000
      CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
      CR2: 00007fff7dd31c68 CR3: 000000003d730000 CR4: 00000000000007f0
      DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
      DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
      Process kworker/u:3 (pid: 1035, threadinfo ffff88003e32a000, task ffff88003bb38080)
      Stack:
       ffffffff8102d1ad ffff88001818eb78 ffffffffa00811da 0000000000000001
       ffff88003e32bd48 ffffffffa007f0ad ffff88001818eb78 ffffffff819583c0
       ffff88003df24e00 ffff88003882c3e0 ffff88003e32bde8 ffffffff81042de0
      Call Trace:
       [<ffffffff8102d1ad>] ? vprintk_emit+0x3c6/0x41a
       [<ffffffffa00811da>] ? __fscache_read_or_alloc_pages+0x4bc/0x4bc [fscache]
       [<ffffffffa007f0ad>] fscache_op_work_func+0xec/0x123 [fscache]
       [<ffffffff81042de0>] process_one_work+0x21c/0x3b0
       [<ffffffff81042d82>] ? process_one_work+0x1be/0x3b0
       [<ffffffffa007efc1>] ? fscache_operation_gc+0x23e/0x23e [fscache]
       [<ffffffff8104332e>] worker_thread+0x202/0x2df
       [<ffffffff8104312c>] ? rescuer_thread+0x18e/0x18e
       [<ffffffff81047c1c>] kthread+0xd0/0xd8
       [<ffffffff81421bfa>] ? _raw_spin_unlock_irq+0x29/0x3e
       [<ffffffff81047b4c>] ? __init_kthread_worker+0x55/0x55
       [<ffffffff814227ec>] ret_from_fork+0x7c/0xb0
       [<ffffffff81047b4c>] ? __init_kthread_worker+0x55/0x55
      Signed-off-by: default avatarDavid Howells <dhowells@redhat.com>
      7ef001e9
    • David Howells's avatar
      FS-Cache: Fix signal handling during waits · 9c04caa8
      David Howells authored
      
      
      wait_on_bit() with TASK_INTERRUPTIBLE returns 1 rather than a negative error
      code, so change what we check for.  This means that the signal handling in
      fscache_wait_for_retrieval_activation()  should now work properly.
      
      Without this, the following bug can be seen if CTRL-C is pressed during
      fscache read operation:
      
      FS-Cache: Assertion failed
      2 == 3 is false
      ------------[ cut here ]------------
      kernel BUG at fs/fscache/page.c:347!
      invalid opcode: 0000 [#1] SMP
      Modules linked in: cachefiles(F) nfsv4(F) nfsv3(F) nfsv2(F) nfs(F) fscache(F) auth_rpcgss(F) nfs_acl(F) lockd(F) sunrpc(F)
      CPU 1
      Pid: 15006, comm: slurp-q Tainted: GF            3.7.0-rc8-fsdevel+ #411                  /DG965RY
      RIP: 0010:[<ffffffffa007fcb4>]  [<ffffffffa007fcb4>] fscache_wait_for_retrieval_activation+0x167/0x177 [fscache]
      RSP: 0018:ffff88002a4c39a8  EFLAGS: 00010292
      RAX: 000000000000001a RBX: ffff88002d3dc158 RCX: 0000000000008685
      RDX: ffffffff8102ccd6 RSI: 0000000000000001 RDI: ffffffff8102d1d6
      RBP: ffff88002a4c39c8 R08: 0000000000000002 R09: 0000000000000000
      R10: ffffffff8163afa0 R11: ffff88003bd11900 R12: ffffffffa00868c8
      R13: ffff880028306458 R14: ffff88002d3dc1b0 R15: ffff88001372e538
      FS:  00007f17426a0700(0000) GS:ffff88003bd00000(0000) knlGS:0000000000000000
      CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
      CR2: 00007f1742494a44 CR3: 0000000031bd7000 CR4: 00000000000007e0
      DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
      DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
      Process slurp-q (pid: 15006, threadinfo ffff88002a4c2000, task ffff880023de3040)
      Stack:
       ffff88002d3dc158 ffff88001372e538 ffff88002a4c3ab4 ffff8800283064e0
       ffff88002a4c3a38 ffffffffa0080f6d 0000000000000000 ffff880023de3040
       ffff88002a4c3ac8 ffffffff810ac8ae ffff880028306458 ffff88002a4c3bc8
      Call Trace:
       [<ffffffffa0080f6d>] __fscache_read_or_alloc_pages+0x24f/0x4bc [fscache]
       [<ffffffff810ac8ae>] ? __alloc_pages_nodemask+0x195/0x75c
       [<ffffffffa00aab0f>] __nfs_readpages_from_fscache+0x86/0x13d [nfs]
       [<ffffffffa00a5fe0>] nfs_readpages+0x186/0x1bd [nfs]
       [<ffffffff810d23c8>] ? alloc_pages_current+0xc7/0xe4
       [<ffffffff810a68b5>] ? __page_cache_alloc+0x84/0x91
       [<ffffffff810af912>] ? __do_page_cache_readahead+0xa6/0x2e0
       [<ffffffff810afaa3>] __do_page_cache_readahead+0x237/0x2e0
       [<ffffffff810af912>] ? __do_page_cache_readahead+0xa6/0x2e0
       [<ffffffff810afe3e>] ra_submit+0x1c/0x20
       [<ffffffff810b019b>] ondemand_readahead+0x359/0x382
       [<ffffffff810b0279>] page_cache_sync_readahead+0x38/0x3a
       [<ffffffff810a77b5>] generic_file_aio_read+0x26b/0x637
       [<ffffffffa00f1852>] ? nfs_mark_delegation_referenced+0xb/0xb [nfsv4]
       [<ffffffffa009cc85>] nfs_file_read+0xaa/0xcf [nfs]
       [<ffffffff810db5b3>] do_sync_read+0x91/0xd1
       [<ffffffff810dbb8b>] vfs_read+0x9b/0x144
       [<ffffffff810dbc78>] sys_read+0x44/0x75
       [<ffffffff81422892>] system_call_fastpath+0x16/0x1b
      Signed-off-by: default avatarDavid Howells <dhowells@redhat.com>
      9c04caa8
    • David Howells's avatar
      NFS4: Open files for fscaching · a4ff1468
      David Howells authored
      
      
      nfs4_file_open() should open files for fscaching.
      Signed-off-by: default avatarDavid Howells <dhowells@redhat.com>
      a4ff1468
    • David Howells's avatar
      FS-Cache: Add transition to handle invalidate immediately after lookup · 96969521
      David Howells authored
      
      
      Add a missing transition to the FS-Cache object state machine to handle an
      invalidation event occuring between the back end completing the object lookup
      by calling fscache_obtained_object() (which moves to state OBJECT_AVAILABLE)
      and the backend returning to fscache_lookup_object() and thence to
      fscache_object_state_machine() which then does a goto lookup_transit to handle
      the transition - but lookup_transit doesn't handle EV_INVALIDATE.
      
      Without this, the following BUG can be logged:
      
      	FS-Cache: Unsupported event 2 [5/f7] in state OBJECT_AVAILABLE
      	------------[ cut here ]------------
      	kernel BUG at fs/fscache/object.c:357!
      
      Where event 2 is EV_INVALIDATE.
      Signed-off-by: default avatarDavid Howells <dhowells@redhat.com>
      96969521
    • David Howells's avatar
      NFS: nfs_migrate_page() does not wait for FS-Cache to finish with a page · 8c209ce7
      David Howells authored
      
      
      nfs_migrate_page() does not wait for FS-Cache to finish with a page, probably
      leading to the following bad-page-state:
      
       BUG: Bad page state in process python-bin  pfn:17d39b
       page:ffffea00053649e8 flags:004000000000100c count:0 mapcount:0 mapping:(null)
      index:38686 (Tainted: G    B      ---------------- )
       Pid: 31053, comm: python-bin Tainted: G    B      ----------------
      2.6.32-71.24.1.el6.x86_64 #1
       Call Trace:
       [<ffffffff8111bfe7>] bad_page+0x107/0x160
       [<ffffffff8111ee69>] free_hot_cold_page+0x1c9/0x220
       [<ffffffff8111ef19>] __pagevec_free+0x59/0xb0
       [<ffffffff8104b988>] ? flush_tlb_others_ipi+0x128/0x130
       [<ffffffff8112230c>] release_pages+0x21c/0x250
       [<ffffffff8115b92a>] ? remove_migration_pte+0x28a/0x2b0
       [<ffffffff8115f3f8>] ? mem_cgroup_get_reclaim_stat_from_page+0x18/0x70
       [<ffffffff81122687>] ____pagevec_lru_add+0x167/0x180
       [<ffffffff811226f8>] __lru_cache_add+0x58/0x70
       [<ffffffff81122731>] lru_cache_add_lru+0x21/0x40
       [<ffffffff81123f49>] putback_lru_page+0x69/0x100
       [<ffffffff8115c0bd>] migrate_pages+0x13d/0x5d0
       [<ffffffff81122687>] ? ____pagevec_lru_add+0x167/0x180
       [<ffffffff81152ab0>] ? compaction_alloc+0x0/0x370
       [<ffffffff8115255c>] compact_zone+0x4cc/0x600
       [<ffffffff8111cfac>] ? get_page_from_freelist+0x15c/0x820
       [<ffffffff810672f4>] ? check_preempt_wakeup+0x1c4/0x3c0
       [<ffffffff8115290e>] compact_zone_order+0x7e/0xb0
       [<ffffffff81152a49>] try_to_compact_pages+0x109/0x170
       [<ffffffff8111e94d>] __alloc_pages_nodemask+0x5ed/0x850
       [<ffffffff814c9136>] ? thread_return+0x4e/0x778
       [<ffffffff81150d43>] alloc_pages_vma+0x93/0x150
       [<ffffffff81167ea5>] do_huge_pmd_anonymous_page+0x135/0x340
       [<ffffffff814cb6f6>] ? rwsem_down_read_failed+0x26/0x30
       [<ffffffff81136755>] handle_mm_fault+0x245/0x2b0
       [<ffffffff814ce383>] do_page_fault+0x123/0x3a0
       [<ffffffff814cbdf5>] page_fault+0x25/0x30
      
      nfs_migrate_page() calls nfs_fscache_release_page() which doesn't actually wait
      - even if __GFP_WAIT is set.  The reason that doesn't wait is that
      fscache_maybe_release_page() might deadlock the allocator as the work threads
      writing to the cache may all end up sleeping on memory allocation.
      
      However, I wonder if that is actually a problem.  There are a number of things
      I can do to deal with this:
      
       (1) Make nfs_migrate_page() wait.
      
       (2) Make fscache_maybe_release_page() honour the __GFP_WAIT flag.
      
       (3) Set a timeout around the wait.
      
       (4) Make nfs_migrate_page() return an error if the page is still busy.
      
      For the moment, I'll select (2) and (4).
      Signed-off-by: default avatarDavid Howells <dhowells@redhat.com>
      Acked-by: default avatarJeff Layton <jlayton@redhat.com>
      8c209ce7
    • David Howells's avatar
      FS-Cache: Exclusive op submission can BUG if there's been an I/O error · 8d76349d
      David Howells authored
      
      
      The function to submit an exclusive op (fscache_submit_exclusive_op()) can BUG
      if there's been an I/O error because it may see the parent cache object in an
      unexpected state.  It should only BUG if there hasn't been an I/O error.
      
      In this case the problem was produced by remounting the cache partition to be
      R/O.  The EROFS state was detected and the cache was aborted, but not
      everything handled the aborting correctly.
      
      SysRq : Emergency Remount R/O
      EXT4-fs (sda6): re-mounted. Opts: (null)
      Emergency Remount complete
      CacheFiles: I/O Error: Failed to update xattr with error -30
      FS-Cache: Cache cachefiles stopped due to I/O error
      ------------[ cut here ]------------
      kernel BUG at fs/fscache/operation.c:128!
      invalid opcode: 0000 [#1] SMP 
      CPU 0 
      Modules linked in: cachefiles nfs fscache auth_rpcgss nfs_acl lockd sunrpc
      
      Pid: 6612, comm: kworker/u:2 Not tainted 3.1.0-rc8-fsdevel+ #1093                  /DG965RY
      RIP: 0010:[<ffffffffa00739c0>]  [<ffffffffa00739c0>] fscache_submit_exclusive_op+0x2ad/0x2c2 [fscache]
      RSP: 0018:ffff880000853d40  EFLAGS: 00010206
      RAX: ffff880038ac72a8 RBX: ffff8800181f2260 RCX: ffffffff81f2b2b0
      RDX: 0000000000000001 RSI: ffffffff8179a478 RDI: ffff8800181f2280
      RBP: ffff880000853d60 R08: 0000000000000002 R09: 0000000000000000
      R10: 0000000000000001 R11: 0000000000000001 R12: ffff880038ac7268
      R13: ffff8800181f2280 R14: ffff88003a359190 R15: 000000010122b162
      FS:  0000000000000000(0000) GS:ffff88003bc00000(0000) knlGS:0000000000000000
      CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
      CR2: 00000034cc4a77f0 CR3: 0000000010e96000 CR4: 00000000000006f0
      DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
      DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
      Process kworker/u:2 (pid: 6612, threadinfo ffff880000852000, task ffff880014c3c040)
      Stack:
       ffff8800181f2260 ffff8800181f2310 ffff880038ac7268 ffff8800181f2260
       ffff880000853dc0 ffffffffa0072375 ffff880037ecfe00 ffff88003a359198
       ffff880000853dc0 0000000000000246 0000000000000000 ffff88000a91d308
      Call Trace:
       [<ffffffffa0072375>] fscache_object_work_func+0x792/0xe65 [fscache]
       [<ffffffff81047e44>] process_one_work+0x1eb/0x37f
       [<ffffffff81047de6>] ? process_one_work+0x18d/0x37f
       [<ffffffffa0071be3>] ? fscache_enqueue_dependents+0xd8/0xd8 [fscache]
       [<ffffffff810482e4>] worker_thread+0x15a/0x21a
       [<ffffffff8104818a>] ? rescuer_thread+0x188/0x188
       [<ffffffff8104bf96>] kthread+0x7f/0x87
       [<ffffffff813ad6f4>] kernel_thread_helper+0x4/0x10
       [<ffffffff81026b98>] ? finish_task_switch+0x45/0xc0
       [<ffffffff813abd1d>] ? retint_restore_args+0xe/0xe
       [<ffffffff8104bf17>] ? __init_kthread_worker+0x53/0x53
       [<ffffffff813ad6f0>] ? gs_change+0xb/0xb
      Signed-off-by: default avatarDavid Howells <dhowells@redhat.com>
      8d76349d
    • David Howells's avatar
      FS-Cache: Limit the number of I/O error reports for a cache · 75bc4113
      David Howells authored
      
      
      Limit the number of I/O error reports for a cache to 1 to prevent massive
      amounts of noise.  After the first I/O error the cache is taken off line
      automatically, so must be restarted to resume caching.
      Signed-off-by: default avatarDavid Howells <dhowells@redhat.com>
      75bc4113
    • David Howells's avatar
      FS-Cache: Don't mask off the object event mask when printing it · c2d35bfe
      David Howells authored
      
      
      Don't mask off the object event mask when printing it.  That way it can be seen
      if threre are bits set that shouldn't be.
      Signed-off-by: default avatarDavid Howells <dhowells@redhat.com>
      c2d35bfe
    • David Howells's avatar
      FS-Cache: Initialise the object event mask with the calculated mask · 03acc4be
      David Howells authored
      
      
      Initialise the object event mask with the calculated mask rather than unmasking
      undefined events also.
      Signed-off-by: default avatarDavid Howells <dhowells@redhat.com>
      03acc4be
    • David Howells's avatar
      FS-Cache: Convert the object event ID #defines into an enum · 36a02de5
      David Howells authored
      
      
      Convert the fscache_object event IDs from #defines into an enum.  Also add an
      extra label to the enum to carry the event count and redefine the event mask
      in terms of that.
      Signed-off-by: default avatarDavid Howells <dhowells@redhat.com>
      36a02de5
    • David Howells's avatar
      CacheFiles: Add missing retrieval completions · b4cf1e08
      David Howells authored
      
      
      CacheFiles is missing some calls to fscache_retrieval_complete() in the error
      handling/collision paths of its reader functions.
      
      This can be seen by the following assertion tripping in fscache_put_operation()
      whereby the operation being destroyed is still in the in-progress state and has
      not been cancelled or completed:
      
      FS-Cache: Assertion failed
      3 == 5 is false
      ------------[ cut here ]------------
      kernel BUG at fs/fscache/operation.c:408!
      invalid opcode: 0000 [#1] SMP
      CPU 2
      Modules linked in: xfs ioatdma dca loop joydev evdev
      psmouse dcdbas pcspkr serio_raw i5000_edac edac_core i5k_amb shpchp
      pci_hotplug sg sr_mod]
      
      Pid: 8062, comm: httpd Not tainted 3.1.0-rc8 #1 Dell Inc. PowerEdge 1950/0DT097
      RIP: 0010:[<ffffffff81197b24>]  [<ffffffff81197b24>] fscache_put_operation+0x304/0x330
      RSP: 0018:ffff880062f739d8  EFLAGS: 00010296
      RAX: 0000000000000025 RBX: ffff8800c5122e84 RCX: ffffffff81ddf040
      RDX: 00000000ffffffff RSI: 0000000000000082 RDI: ffffffff81ddef30
      RBP: ffff880062f739f8 R08: 0000000000000005 R09: 0000000000000000
      R10: 0000000000000000 R11: 0000000000000003 R12: ffff8800c5122e40
      R13: ffff880037a2cd20 R14: ffff880087c7a058 R15: ffff880087c7a000
      FS:  00007f63dcf636e0(0000) GS:ffff88022fc80000(0000) knlGS:0000000000000000
      CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
      CR2: 00007f0c0a91f000 CR3: 0000000062ec2000 CR4: 00000000000006e0
      DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
      DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
      Process httpd (pid: 8062, threadinfo ffff880062f72000, task ffff880087e58000)
      Stack:
       ffff880062f73bf8 0000000000000000 ffff880062f73bf8 ffff880037a2cd20
       ffff880062f73a68 ffffffff8119aa7e ffff88006540e000 ffff880062f73ad4
       ffff88008e9a4308 ffff880037a2cd20 ffff880062f73a48 ffff8800c5122e40
      Call Trace:
       [<ffffffff8119aa7e>] __fscache_read_or_alloc_pages+0x1fe/0x530
       [<ffffffff81250780>] __nfs_readpages_from_fscache+0x70/0x1c0
       [<ffffffff8123142a>] nfs_readpages+0xca/0x1e0
       [<ffffffff815f3c06>] ? rpc_do_put_task+0x36/0x50
       [<ffffffff8122755b>] ? alloc_nfs_open_context+0x4b/0x110
       [<ffffffff815ecd1a>] ? rpc_call_sync+0x5a/0x70
       [<ffffffff810e7e9a>] __do_page_cache_readahead+0x1ca/0x270
       [<ffffffff810e7f61>] ra_submit+0x21/0x30
       [<ffffffff810e818d>] ondemand_readahead+0x11d/0x250
       [<ffffffff810e83b6>] page_cache_sync_readahead+0x36/0x60
       [<ffffffff810dffa4>] generic_file_aio_read+0x454/0x770
       [<ffffffff81224ce1>] nfs_file_read+0xe1/0x130
       [<ffffffff81121bd9>] do_sync_read+0xd9/0x120
       [<ffffffff8114088f>] ? mntput+0x1f/0x40
       [<ffffffff811238cb>] ? fput+0x1cb/0x260
       [<ffffffff81122938>] vfs_read+0xc8/0x180
       [<ffffffff81122af5>] sys_read+0x55/0x90
      Reported-by: default avatarMark Moseley <moseleymark@gmail.com>
      Signed-off-by: default avatarDavid Howells <dhowells@redhat.com>
      b4cf1e08
    • David Howells's avatar
      NFS: Use FS-Cache invalidation · de242c0b
      David Howells authored
      
      
      Use the new FS-Cache invalidation facility from NFS to deal with foreign
      changes being detected on the server rather than attempting to retire the old
      cookie and get a new one.
      
      The problem with the old method was that NFS did not wait for all outstanding
      storage and retrieval ops on the cache to complete.  There was no automatic
      wait between the calls to ->readpages() and calls to invalidate_inode_pages2()
      as the latter can only wait on locked pages that have been added to the
      pagecache (which they haven't yet on entry to ->readpages()).
      
      This was leading to oopses like the one below when an outstanding read got cut
      off from its cookie by a premature release.
      
      BUG: unable to handle kernel NULL pointer dereference at 00000000000000a8
      IP: [<ffffffffa0075118>] __fscache_read_or_alloc_pages+0x1dd/0x315 [fscache]
      PGD 15889067 PUD 15890067 PMD 0
      Oops: 0000 [#1] SMP
      CPU 0
      Modules linked in: cachefiles nfs fscache auth_rpcgss nfs_acl lockd sunrpc
      
      Pid: 4544, comm: tar Not tainted 3.1.0-rc4-fsdevel+ #1064                  /DG965RY
      RIP: 0010:[<ffffffffa0075118>]  [<ffffffffa0075118>] __fscache_read_or_alloc_pages+0x1dd/0x315 [fscache]
      RSP: 0018:ffff8800158799e8  EFLAGS: 00010246
      RAX: 0000000000000000 RBX: ffff8800070d41e0 RCX: ffff8800083dc1b0
      RDX: 0000000000000000 RSI: ffff880015879960 RDI: ffff88003e627b90
      RBP: ffff880015879a28 R08: 0000000000000002 R09: 0000000000000002
      R10: 0000000000000001 R11: ffff880015879950 R12: ffff880015879aa4
      R13: 0000000000000000 R14: ffff8800083dc158 R15: ffff880015879be8
      FS:  00007f671e9d87c0(0000) GS:ffff88003bc00000(0000) knlGS:0000000000000000
      CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
      CR2: 00000000000000a8 CR3: 000000001587f000 CR4: 00000000000006f0
      DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
      DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
      Process tar (pid: 4544, threadinfo ffff880015878000, task ffff880015875040)
      Stack:
       ffffffffa00b1759 ffff8800070dc158 ffff8800000213da ffff88002a286508
       ffff880015879aa4 ffff880015879be8 0000000000000001 ffff88002a2866e8
       ffff880015879a88 ffffffffa00b20be 00000000000200da ffff880015875040
      Call Trace:
       [<ffffffffa00b1759>] ? nfs_fscache_wait_bit+0xd/0xd [nfs]
       [<ffffffffa00b20be>] __nfs_readpages_from_fscache+0x7e/0x13f [nfs]
       [<ffffffff81095fe7>] ? __alloc_pages_nodemask+0x156/0x662
       [<ffffffffa0098763>] nfs_readpages+0xee/0x187 [nfs]
       [<ffffffff81098a5e>] __do_page_cache_readahead+0x1be/0x267
       [<ffffffff81098942>] ? __do_page_cache_readahead+0xa2/0x267
       [<ffffffff81098d7b>] ra_submit+0x1c/0x20
       [<ffffffff8109900a>] ondemand_readahead+0x28b/0x29a
       [<ffffffff810990ce>] page_cache_sync_readahead+0x38/0x3a
       [<ffffffff81091d8a>] generic_file_aio_read+0x2ab/0x67e
       [<ffffffffa008cfbe>] nfs_file_read+0xa4/0xc9 [nfs]
       [<ffffffff810c22c4>] do_sync_read+0xba/0xfa
       [<ffffffff810a62c9>] ? might_fault+0x4e/0x9e
       [<ffffffff81177a47>] ? security_file_permission+0x7b/0x84
       [<ffffffff810c25dd>] ? rw_verify_area+0xab/0xc8
       [<ffffffff810c29a4>] vfs_read+0xaa/0x13a
       [<ffffffff810c2a79>] sys_read+0x45/0x6c
       [<ffffffff813ac37b>] system_call_fastpath+0x16/0x1b
      Reported-by: default avatarMark Moseley <moseleymark@gmail.com>
      Signed-off-by: default avatarDavid Howells <dhowells@redhat.com>
      de242c0b
    • David Howells's avatar
      CacheFiles: Implement invalidation · 9dc8d9bf
      David Howells authored
      
      
      Implement invalidation for CacheFiles.  This is in two parts:
      
       (1) Provide an invalidation method (which just truncates the backing file).
      
       (2) Abort attempts to copy anything read from the backing file whilst
           invalidation is in progress.
      
      Question: CacheFiles uses truncation in a couple of places.  It has been using
      notify_change() rather than sys_truncate() or something similar.  This means
      it bypasses a bunch of checks and suchlike that it possibly should be making
      (security, file locking, lease breaking, vfsmount write).  Should it be using
      vfs_truncate() as added by a preceding patch or should it use notify_write()
      and assume that anyone poking around in the cache files on disk gets
      everything they deserve?
      Signed-off-by: default avatarDavid Howells <dhowells@redhat.com>
      9dc8d9bf
    • David Howells's avatar
      VFS: Make more complete truncate operation available to CacheFiles · a02de960
      David Howells authored
      
      
      Make a more complete truncate operation available to CacheFiles (including
      security checks and suchlike) so that it can use this to clear invalidated
      cache files.
      Signed-off-by: default avatarDavid Howells <dhowells@redhat.com>
      Acked-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
      a02de960
    • David Howells's avatar
      FS-Cache: Provide proper invalidation · ef778e7a
      David Howells authored
      
      
      Provide a proper invalidation method rather than relying on the netfs retiring
      the cookie it has and getting a new one.  The problem with this is that isn't
      easy for the netfs to make sure that it has completed/cancelled all its
      outstanding storage and retrieval operations on the cookie it is retiring.
      
      Instead, have the cache provide an invalidation method that will cancel or wait
      for all currently outstanding operations before invalidating the cache, and
      will cause new operations to queue up behind that.  Whilst invalidation is in
      progress, some requests will be rejected until the cache can stack a barrier on
      the operation queue to cause new operations to be deferred behind it.
      Signed-off-by: default avatarDavid Howells <dhowells@redhat.com>
      ef778e7a
    • David Howells's avatar
      FS-Cache: Fix operation state management and accounting · 9f10523f
      David Howells authored
      
      
      Fix the state management of internal fscache operations and the accounting of
      what operations are in what states.
      
      This is done by:
      
       (1) Give struct fscache_operation a enum variable that directly represents the
           state it's currently in, rather than spreading this knowledge over a bunch
           of flags, who's processing the operation at the moment and whether it is
           queued or not.
      
           This makes it easier to write assertions to check the state at various
           points and to prevent invalid state transitions.
      
       (2) Add an 'operation complete' state and supply a function to indicate the
           completion of an operation (fscache_op_complete()) and make things call
           it.  The final call to fscache_put_operation() can then check that an op
           in the appropriate state (complete or cancelled).
      
       (3) Adjust the use of object->n_ops, ->n_in_progress, ->n_exclusive to better
           govern the state of an object:
      
      	(a) The ->n_ops is now the number of extant operations on the object
      	    and is now decremented by fscache_put_operation() only.
      
      	(b) The ->n_in_progress is simply the number of objects that have been
      	    taken off of the object's pending queue for the purposes of being
      	    run.  This is decremented by fscache_op_complete() only.
      
      	(c) The ->n_exclusive is the number of exclusive ops that have been
      	    submitted and queued or are in progress.  It is decremented by
      	    fscache_op_complete() and by fscache_cancel_op().
      
           fscache_put_operation() and fscache_operation_gc() now no longer try to
           clean up ->n_exclusive and ->n_in_progress.  That was leading to double
           decrements against fscache_cancel_op().
      
           fscache_cancel_op() now no longer decrements ->n_ops.  That was leading to
           double decrements against fscache_put_operation().
      
           fscache_submit_exclusive_op() now decides whether it has to queue an op
           based on ->n_in_progress being > 0 rather than ->n_ops > 0 as the latter
           will persist in being true even after all preceding operations have been
           cancelled or completed.  Furthermore, if an object is active and there are
           runnable ops against it, there must be at least one op running.
      
       (4) Add a remaining-pages counter (n_pages) to struct fscache_retrieval and
           provide a function to record completion of the pages as they complete.
      
           When n_pages reaches 0, the operation is deemed to be complete and
           fscache_op_complete() is called.
      
           Add calls to fscache_retrieval_complete() anywhere we've finished with a
           page we've been given to read or allocate for.  This includes places where
           we just return pages to the netfs for reading from the server and where
           accessing the cache fails and we discard the proposed netfs page.
      
      The bugs in the unfixed state management manifest themselves as oopses like the
      following where the operation completion gets out of sync with return of the
      cookie by the netfs.  This is possible because the cache unlocks and returns
      all the netfs pages before recording its completion - which means that there's
      nothing to stop the netfs discarding them and returning the cookie.
      
      
      FS-Cache: Cookie 'NFS.fh' still has outstanding reads
      ------------[ cut here ]------------
      kernel BUG at fs/fscache/cookie.c:519!
      invalid opcode: 0000 [#1] SMP
      CPU 1
      Modules linked in: cachefiles nfs fscache auth_rpcgss nfs_acl lockd sunrpc
      
      Pid: 400, comm: kswapd0 Not tainted 3.1.0-rc7-fsdevel+ #1090                  /DG965RY
      RIP: 0010:[<ffffffffa007050a>]  [<ffffffffa007050a>] __fscache_relinquish_cookie+0x170/0x343 [fscache]
      RSP: 0018:ffff8800368cfb00  EFLAGS: 00010282
      RAX: 000000000000003c RBX: ffff880023cc8790 RCX: 0000000000000000
      RDX: 0000000000002f2e RSI: 0000000000000001 RDI: ffffffff813ab86c
      RBP: ffff8800368cfb50 R08: 0000000000000002 R09: 0000000000000000
      R10: ffff88003a1b7890 R11: ffff88001df6e488 R12: ffff880023d8ed98
      R13: ffff880023cc8798 R14: 0000000000000004 R15: ffff88003b8bf370
      FS:  0000000000000000(0000) GS:ffff88003bd00000(0000) knlGS:0000000000000000
      CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
      CR2: 00000000008ba008 CR3: 0000000023d93000 CR4: 00000000000006e0
      DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
      DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
      Process kswapd0 (pid: 400, threadinfo ffff8800368ce000, task ffff88003b8bf040)
      Stack:
       ffff88003b8bf040 ffff88001df6e528 ffff88001df6e528 ffffffffa00b46b0
       ffff88003b8bf040 ffff88001df6e488 ffff88001df6e620 ffffffffa00b46b0
       ffff88001ebd04c8 0000000000000004 ffff8800368cfb70 ffffffffa00b2c91
      Call Trace:
       [<ffffffffa00b2c91>] nfs_fscache_release_inode_cookie+0x3b/0x47 [nfs]
       [<ffffffffa008f25f>] nfs_clear_inode+0x3c/0x41 [nfs]
       [<ffffffffa0090df1>] nfs4_evict_inode+0x2f/0x33 [nfs]
       [<ffffffff810d8d47>] evict+0xa1/0x15c
       [<ffffffff810d8e2e>] dispose_list+0x2c/0x38
       [<ffffffff810d9ebd>] prune_icache_sb+0x28c/0x29b
       [<ffffffff810c56b7>] prune_super+0xd5/0x140
       [<ffffffff8109b615>] shrink_slab+0x102/0x1ab
       [<ffffffff8109d690>] balance_pgdat+0x2f2/0x595
       [<ffffffff8103e009>] ? process_timeout+0xb/0xb
       [<ffffffff8109dba3>] kswapd+0x270/0x289
       [<ffffffff8104c5ea>] ? __init_waitqueue_head+0x46/0x46
       [<ffffffff8109d933>] ? balance_pgdat+0x595/0x595
       [<ffffffff8104bf7a>] kthread+0x7f/0x87
       [<ffffffff813ad6b4>] kernel_thread_helper+0x4/0x10
       [<ffffffff81026b98>] ? finish_task_switch+0x45/0xc0
       [<ffffffff813abcdd>] ? retint_restore_args+0xe/0xe
       [<ffffffff8104befb>] ? __init_kthread_worker+0x53/0x53
       [<ffffffff813ad6b0>] ? gs_change+0xb/0xb
      Signed-off-by: default avatarDavid Howells <dhowells@redhat.com>
      9f10523f
    • David Howells's avatar
      FS-Cache: Make cookie relinquishment wait for outstanding reads · ef46ed88
      David Howells authored
      
      
      Make fscache_relinquish_cookie() log a warning and wait if there are any
      outstanding reads left on the cookie it was given.
      Signed-off-by: default avatarDavid Howells <dhowells@redhat.com>
      ef46ed88
    • David Howells's avatar
      CacheFiles: Make some debugging statements conditional · 37491a13
      David Howells authored
      
      
      Downgrade some debugging statements to not unconditionally print stuff, but
      rather be conditional on the appropriate module parameter setting.
      Signed-off-by: default avatarDavid Howells <dhowells@redhat.com>
      37491a13
    • David Howells's avatar
      FS-Cache: Check that there are no read ops when cookie relinquished · 0f972b56
      David Howells authored
      
      
      Check that the netfs isn't trying to relinquish a cookie that still has read
      operations in progress upon it.  If there are, then give log a warning and BUG.
      Signed-off-by: default avatarDavid Howells <dhowells@redhat.com>
      0f972b56
    • David Howells's avatar
      CacheFiles: Downgrade the requirements passed to the allocator · 5f4f9f4a
      David Howells authored
      
      
      Downgrade the requirements passed to the allocator in the gfp flags parameter.
      FS-Cache/CacheFiles can handle OOM conditions simply by aborting the attempt to
      store an object or a page in the cache.
      Signed-off-by: default avatarDavid Howells <dhowells@redhat.com>
      5f4f9f4a
    • David Howells's avatar
      CacheFiles: Fix the marking of cached pages · c4d6d8db
      David Howells authored
      
      
      Under some circumstances CacheFiles defers the marking of pages with PG_fscache
      so that it can take advantage of pagevecs to reduce the number of calls to
      fscache_mark_pages_cached() and the netfs's hook to keep track of this.
      
      There are, however, two problems with this:
      
       (1) It can lead to the PG_fscache mark being applied _after_ the page is set
           PG_uptodate and unlocked (by the call to fscache_end_io()).
      
       (2) CacheFiles's ref on the page is dropped immediately following
           fscache_end_io() - and so may not still be held when the mark is applied.
           This can lead to the page being passed back to the allocator before the
           mark is applied.
      
      Fix this by, where appropriate, marking the page before calling
      fscache_end_io() and releasing the page.  This means that we can't take
      advantage of pagevecs and have to make a separate call for each page to the
      marking routines.
      
      The symptoms of this are Bad Page state errors cropping up under memory
      pressure, for example:
      
      BUG: Bad page state in process tar  pfn:002da
      page:ffffea0000009fb0 count:0 mapcount:0 mapping:          (null) index:0x1447
      page flags: 0x1000(private_2)
      Pid: 4574, comm: tar Tainted: G        W   3.1.0-rc4-fsdevel+ #1064
      Call Trace:
       [<ffffffff8109583c>] ? dump_page+0xb9/0xbe
       [<ffffffff81095916>] bad_page+0xd5/0xea
       [<ffffffff81095d82>] get_page_from_freelist+0x35b/0x46a
       [<ffffffff810961f3>] __alloc_pages_nodemask+0x362/0x662
       [<ffffffff810989da>] __do_page_cache_readahead+0x13a/0x267
       [<ffffffff81098942>] ? __do_page_cache_readahead+0xa2/0x267
       [<ffffffff81098d7b>] ra_submit+0x1c/0x20
       [<ffffffff8109900a>] ondemand_readahead+0x28b/0x29a
       [<ffffffff81098ee2>] ? ondemand_readahead+0x163/0x29a
       [<ffffffff810990ce>] page_cache_sync_readahead+0x38/0x3a
       [<ffffffff81091d8a>] generic_file_aio_read+0x2ab/0x67e
       [<ffffffffa008cfbe>] nfs_file_read+0xa4/0xc9 [nfs]
       [<ffffffff810c22c4>] do_sync_read+0xba/0xfa
       [<ffffffff81177a47>] ? security_file_permission+0x7b/0x84
       [<ffffffff810c25dd>] ? rw_verify_area+0xab/0xc8
       [<ffffffff810c29a4>] vfs_read+0xaa/0x13a
       [<ffffffff810c2a79>] sys_read+0x45/0x6c
       [<ffffffff813ac37b>] system_call_fastpath+0x16/0x1b
      
      As can be seen, PG_private_2 (== PG_fscache) is set in the page flags.
      
      Instrumenting fscache_mark_pages_cached() to verify whether page->mapping was
      set appropriately showed that sometimes it wasn't.  This led to the discovery
      that sometimes the page has apparently been reclaimed by the time the marker
      got to see it.
      Reported-by: default avatarM. Stevens <m@tippett.com>
      Signed-off-by: default avatarDavid Howells <dhowells@redhat.com>
      Reviewed-by: default avatarJeff Layton <jlayton@redhat.com>
      c4d6d8db