• Vasiliy Kulikov's avatar
    ipc: introduce shm_rmid_forced sysctl · b34a6b1d
    Vasiliy Kulikov authored
    Add support for the shm_rmid_forced sysctl.  If set to 1, all shared
    memory objects in current ipc namespace will be automatically forced to
    use IPC_RMID.
    
    The POSIX way of handling shmem allows one to create shm objects and
    call shmdt(), leaving shm object associated with no process, thus
    consuming memory not counted via rlimits.
    
    With shm_rmid_forced=1 the shared memory object is counted at least for
    one process, so OOM killer may effectively kill the fat process holding
    the shared memory.
    
    It obviously breaks POSIX - some programs relying on the feature would
    stop working.  So set shm_rmid_forced=1 only if you're sure nobody uses
    "orphaned" memory.  Use shm_rmid_forced=0 by default for compatability
    reasons.
    
    The feature was previously impemented in -ow as a configure option.
    
    [akpm@linux-foundation.org: fix documentation, per Randy]
    [akpm@linux-foundation.org: fix warning]
    [akpm@linux-foundation.org: readability/conventionality tweaks]
    [akpm@linux-foundation.org: fix shm_rmid_forced/shm_forced_rmid confusion, use standard comment layout]
    Signed-off-by: default avatarVasiliy Kulikov <segoon@openwall.com>
    Cc: Randy Dunlap <rdunlap@xenotime.net>
    Cc: "Eric W. Biederman" <ebiederm@xmission.com>
    Cc: "Serge E. Hallyn" <serge.hallyn@canonical.com>
    Cc: Daniel Lezcano <daniel.lezcano@free.fr>
    Cc: Oleg Nesterov <oleg@redhat.com>
    Cc: Tejun Heo <tj@kernel.org>
    Cc: Ingo Molnar <mingo@elte.hu>
    Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
    Cc: Solar Designer <solar@openwall.com>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    b34a6b1d
ipc_namespace.h 3.7 KB