• Boqun Feng's avatar
    locking/lockdep: Explicitly initialize wq_barrier::done::map · 52fa5bc5
    Boqun Feng authored
    
    
    With the new lockdep crossrelease feature, which checks completions usage,
    a false positive is reported in the workqueue code:
    
    > Worker A : acquired of wfc.work -> wait for cpu_hotplug_lock to be released
    > Task   B : acquired of cpu_hotplug_lock -> wait for lock#3 to be released
    > Task   C : acquired of lock#3 -> wait for completion of barr->done
    > (Task C is in lru_add_drain_all_cpuslocked())
    > Worker D : wait for wfc.work to be released -> will complete barr->done
    
    Such a dead lock can not happen because Task C's barr->done and Worker D's
    barr->done can not be the same instance.
    
    The reason of this false positive is we initialize all wq_barrier::done
    at insert_wq_barrier() via init_completion(), which makes them belong to
    the same lock class, therefore, impossible circles are reported.
    
    To fix this, explicitly initialize the lockdep map for wq_barrier::done
    in insert_wq_barrier(), so that the lock class key of wq_barrier::done
    is a subkey of the corresponding work_struct, as a result we won't build
    a dependency between a wq_barrier with a unrelated work, and we can
    differ wq barriers based on the related works, so the false positive
    above is avoided.
    
    Also define the empty lockdep_init_map_crosslock() for !CROSSRELEASE
    to make the code simple and away from unnecessary #ifdefs.
    Reported-by: default avatarIngo Molnar <mingo@kernel.org>
    Signed-off-by: default avatarBoqun Feng <boqun.feng@gmail.com>
    Cc: Byungchul Park <byungchul.park@lge.com>
    Cc: Lai Jiangshan <jiangshanlai@gmail.com>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Tejun Heo <tj@kernel.org>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Link: http://lkml.kernel.org/r/20170817094622.12915-1-boqun.feng@gmail.com
    
    Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
    52fa5bc5
workqueue.c 156 KB