• Waiman Long's avatar
    locking/percpu-rwsem: Annotate rwsem ownership transfer by setting RWSEM_OWNER_UNKNOWN · 5a817641
    Waiman Long authored
    The filesystem freezing code needs to transfer ownership of a rwsem
    embedded in a percpu-rwsem from the task that does the freezing to
    another one that does the thawing by calling percpu_rwsem_release()
    after freezing and percpu_rwsem_acquire() before thawing.
    
    However, the new rwsem debug code runs afoul with this scheme by warning
    that the task that releases the rwsem isn't the one that acquires it,
    as reported by Amir Goldstein:
    
      DEBUG_LOCKS_WARN_ON(sem->owner != get_current())
      WARNING: CPU: 1 PID: 1401 at /home/amir/build/src/linux/kernel/locking/rwsem.c:133 up_write+0x59/0x79
    
      Call Trace:
       percpu_up_write+0x1f/0x28
       thaw_super_locked+0xdf/0x120
       do_vfs_ioctl+0x270/0x5f1
       ksys_ioctl+0x52/0x71
       __x64_sys_ioctl+0x16/0x19
       do_syscall_64+0x5d/0x167
       entry_SYSCALL_64_after_hwframe+0x49/0xbe
    
    To work properly with the rwsem debug code, we need to annotate that the
    rwsem ownership is unknown during the tranfer period until a brave soul
    comes forward to acquire the ownership. During that period, optimistic
    spinning will be disabled.
    Reported-by: Amir Goldstein's avatarAmir Goldstein <amir73il@gmail.com>
    Tested-by: Amir Goldstein's avatarAmir Goldstein <amir73il@gmail.com>
    Signed-off-by: Waiman Long's avatarWaiman Long <longman@redhat.com>
    Acked-by: default avatarPeter Zijlstra <peterz@infradead.org>
    Cc: Andrew Morton <akpm@linux-foundation.org>
    Cc: Davidlohr Bueso <dave@stgolabs.net>
    Cc: Jan Kara <jack@suse.cz>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Matthew Wilcox <willy@infradead.org>
    Cc: Oleg Nesterov <oleg@redhat.com>
    Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
    Cc: Theodore Y. Ts'o <tytso@mit.edu>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: Will Deacon <will.deacon@arm.com>
    Cc: linux-fsdevel@vger.kernel.org
    Link: http://lkml.kernel.org/r/1526420991-21213-3-git-send-email-longman@redhat.comSigned-off-by: default avatarIngo Molnar <mingo@kernel.org>
    5a817641
percpu-rwsem.h 4.09 KB