• Jeff Moyer's avatar
    aio: wake up waiters when freeing unused kiocbs · 880641bb
    Jeff Moyer authored
    Bart Van Assche reported a hung fio process when either hot-removing
    storage or when interrupting the fio process itself.  The (pruned) call
    trace for the latter looks like so:
    
      fio             D 0000000000000001     0  6849   6848 0x00000004
       ffff880092541b88 0000000000000046 ffff880000000000 ffff88012fa11dc0
       ffff88012404be70 ffff880092541fd8 ffff880092541fd8 ffff880092541fd8
       ffff880128b894d0 ffff88012404be70 ffff880092541b88 000000018106f24d
      Call Trace:
        schedule+0x3f/0x60
        io_schedule+0x8f/0xd0
        wait_for_all_aios+0xc0/0x100
        exit_aio+0x55/0xc0
        mmput+0x2d/0x110
        exit_mm+0x10d/0x130
        do_exit+0x671/0x860
        do_group_exit+0x44/0xb0
        get_signal_to_deliver+0x218/0x5a0
        do_signal+0x65/0x700
        do_notify_resume+0x65/0x80
        int_signal+0x12/0x17
    
    The problem lies with the allocation batching code.  It will
    opportunistically allocate kiocbs, and then trim back the list of iocbs
    when there is not enough room in the completion ring to hold all of the
    events.
    
    In the case above, what happens is that the pruning back of events ends
    up freeing up the last active request and the context is marked as dead,
    so it is thus responsible for waking up waiters.  Unfortunately, the
    code does not check for this condition, so we end up with a hung task.
    Signed-off-by: default avatarJeff Moyer <jmoyer@redhat.com>
    Reported-by: default avatarBart Van Assche <bvanassche@acm.org>
    Tested-by: default avatarBart Van Assche <bvanassche@acm.org>
    Cc: <stable@kernel.org>		[3.2.x only]
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    880641bb
aio.c 48 KB