[dm-devel] [PATCH] Flush deferred queue when dm_suspend() is interrupted

[Jun'ichi Nomura]

Hello,

I found in a code review that dm_suspend() doesn't flush
deferred queue when it's interrupted and failed to suspend.

Attached patch theoretically fixes this problem.
But I don't have a testcase to pick this point
and would like to hear comment from others whether
there is something to prevent this.

Also, modifying DMF_BLOCK_IO outside of io_lock may
cause a race like this:
   CPU0 (dm_suspend)         CPU1 (dm_request)
   -------------------------------------------------
   set_bit(DMF_BLOCK_IO)
   ...
   up_write(io_lock)
                               down_read(io_lock)
                               test_bit(DMF_BLOCK_IO)
                               up_read(io_lock)
                               queue_io(deferred)
                                 down_write(io_lock)
                                 test_bit(DMF_BLOCK_IO)
                                 up_write(io_lock)
   clear_bit(DMF_BLOCK_IO)

   The deferred I/O never be flushed until dm_resume().


For the failed dm_suspend() case, there is another problem
that presuspend is not reverted.
It may require a new method like suspend_cancel() for
any target which implements presuspend().

I would appreicate a comment for this as well.

Thanks,
-- 
Jun'ichi Nomura, NEC Solutions (America), Inc.
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