[dm-devel] [PATCH] md: dm-verity: Fix to avoid a deadlock in dm-bufio
Paul Menzel
pm.debian at googlemail.com
Mon Mar 4 17:19:15 UTC 2013
Am Montag, den 04.03.2013, 08:45 -0800 schrieb Paul Taysom:
> Changed the dm-verity prefetching to use a worker thread to avoid
> a deadlock in dm-bufio.
Do you know of any bug reports about this? Searching for »dm-verity dead
lock« I found [1], which seems to be the issue, right? If yes, please
reference it.
> If generic_make_request is called recursively, it queues the I/O
> request on the current->bio_list without making the I/O request
> and returns. The routine making the recursive call cannot wait
> for the I/O to complete.
>
> The deadlock occurred when one thread grabbed the bufio_client
> mutex and waited for an I/O to complete but the I/O was queued
> on another thread’s current->bio_list and it was waiting to get
> the mutex held by the first thread.
>
> The fix allows only one I/O request from dm-verity to dm-bufio
> per thread. To do this, the prefetch requests were queued on worker
> threads.
>
> In addition to avoiding the deadlock, this fix made a slight
> improvement in performance.
>
> seconds_kernel_to_login:
> with prefetch: 8.43s
> without prefetch: 9.2s
> worker prefetch: 8.28s
>
> Signed-off-by: Paul Taysom <taysom at chromium.org>
> ---
> drivers/md/dm-verity.c | 29 +++++++++++++++++++++++++++--
> 1 file changed, 27 insertions(+), 2 deletions(-)
Acked-by: Paul Menzel <paulepanter at users.sourceforge.net>
Thanks,
Paul
[1] https://code.google.com/p/chromium-os/issues/detail?id=39148
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