Re: [Qemu-block] [Qemu-devel] [PATCH for 2.7 0/2] block: fixes for deadlock in flush code

[Stefan Hajnoczi]

On Wed, Aug 17, 2016 at 09:06:52PM +0300, Denis V. Lunev wrote:
> We have suffered from the following deadlock
> 
> Thread 2 (Thread 0x7f1b7edf9700 (LWP 240293)):
> #0  0x00007f1bd1f0675f in ppoll () from /lib64/libc.so.6
> #1  0x00007f1bd8c1d78b in ppoll (__ss=0x0, __timeout=0x0, __nfds=<optimized 
> out>, __fds=<optimized out>) at /usr/include/bits/poll2.h:77
> #2  qemu_poll_ns (fds=<optimized out>, nfds=<optimized out>, address@hidden) 
> at qemu-timer.c:310
> #3  0x00007f1bd8c1e8bf in aio_poll (ctx=0x7f1bda091780, address@hidden) at 
> aio-posix.c:451
> #4  0x00007f1bd8c119cf in bdrv_drain_one (address@hidden) at block.c:2055
> #5  0x00007f1bd8c13244 in bdrv_drain_all () at block.c:2115
> #6  0x00007f1bd8a2c5e3 in vm_stop (state=<optimized out>) at 
> /usr/src/debug/qemu-2.3.0/cpus.c:685
> #7  0x00007f1bd8a2c636 in vm_stop_force_state (state=<optimized out>) at 
> /usr/src/debug/qemu-2.3.0/cpus.c:1383
> #8  0x00007f1bd8bc798f in migration_completion (start_time=<synthetic 
> pointer>, old_vm_running=<synthetic pointer>, current_active_state=<optimized 
> out>, s=0x7f1bd90e3c20 <current_migration.37255>)
>         at migration/migration.c:1213
> #9  migration_thread (opaque=0x7f1bd90e3c20 <current_migration.37255>) at 
> migration/migration.c:1314
> #10 0x00007f1bd21e3dc5 in start_thread () from /lib64/libpthread.so.0
> #11 0x00007f1bd1f10ced in clone () from /lib64/libc.so.6
> 
> The problem was narrowed down to the commit
>     commit 3ff2f67a7c24183fcbcfe1332e5223ac6f96438c
>     Author: Evgeny Yakovlev <address@hidden>
>     Date:   Mon Jul 18 22:39:52 2016 +0300
>     block: ignore flush requests when storage is clean
> 
> This patches contains fixes for the situation. The probability of the
> problem is not that big. Our regression testing faces it ~1 time
> a week or less.
> 
> Signed-off-by: Evgeny Yakovlev <address@hidden>
> Signed-off-by: Denis V. Lunev <address@hidden>
> CC: Stefan Hajnoczi <address@hidden>
> CC: Fam Zheng <address@hidden>
> CC: Kevin Wolf <address@hidden>
> CC: Max Reitz <address@hidden>
> 
> 

Thanks, applied to my block tree:
https://github.com/stefanha/qemu/commits/block

Stefan

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