Am 29.11.2018 um 11:17 hat Vladimir Sementsov-Ogievskiy geschrieben: > Hi all! > > v2: add fix:) > > We've faced the following mirror bug: > > Just run mirror on qcow2 image more than 1G, and qemu is in dead lock. > > Dead lock described in 01, in short, we have extra aio_context_acquire > and aio_context_release around blk_aio_pwritev in mirror_read_complete. > So, write may yield to the main loop, and aio context is acquired. Main > loop than hangs on trying to lock BQL, which is locked by cpu thread, > and the cpu thread hangs on trying to acquire aio context. > > Hm, now the thing looks fixed, by I still have a questions: > > Is it a common thing, that we can't yield inside > aio_context_acquire/release ? > > Was commit b9e413dd3756 > "block: explicitly acquire aiocontext in aio callbacks that need it" > wrong? Why it added these acquire/release, when it is written in > multiple-iothreads.txt, that "Side note: the best way to schedule a function > call across threads is to call aio_bh_schedule_oneshot(). No acquire/release > or locking is needed." > > Can someone in short describe, what BQL and aio context lock means, what they > protect, and haw they should cooperate?
Thanks, applied patch 1 to the block branch. (We'll use Max' v3 for the test case.) Kevin
