Max reported the following bug:
$ ./qemu-img create -f raw src.img 1G
$ ./qemu-img create -f raw dst.img 1G
$ (echo '
{"execute":"qmp_capabilities"}
{"execute":"blockdev-mirror",
"arguments":{"job-id":"mirror",
"device":"source",
"target":"target",
"sync":"full",
"filter-node-name":"mirror-top"}}
'; sleep 3; echo '
{"execute":"human-monitor-command",
"arguments":{"command-line":
"qemu-io mirror-top \"write 0 1G\""}}') \
| x86_64-softmmu/qemu-system-x86_64 \
-qmp stdio \
-blockdev file,node-name=source,filename=src.img \
-blockdev file,node-name=target,filename=dst.img \
-object iothread,id=iothr0 \
-device virtio-blk,drive=source,iothread=iothr0
crashes:
0 raise () at /usr/lib/libc.so.6
1 abort () at /usr/lib/libc.so.6
2 error_exit
(err=<optimized out>,
msg=msg@entry=0x55fbb1634790 <__func__.27> "qemu_mutex_unlock_impl")
at ../util/qemu-thread-posix.c:37
3 qemu_mutex_unlock_impl
(mutex=mutex@entry=0x55fbb25ab6e0,
file=file@entry=0x55fbb1636957 "../util/async.c",
line=line@entry=650)
at ../util/qemu-thread-posix.c:109
4 aio_context_release (ctx=ctx@entry=0x55fbb25ab680) at ../util/async.c:650
5 bdrv_do_drained_begin
(bs=bs@entry=0x55fbb3a87000, recursive=recursive@entry=false,
parent=parent@entry=0x0,
ignore_bds_parents=ignore_bds_parents@entry=false,
poll=poll@entry=true) at ../block/io.c:441
6 bdrv_do_drained_begin
(poll=true, ignore_bds_parents=false, parent=0x0, recursive=false,
bs=0x55fbb3a87000) at ../block/io.c:448
7 blk_drain (blk=0x55fbb26c5a00) at ../block/block-backend.c:1718
8 blk_unref (blk=0x55fbb26c5a00) at ../block/block-backend.c:498
9 blk_unref (blk=0x55fbb26c5a00) at ../block/block-backend.c:491
10 hmp_qemu_io (mon=0x7fffaf3fc7d0, qdict=<optimized out>)
at ../block/monitor/block-hmp-cmds.c:628
man pthread_mutex_unlock
...
EPERM The mutex type is PTHREAD_MUTEX_ERRORCHECK or
PTHREAD_MUTEX_RECURSIVE, or the mutex is a robust mutex, and the
current thread does not own the mutex.
So, thread doesn't own the mutex. And we have iothread here.
Next, note that AIO_WAIT_WHILE() documents that ctx must be acquired
exactly once by caller. But where is it acquired in the call stack?
Seems nowhere.
qemuio_command do acquire aio context.. But we need context acquired
around blk_unref() as well and actually around blk_insert_bs() too.
Let's refactor qemuio_command so that it doesn't acquire aio context
but callers do that instead. This way we can cleanly acquire aio
context in hmp_qemu_io() around all three calls.
Reported-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Message-Id: <20210423134233.51495-1-vsementsov@virtuozzo.com>
[mreitz: Fixed comment]
Signed-off-by: Max Reitz <mreitz@redhat.com>
78632a3d16