On 4/21/21 10:32 AM, Vladimir Sementsov-Ogievskiy wrote: > 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. Let's do it. > > Reported-by: Max Reitz <mre...@redhat.com> > Signed-off-by: Vladimir Sementsov-Ogievskiy <vsement...@virtuozzo.com> > --- > block/monitor/block-hmp-cmds.c | 7 +++++++ > 1 file changed, 7 insertions(+) > > diff --git a/block/monitor/block-hmp-cmds.c b/block/monitor/block-hmp-cmds.c > index ebf1033f31..934100d0eb 100644 > --- a/block/monitor/block-hmp-cmds.c > +++ b/block/monitor/block-hmp-cmds.c > @@ -559,6 +559,7 @@ void hmp_qemu_io(Monitor *mon, const QDict *qdict) > { > BlockBackend *blk; > BlockBackend *local_blk = NULL; > + AioContext *ctx; > bool qdev = qdict_get_try_bool(qdict, "qdev", false); > const char *device = qdict_get_str(qdict, "device"); > const char *command = qdict_get_str(qdict, "command"); > @@ -615,7 +616,13 @@ void hmp_qemu_io(Monitor *mon, const QDict *qdict) > qemuio_command(blk, command); > > fail: > + ctx = blk_get_aio_context(blk); > + aio_context_acquire(ctx); > + > blk_unref(local_blk); > + > + aio_context_release(ctx);
I dare to mention "code smell" here... Not to your fix, but to the API. Can't we simplify it somehow? Maybe we can't, I don't understand it well. But it seems bug prone, and expensive in human brain resources (either develop, debug or review). > hmp_handle_error(mon, err); > } > >