From 78632a3d1685454fec83f83586c675e7f2a1a84a Mon Sep 17 00:00:00 2001 From: Vladimir Sementsov-Ogievskiy Date: Fri, 23 Apr 2021 16:42:33 +0300 Subject: monitor: hmp_qemu_io: acquire aio contex, fix crash 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=, 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=) 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 Signed-off-by: Vladimir Sementsov-Ogievskiy Message-Id: <20210423134233.51495-1-vsementsov@virtuozzo.com> [mreitz: Fixed comment] Signed-off-by: Max Reitz --- block/monitor/block-hmp-cmds.c | 31 +++++++++++++++++++++---------- 1 file changed, 21 insertions(+), 10 deletions(-) (limited to 'block') diff --git a/block/monitor/block-hmp-cmds.c b/block/monitor/block-hmp-cmds.c index ebf1033f31..3e6670c963 100644 --- a/block/monitor/block-hmp-cmds.c +++ b/block/monitor/block-hmp-cmds.c @@ -557,8 +557,10 @@ void hmp_eject(Monitor *mon, const QDict *qdict) void hmp_qemu_io(Monitor *mon, const QDict *qdict) { - BlockBackend *blk; + BlockBackend *blk = NULL; + BlockDriverState *bs = NULL; BlockBackend *local_blk = NULL; + AioContext *ctx = NULL; 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"); @@ -573,20 +575,24 @@ void hmp_qemu_io(Monitor *mon, const QDict *qdict) } else { blk = blk_by_name(device); if (!blk) { - BlockDriverState *bs = bdrv_lookup_bs(NULL, device, &err); - if (bs) { - blk = local_blk = blk_new(bdrv_get_aio_context(bs), - 0, BLK_PERM_ALL); - ret = blk_insert_bs(blk, bs, &err); - if (ret < 0) { - goto fail; - } - } else { + bs = bdrv_lookup_bs(NULL, device, &err); + if (!bs) { goto fail; } } } + ctx = blk ? blk_get_aio_context(blk) : bdrv_get_aio_context(bs); + aio_context_acquire(ctx); + + if (bs) { + blk = local_blk = blk_new(bdrv_get_aio_context(bs), 0, BLK_PERM_ALL); + ret = blk_insert_bs(blk, bs, &err); + if (ret < 0) { + goto fail; + } + } + /* * Notably absent: Proper permission management. This is sad, but it seems * almost impossible to achieve without changing the semantics and thereby @@ -616,6 +622,11 @@ void hmp_qemu_io(Monitor *mon, const QDict *qdict) fail: blk_unref(local_blk); + + if (ctx) { + aio_context_release(ctx); + } + hmp_handle_error(mon, err); } -- cgit v1.2.3