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=<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>
diff --git a/block/monitor/block-hmp-cmds.c b/block/monitor/block-hmp-cmds.c
index ebf1033..3e6670c 100644
--- a/block/monitor/block-hmp-cmds.c
+++ b/block/monitor/block-hmp-cmds.c
@@ -557,8 +557,10 @@
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 @@
} 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 @@
fail:
blk_unref(local_blk);
+
+ if (ctx) {
+ aio_context_release(ctx);
+ }
+
hmp_handle_error(mon, err);
}
diff --git a/qemu-io-cmds.c b/qemu-io-cmds.c
index 9761196..998b671 100644
--- a/qemu-io-cmds.c
+++ b/qemu-io-cmds.c
@@ -2457,9 +2457,12 @@
.oneline = "help for one or all commands",
};
+/*
+ * Called with aio context of blk acquired. Or with qemu_get_aio_context()
+ * context acquired if blk is NULL.
+ */
int qemuio_command(BlockBackend *blk, const char *cmd)
{
- AioContext *ctx;
char *input;
const cmdinfo_t *ct;
char **v;
@@ -2471,10 +2474,7 @@
if (c) {
ct = find_command(v[0]);
if (ct) {
- ctx = blk ? blk_get_aio_context(blk) : qemu_get_aio_context();
- aio_context_acquire(ctx);
ret = command(blk, ct, c, v);
- aio_context_release(ctx);
} else {
fprintf(stderr, "command \"%s\" not found\n", v[0]);
ret = -EINVAL;
diff --git a/qemu-io.c b/qemu-io.c
index bf90230..57f0750 100644
--- a/qemu-io.c
+++ b/qemu-io.c
@@ -411,6 +411,19 @@
*fetchable= 1;
}
+static int do_qemuio_command(const char *cmd)
+{
+ int ret;
+ AioContext *ctx =
+ qemuio_blk ? blk_get_aio_context(qemuio_blk) : qemu_get_aio_context();
+
+ aio_context_acquire(ctx);
+ ret = qemuio_command(qemuio_blk, cmd);
+ aio_context_release(ctx);
+
+ return ret;
+}
+
static int command_loop(void)
{
int i, fetchable = 0, prompted = 0;
@@ -418,7 +431,7 @@
char *input;
for (i = 0; !quit_qemu_io && i < ncmdline; i++) {
- ret = qemuio_command(qemuio_blk, cmdline[i]);
+ ret = do_qemuio_command(cmdline[i]);
if (ret < 0) {
last_error = ret;
}
@@ -446,7 +459,7 @@
if (input == NULL) {
break;
}
- ret = qemuio_command(qemuio_blk, input);
+ ret = do_qemuio_command(input);
g_free(input);
if (ret < 0) {
