Backing may be zero after failed bdrv_attach_child in
bdrv_set_backing_hd, which leads to SIGSEGV.
Signed-off-by: Vladimir Sementsov-Ogievskiy <vsement...@virtuozzo.com>
---
Hi all.
We have faced into this SIGSEGV because of image locking:
trying to call qemu-img commit on locked image leads to the following:
Program terminated with signal 11, Segmentation fault.
#0 bdrv_mirror_top_refresh_filename (bs=0x5616df9a7400,
opts=0x5616df268400)
at block/mirror.c:1203
1203 bdrv_refresh_filename(bs->backing->bs);
(gdb) bt
#0 bdrv_mirror_top_refresh_filename (bs=0x5616df9a7400,
opts=0x5616df268400)
at block/mirror.c:1203
#1 0x00005616ddc3d35f in bdrv_refresh_filename (bs=0x5616df9a7400) at
block.c:4739
#2 0x00005616ddc3d672 in bdrv_set_backing_hd (bs=bs@entry=0x5616df9a7400,
backing_hd=backing_hd@entry=0x5616df25c000,
errp=errp@entry=0x7ffff7896a20)
at block.c:2035
#3 0x00005616ddc3dee3 in bdrv_append (bs_new=bs_new@entry=0x5616df9a7400,
bs_top=bs_top@entry=0x5616df25c000, errp=errp@entry=0x7ffff7896ad8)
at block.c:3168
#4 0x00005616ddc84e5f in mirror_start_job (
job_id=job_id@entry=0x5616ddd16a31 "commit",
bs=bs@entry=0x5616df25c000,
creation_flags=creation_flags@entry=0,
target=target@entry=0x5616df262800,
replaces=replaces@entry=0x0, speed=speed@entry=0, granularity=65536,
granularity@entry=0, buf_size=16777216, buf_size@entry=0,
backing_mode=backing_mode@entry=MIRROR_LEAVE_BACKING_CHAIN,
on_source_error=on_source_error@entry=BLOCKDEV_ON_ERROR_REPORT,
on_target_error=on_target_error@entry=BLOCKDEV_ON_ERROR_REPORT,
unmap=unmap@entry=true, cb=cb@entry=0x5616ddc35470
<common_block_job_cb>,
opaque=opaque@entry=0x7ffff7896c80, errp=errp@entry=0x7ffff7896bd0,
driver=driver@entry=0x5616ddf8d100 <commit_active_job_driver>,
is_none_mode=is_none_mode@entry=false, base=base@entry=0x5616df262800,
auto_complete=auto_complete@entry=false,
filter_node_name=filter_node_name@entry=0x0) at block/mirror.c:1314
#5 0x00005616ddc87580 in commit_active_start (
job_id=job_id@entry=0x5616ddd16a31 "commit",
bs=bs@entry=0x5616df25c000,
base=base@entry=0x5616df262800, creation_flags=creation_flags@entry=0,
speed=speed@entry=0, on_error=on_error@entry=BLOCKDEV_ON_ERROR_REPORT,
filter_node_name=filter_node_name@entry=0x0,
cb=cb@entry=0x5616ddc35470 <common_block_job_cb>,
opaque=opaque@entry=0x7ffff7896c80, errp=errp@entry=0x7ffff7896c78,
auto_complete=auto_complete@entry=false) at block/mirror.c:1463
#6 0x00005616ddc33a68 in img_commit (argc=<optimized out>, argv=<optimized
out>)
at qemu-img.c:1013
#7 0x00005616ddc2fa79 in main (argc=4, argv=0x7ffff7896e00) at
qemu-img.c:4548
(gdb) p bs->backing
$2 = (BdrvChild *) 0x0
(gdb) fr 2
#2 0x00005616ddc3d672 in bdrv_set_backing_hd (bs=bs@entry=0x5616df9a7400,
backing_hd=backing_hd@entry=0x5616df25c000,
errp=errp@entry=0x7ffff7896a20)
at block.c:2035
2035 bdrv_refresh_filename(bs);
(gdb) p *errp
$4 = (Error *) 0x5616df1c2660
(gdb) p **errp
$5 = {msg = 0x5616df2554e0 "Failed to get \"write\" lock",
err_class = ERROR_CLASS_GENERIC_ERROR,
src = 0x5616ddd267fe "block/file-posix.c",
func = 0x5616ddd26fe0 <__func__.27999> "raw_check_lock_bytes", line =
682,
hint = 0x5616df1fe520}
block/mirror.c | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/block/mirror.c b/block/mirror.c
index 6f5cb9f26c..351b80ca2c 100644
--- a/block/mirror.c
+++ b/block/mirror.c
@@ -1073,6 +1073,11 @@ static int coroutine_fn
bdrv_mirror_top_pdiscard(BlockDriverState *bs,
static void bdrv_mirror_top_refresh_filename(BlockDriverState *bs, QDict *opts)
{
+ if (bs->backing == NULL) {
+ /* we can be here after failed bdrv_attach_child in
+ * bdrv_set_backing_hd */
+ return;
+ }
bdrv_refresh_filename(bs->backing->bs);
pstrcpy(bs->exact_filename, sizeof(bs->exact_filename),
bs->backing->bs->filename);
--
2.11.1
