Assume that the metadata of cow on the disk is corrupted after init
for some reason:
old chunk-id new chunk-id
0 2
...
x ---> 0 y
After starting merge, old chunk 0 will be updated twice, and old
chunk x will not be updated.
And dm-snap will print err log after merge new chunk 2 to old chunk 0:
<3>[ 731.921642] (1)[4092:kworker/1:0]device-mapper: snapshots:
Corruption detected: exception for block 0 is on disk but not in memory
then set snap->merge_failed to true.
If userspace use "sectors_allocated == metadata_sectors" to determine
whether the merge is completed, there maybe the following race that
makes the userspace unable to know merge fail event:
kernel merge kworker userspace process
merge_callback
->commit_merge
get snapshot_status by ioctl
->remove_single_exception_chunk
set merge_failed to true
think merge has been completed,
switch device to another target
Could we call remove_single_exception_chunk first to solve this race?
Signed-off-by: Jiazi.Li <jiazi.li@xxxxxxxxxxxxx>
---
drivers/md/dm-snap.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/drivers/md/dm-snap.c b/drivers/md/dm-snap.c
index f766c21408f1..f658d05752f2 100644
--- a/drivers/md/dm-snap.c
+++ b/drivers/md/dm-snap.c
@@ -1141,15 +1141,15 @@ static void merge_callback(int read_err, unsigned long write_err, void *context)
goto shut;
}
+ if (remove_single_exception_chunk(s) < 0)
+ goto shut;
+
if (s->store->type->commit_merge(s->store,
s->num_merging_chunks) < 0) {
DMERR("Write error in exception store: shutting down merge");
goto shut;
}
- if (remove_single_exception_chunk(s) < 0)
- goto shut;
-
snapshot_merge_next_chunks(s);
return;
--
2.17.1
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