[PATCH 5.19 644/717] btrfs: scrub: try to fix super block errors

Greg Kroah-Hartman
2022-10-22T08:48:40Z

From: Qu Wenruo <wqu@suse.com>

[ Upstream commit f9eab5f0bba76742af654f33d517bf62a0db8f12 ]

[BUG]
The following script shows that, although scrub can detect super block
errors, it never tries to fix it:

mkfs.btrfs -f -d raid1 -m raid1 $dev1 $dev2
xfs_io -c "pwrite 67108864 4k" $dev2

mount $dev1 $mnt
btrfs scrub start -B $dev2
btrfs scrub start -Br $dev2
umount $mnt

The first scrub reports the super error correctly:

scrub done for f3289218-abd3-41ac-a630-202f766c0859
Scrub started: Tue Aug 2 14:44:11 2022
Status: finished
Duration: 0:00:00
Total to scrub: 1.26GiB
Rate: 0.00B/s
Error summary: super=1
Corrected: 0
Uncorrectable: 0
Unverified: 0

But the second read-only scrub still reports the same super error:

Scrub started: Tue Aug 2 14:44:11 2022
Status: finished
Duration: 0:00:00
Total to scrub: 1.26GiB
Rate: 0.00B/s
Error summary: super=1
Corrected: 0
Uncorrectable: 0
Unverified: 0

[CAUSE]
The comments already shows that super block can be easily fixed by
committing a transaction:

/*
* If we find an error in a super block, we just report it.
* They will get written with the next transaction commit
* anyway
*/

But the truth is, such assumption is not always true, and since scrub
should try to repair every error it found (except for read-only scrub),
we should really actively commit a transaction to fix this.

[FIX]
Just commit a transaction if we found any super block errors, after
everything else is done.

We cannot do this just after scrub_supers(), as
btrfs_commit_transaction() will try to pause and wait for the running
scrub, thus we can not call it with scrub_lock hold.

Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/btrfs/scrub.c | 36 ++++++++++++++++++++++++++++++++++++
1 file changed, 36 insertions(+)

diff --git a/fs/btrfs/scrub.c b/fs/btrfs/scrub.c
index f62bfa023178..a14f97bf2a40 100644
--- a/fs/btrfs/scrub.c
+++ b/fs/btrfs/scrub.c
@@ -4112,6 +4112,7 @@ int btrfs_scrub_dev(struct btrfs_fs_info *fs_info, u64 devid, u64 start,
int ret;
struct btrfs_device *dev;
unsigned int nofs_flag;
+ bool need_commit = false;

if (btrfs_fs_closing(fs_info))
return -EAGAIN;
@@ -4215,6 +4216,12 @@ int btrfs_scrub_dev(struct btrfs_fs_info *fs_info, u64 devid, u64 start,
*/
nofs_flag = memalloc_nofs_save();
if (!is_dev_replace) {
+ u64 old_super_errors;
+
+ spin_lock(&sctx->stat_lock);
+ old_super_errors = sctx->stat.super_errors;
+ spin_unlock(&sctx->stat_lock);
+
btrfs_info(fs_info, "scrub: started on devid %llu", devid);
/*
* by holding device list mutex, we can
@@ -4223,6 +4230,16 @@ int btrfs_scrub_dev(struct btrfs_fs_info *fs_info, u64 devid, u64 start,
mutex_lock(&fs_info->fs_devices->device_list_mutex);
ret = scrub_supers(sctx, dev);
mutex_unlock(&fs_info->fs_devices->device_list_mutex);
+
+ spin_lock(&sctx->stat_lock);
+ /*
+ * Super block errors found, but we can not commit transaction
+ * at current context, since btrfs_commit_transaction() needs
+ * to pause the current running scrub (hold by ourselves).
+ */
+ if (sctx->stat.super_errors > old_super_errors && !sctx->readonly)
+ need_commit = true;
+ spin_unlock(&sctx->stat_lock);
}

if (!ret)
@@ -4249,6 +4266,25 @@ int btrfs_scrub_dev(struct btrfs_fs_info *fs_info, u64 devid, u64 start,
scrub_workers_put(fs_info);
scrub_put_ctx(sctx);

+ /*
+ * We found some super block errors before, now try to force a
+ * transaction commit, as scrub has finished.
+ */
+ if (need_commit) {
+ struct btrfs_trans_handle *trans;
+
+ trans = btrfs_start_transaction(fs_info->tree_root, 0);
+ if (IS_ERR(trans)) {
+ ret = PTR_ERR(trans);
+ btrfs_err(fs_info,
+ "scrub: failed to start transaction to fix super block errors: %d", ret);
+ return ret;
+ }
+ ret = btrfs_commit_transaction(trans);
+ if (ret < 0)
+ btrfs_err(fs_info,
+ "scrub: failed to commit transaction to fix super block errors: %d", ret);
+ }
return ret;
out:
scrub_workers_put(fs_info);
--
2.35.1