We set the BTRFS_BALANCE_RESUME flag in the btrfs_recover_balance()
only, which isn't called during the remount. So when resuming from
the paused balance we hit the BUG.
kernel: kernel BUG at fs/btrfs/volumes.c:3890!
::
kernel: balance_kthread+0x51/0x60 [btrfs]
kernel: kthread+0x111/0x130
::
kernel: RIP: btrfs_balance+0x12e1/0x1570 [btrfs] RSP: ffffba7d0090bde8
Reproducer:
On a mounted BTRFS.
btrfs balance start --full-balance /btrfs
btrfs balance pause /btrfs
mount -o remount,ro /dev/sdb /btrfs
mount -o remount,rw /dev/sdb /btrfs
To fix this set the BTRFS_BALANCE_RESUME flag in btrfs_resume_balance_async().
Signed-off-by: Anand Jain <anand.jain@xxxxxxxxxx>
---
v2->v3: . Hold fs_info->balance_lock because in remount context there can
be more the one thread accessing the balance_ctl.
. Don't remove the BTRFS_BALANCE_RESUME set at recover_balance
as in the original code.
. Add comments.
v1->v2: btrfs_resume_balance_async() can be called only from remount or
mount, we don't need to hold fs_info->balance_lock.
fs/btrfs/volumes.c | 9 +++++++++
1 file changed, 9 insertions(+)
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 40e4259bdd51..c68976856d87 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -4112,6 +4112,15 @@ int btrfs_resume_balance_async(struct btrfs_fs_info *fs_info)
return 0;
}
+ /*
+ * A remount ro->rw sequence should continue with the
+ * paused balance irrespective of who pauses it, system or
+ * the user as of now, so set the resume flag.
+ */
+ spin_lock(&fs_info->balance_lock);
+ fs_info->balance_ctl->flags |= BTRFS_BALANCE_RESUME;
+ spin_unlock(&fs_info->balance_lock);
+
tsk = kthread_run(balance_kthread, fs_info, "btrfs-balance");
return PTR_ERR_OR_ZERO(tsk);
}
--
2.7.0
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