btrfs: fix crash when trying to resume balance without the resume flag
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 filesystem:
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().
CC: stable@vger.kernel.org # 4.4+
Signed-off-by: Anand Jain <anand.jain@oracle.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 292266f..be3fc70 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -4052,6 +4052,15 @@ int btrfs_resume_balance_async(struct btrfs_fs_info *fs_info)
return 0;
}
+ /*
+ * A ro->rw remount sequence should continue with the paused balance
+ * regardless 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);
}