5.4-stable review patch. If anyone has any objections, please let me know.
------------------
From: xiaoshoukui <xiaoshoukui@xxxxxxxxx>
commit 29eefa6d0d07e185f7bfe9576f91e6dba98189c2 upstream.
Pausing and canceling balance can race to interrupt balance lead to BUG_ON
panic in btrfs_cancel_balance. The BUG_ON condition in btrfs_cancel_balance
does not take this race scenario into account.
However, the race condition has no other side effects. We can fix that.
Reproducing it with panic trace like this:
kernel BUG at fs/btrfs/volumes.c:4618!
RIP: 0010:btrfs_cancel_balance+0x5cf/0x6a0
Call Trace:
<TASK>
? do_nanosleep+0x60/0x120
? hrtimer_nanosleep+0xb7/0x1a0
? sched_core_clone_cookie+0x70/0x70
btrfs_ioctl_balance_ctl+0x55/0x70
btrfs_ioctl+0xa46/0xd20
__x64_sys_ioctl+0x7d/0xa0
do_syscall_64+0x38/0x80
entry_SYSCALL_64_after_hwframe+0x63/0xcd
Race scenario as follows:
> mutex_unlock(&fs_info->balance_mutex);
> --------------------
> .......issue pause and cancel req in another thread
> --------------------
> ret = __btrfs_balance(fs_info);
>
> mutex_lock(&fs_info->balance_mutex);
> if (ret == -ECANCELED && atomic_read(&fs_info->balance_pause_req)) {
> btrfs_info(fs_info, "balance: paused");
> btrfs_exclop_balance(fs_info, BTRFS_EXCLOP_BALANCE_PAUSED);
> }
CC: stable@xxxxxxxxxxxxxxx # 4.19+
Signed-off-by: xiaoshoukui <xiaoshoukui@xxxxxxxxxxxxx>
Reviewed-by: David Sterba <dsterba@xxxxxxxx>
Signed-off-by: David Sterba <dsterba@xxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
fs/btrfs/volumes.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -4558,8 +4558,7 @@ int btrfs_cancel_balance(struct btrfs_fs
}
}
- BUG_ON(fs_info->balance_ctl ||
- test_bit(BTRFS_FS_BALANCE_RUNNING, &fs_info->flags));
+ ASSERT(!test_bit(BTRFS_FS_BALANCE_RUNNING, &fs_info->flags));
atomic_dec(&fs_info->balance_cancel_req);
mutex_unlock(&fs_info->balance_mutex);
return 0;
