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Message-Id: <20230815065559.31546-1-xiaoshoukui@gmail.com>
Date: Tue, 15 Aug 2023 02:55:59 -0400
From: xiaoshoukui <xiaoshoukui@...il.com>
To: clm@...com, josef@...icpanda.com, dsterba@...e.com
Cc: linux-btrfs@...r.kernel.org, linux-kernel@...r.kernel.org,
xiaoshoukui <xiaoshoukui@...jie.com.cn>
Subject: [PATCH] btrfs: fix BUG_ON condition in btrfs_cancel_balance
Pausing and canceling balance can race to intterupt 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);
> }
Signed-off-by: xiaoshoukui <xiaoshoukui@...jie.com.cn>
---
fs/btrfs/volumes.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 2ecb76cf3d91..886d667419ed 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -4638,8 +4638,7 @@ int btrfs_cancel_balance(struct btrfs_fs_info *fs_info)
}
}
- BUG_ON(fs_info->balance_ctl ||
- test_bit(BTRFS_FS_BALANCE_RUNNING, &fs_info->flags));
+ BUG_ON(test_bit(BTRFS_FS_BALANCE_RUNNING, &fs_info->flags));
atomic_dec(&fs_info->balance_cancel_req);
mutex_unlock(&fs_info->balance_mutex);
return 0;
--
2.34.1
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