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From:   Yi Li <yilikernel@gmail.com>
Date:   Tue, 1 Dec 2020 12:35:06 +0800
Message-ID: <CAJfdMYDnDJXFVfEECtQ9-E4F9kfsF035PH+x3kaVn6PPSYCydA@mail.gmail.com>
Subject: Re: [PATCH] bcache: fix panic due to cache_set is null
To:     Yi Li <yili@winhong.com>
Cc:     colyli@suse.de, kent.overstreet@gmail.com,
        linux-bcache@vger.kernel.org, linux-kernel@vger.kernel.org,
        Guo Chao <guochao@winhong.com>
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sorry, This patch will cause deadlock, i will check and redo it.

On 11/30/20, Yi Li <yili@winhong.com> wrote:
> bcache_device_detach will release the cache_set after hotunplug cache
> disk. update_writeback_rate should check validate of cache_set.
>
>   IP: [<ffffffffa03730c9>] update_writeback_rate+0x59/0x3a0 [bcache]
>   PGD 879620067 PUD 8755d3067 PMD 0
>   Oops: 0000 [#1] SMP
>   CPU: 8 PID: 1005702 Comm: kworker/8:0 Tainted: G 4.4.0+10 #1
>   Hardware name: Intel BIOS SE5C610.86B.01.01.0021.032120170601 03/21/2017
>   Workqueue: events update_writeback_rate [bcache]
>   task: ffff8808786f3800 ti: ffff88077082c000 task.ti: ffff88077082c000
>   RIP: e030:[<ffffffffa03730c9>] update_writeback_rate+0x59/0x3a0 [bcache]
>   RSP: e02b:ffff88077082fde0  EFLAGS: 00010202
>   RAX: 0000000000000018 RBX: ffff8808047f0b08 RCX: 0000000000000000
>   RDX: 0000000000000001 RSI: ffff88088170dab8 RDI: ffff88088170dab8
>   RBP: ffff88077082fe18 R08: 000000000000000a R09: 0000000000000000
>   R10: 0000000000000000 R11: 0000000000017bc8 R12: 0000000000000000
>   R13: ffff8808047f0000 R14: 0000000000000200 R15: ffff8808047f0b08
>   FS:  00007f157b6d6700(0000) GS:ffff880881700000(0000)
> knlGS:0000000000000000
>   CS:  e033 DS: 0000 ES: 0000 CR0: 0000000080050033
>   CR2: 0000000000000368 CR3: 0000000875c05000 CR4: 0000000000040660
>   Stack:
>    0000000000000001 0000000000007ff0 ffff88085ff600c0 ffff880881714e80
>    ffff880881719500 0000000000000200 ffff8808047f0b08 ffff88077082fe60
>    ffffffff81088c0c 0000000081714e80 0000000000000000 ffff880881714e80
>   Call Trace:
>    [<ffffffff81088c0c>] process_one_work+0x1fc/0x3b0
>    [<ffffffff81089575>] worker_thread+0x2a5/0x470
>    [<ffffffff815a2f58>] ? __schedule+0x648/0x870
>    [<ffffffff810892d0>] ? rescuer_thread+0x300/0x300
>    [<ffffffff8108e3d5>] kthread+0xd5/0xe0
>    [<ffffffff8108e300>] ? kthread_stop+0x110/0x110
>    [<ffffffff815a704f>] ret_from_fork+0x3f/0x70
>    [<ffffffff8108e300>] ? kthread_stop+0x110/0x110
>
> Reported-by: Guo Chao <guochao@winhong.com>
> Signed-off-by: Guo Chao <guochao@winhong.com>
> Signed-off-by: Yi Li <yili@winhong.com>
> ---
>  drivers/md/bcache/writeback.c | 12 +++++++++++-
>  1 file changed, 11 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/md/bcache/writeback.c b/drivers/md/bcache/writeback.c
> index 3c74996978da..186c4c6e1607 100644
> --- a/drivers/md/bcache/writeback.c
> +++ b/drivers/md/bcache/writeback.c
> @@ -175,7 +175,15 @@ static void update_writeback_rate(struct work_struct
> *work)
>  	struct cached_dev *dc = container_of(to_delayed_work(work),
>  					     struct cached_dev,
>  					     writeback_rate_update);
> -	struct cache_set *c = dc->disk.c;
> +	struct cache_set *c = NULL;
> +
> +	mutex_lock(&bch_register_lock);
> +	c = dc->disk.c;
> +
> +	if (c == NULL) {
> +		mutex_unlock(&bch_register_lock);
> +		return;
> +	}
>
>  	/*
>  	 * should check BCACHE_DEV_RATE_DW_RUNNING before calling
> @@ -194,6 +202,7 @@ static void update_writeback_rate(struct work_struct
> *work)
>  		clear_bit(BCACHE_DEV_RATE_DW_RUNNING, &dc->disk.flags);
>  		/* paired with where BCACHE_DEV_RATE_DW_RUNNING is tested */
>  		smp_mb__after_atomic();
> +		mutex_unlock(&bch_register_lock);
>  		return;
>  	}
>
> @@ -230,6 +239,7 @@ static void update_writeback_rate(struct work_struct
> *work)
>  	clear_bit(BCACHE_DEV_RATE_DW_RUNNING, &dc->disk.flags);
>  	/* paired with where BCACHE_DEV_RATE_DW_RUNNING is tested */
>  	smp_mb__after_atomic();
> +	mutex_unlock(&bch_register_lock);
>  }
>
>  static unsigned int writeback_delay(struct cached_dev *dc,
> --
> 2.25.3
>
>
>
>