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Date:   Mon, 27 Jun 2022 10:56:08 +0800
From:   Gao Xiang <hsiangkao@linux.alibaba.com>
To:     Yuwen Chen <chenyuwen1@meizu.com>
Cc:     xiang@kernel.org, chao@kernel.org, linux-erofs@lists.ozlabs.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] erofs: Wake up all waiters after z_erofs_lzma_head ready.
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References: <20220625145000.2720-1-chenyuwen1@meizu.com>
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On Sat, Jun 25, 2022 at 10:50:00PM +0800, Yuwen Chen wrote:
> When the user mounts the erofs second times, the decompression thread
> may hung. The problem happens due to a sequence of steps like the
> following:
> 
> 1) Task A called z_erofs_load_lzma_config which obtain all of the node
>    from the z_erofs_lzma_head.
> 
> 2) At this time, task B called the z_erofs_lzma_decompress and wanted to
>    get a node. But the z_erofs_lzma_head was empty, the Task B had to
>    sleep.
> 
> 3) Task A release nodes and push nodes into the z_erofs_lzma_head. But
>    task B was still sleeping.
> 
> One example report when the hung happens:
> task:kworker/u3:1 state:D stack:14384 pid: 86 ppid: 2 flags:0x00004000
> Workqueue: erofs_unzipd z_erofs_decompressqueue_work
> Call Trace:
>  <TASK>
>  __schedule+0x281/0x760
>  schedule+0x49/0xb0
>  z_erofs_lzma_decompress+0x4bc/0x580
>  ? cpu_core_flags+0x10/0x10
>  z_erofs_decompress_pcluster+0x49b/0xba0
>  ? __update_load_avg_se+0x2b0/0x330
>  ? __update_load_avg_se+0x2b0/0x330
>  ? update_load_avg+0x5f/0x690
>  ? update_load_avg+0x5f/0x690
>  ? set_next_entity+0xbd/0x110
>  ? _raw_spin_unlock+0xd/0x20
>  z_erofs_decompress_queue.isra.0+0x2e/0x50
>  z_erofs_decompressqueue_work+0x30/0x60
>  process_one_work+0x1d3/0x3a0
>  worker_thread+0x45/0x3a0
>  ? process_one_work+0x3a0/0x3a0
>  kthread+0xe2/0x110
>  ? kthread_complete_and_exit+0x20/0x20
>  ret_from_fork+0x22/0x30
>  </TASK>
> 
> Signed-off-by: Yuwen Chen <chenyuwen1@meizu.com>

Reviewed-by: Gao Xiang <hsiangkao@linux.alibaba.com>

Thanks,
Gao Xiang