linux-kernel - Re: [PATCH] erofs: Wake up all waiters after z_erofs_lzma

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Date:   Mon, 27 Jun 2022 13:57:54 +0800
From:   Yue Hu <zbestahu@...il.com>
To:     Yuwen Chen <chenyuwen1@...zu.com>
Cc:     <xiang@...nel.org>, linux-erofs@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] erofs: Wake up all waiters after z_erofs_lzma_head
 ready.

On Sat, 25 Jun 2022 22:50:00 +0800
Yuwen Chen <chenyuwen1@...zu.com> 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@...zu.com>
> ---
>  fs/erofs/decompressor_lzma.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/fs/erofs/decompressor_lzma.c b/fs/erofs/decompressor_lzma.c
> index 05a3063cf2bc..5e59b3f523eb 100644
> --- a/fs/erofs/decompressor_lzma.c
> +++ b/fs/erofs/decompressor_lzma.c
> @@ -143,6 +143,7 @@ int z_erofs_load_lzma_config(struct super_block *sb,
>  	DBG_BUGON(z_erofs_lzma_head);
>  	z_erofs_lzma_head = head;
>  	spin_unlock(&z_erofs_lzma_lock);
> +	wake_up_all(&z_erofs_lzma_wq);
>  
>  	z_erofs_lzma_max_dictsize = dict_size;
>  	mutex_unlock(&lzma_resize_mutex);

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