[PATCH] erofs: Wake up all waiters after z_erofs_lzma_head ready.

[PATCH] erofs: Wake up all waiters after z_erofs_lzma_head ready.

[Even]

From: Even <chenyuwen1@meizu.com>

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: Even <chenyuwen1@meizu.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);
-- 
2.25.1

Re: [PATCH] erofs: Wake up all waiters after z_erofs_lzma_head ready.

[Gao Xiang]

Hi,

On Sat, Jun 25, 2022 at 04:57:38PM +0800, Even wrote:
> From: Even <chenyuwen1@meizu.com>
> 
> 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: Even <chenyuwen1@meizu.com>

Thanks a lot for catching this!

The patch itself looks good, but could you use your real name to sign
off the patch and resend a version? see,
https://www.kernel.org/doc/html/v4.17/process/submitting-patches.html#developer-s-certificate-of-origin-1-1

Otherwise it looks good to me,
Reviewed-by: Gao Xiang <hsiangkao@linux.alibaba.com>

Thanks,
Gao Xiang

Re:Re: [PATCH] erofs: Wake up all waiters after z_erofs_lzma_head ready.

[cheny_wen]

Hi
     I have sent a new email from meizu email which signed the patch.

thinks for your help.
在 2022-06-25 17:44:48，"Gao Xiang" <hsiangkao@linux.alibaba.com> 写道：
Hi,

On Sat, Jun 25, 2022 at 04:57:38PM +0800, Even wrote:
> From: Even <chenyuwen1@meizu.com>
> 
> 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: Even <chenyuwen1@meizu.com>

Thanks a lot for catching this!

The patch itself looks good, but could you use your real name to sign
off the patch and resend a version? see,
https://www.kernel.org/doc/html/v4.17/process/submitting-patches.html#developer-s-certificate-of-origin-1-1

Otherwise it looks good to me,
Reviewed-by: Gao Xiang <hsiangkao@linux.alibaba.com>

Thanks,
Gao Xiang