linux-kernel - Re: f2fs F2FS_IOC

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Message-ID: <ZftBxmBFmGCFg35I@google.com>
Date: Wed, 20 Mar 2024 13:06:30 -0700
From: Jaegeuk Kim <jaegeuk@...nel.org>
To: Light Hsieh (謝明燈) <Light.Hsieh@...iatek.com>
Cc: Ed Tsai (蔡宗軒) <Ed.Tsai@...iatek.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-f2fs-devel@...ts.sourceforge.net" <linux-f2fs-devel@...ts.sourceforge.net>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	Chun-Hung Wu (巫駿宏) <Chun-hung.Wu@...iatek.com>
Subject: Re: f2fs F2FS_IOC_SHUTDOWN hang issue

Can you try this?

https://patchwork.kernel.org/project/f2fs/patch/20240320001442.497813-1-jaegeuk@kernel.org/

On 03/20, Light Hsieh (謝明燈) wrote:
> Hi Jaegeuk:
> 
> We encounter a deadlock issue when Android is going to poweroff.
> Please help check.
> 
> When unmounting of  f2fs partition fail in Android poweroff procedure, init thread (pid = 1) invoke F2FS_IOC_SHUTDOWN  ioctl with arg F2FS_GOING_DOWN_FULLSYNC.
> This ioctl cause down_write of a semaphore in the following call sequence:
>         f2fs_ioc_shutdown() --> freeze_bdev() --> freeze_super() --> sb_wait_write(sb, SB_FREEZE_FS) --> ... ->percpu_down_write().
> 
> f2fs_ioc_shutdown() will later invoke f2fs_stop_discard_thread() and wait for stopping of f2fs_discard thread in the following call sequence:
>         f2fs_ioc_shutdown() -->f2fs_stop_discard_thread() -->kthread_stop(discard_thread) --> wait_for_completion().
> That is, init thread go sleep with a write semaphore.
> 
> f2fs_discard thread is then waken up to process f2fs discard.
> However, f2fs_discard threshold may then hang because failing to get the semaphore aleady obtained by the slept init thread:
>         issue_discard_thread() --> sb_start_intwrite() -->sb_start_write(sb, SB_FREEZE_FS) --> percpu_down_read()
> 
> Light