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From: Hillf Danton <hdanton@sina.com>
To: Jaegeuk Kim <jaegeuk@kernel.org>
Cc: linux-kernel@vger.kernel.org,
	=?UTF-8?q?Light=20Hsieh=20=28=E8=AC=9D=E6=98=8E=E7=87=88=29?= <Light.Hsieh@mediatek.com>,
	linux-f2fs-devel@lists.sourceforge.net
Subject: Re: [PATCH] f2fs: avoid the deadlock case when stopping discard thread
Date: Fri, 22 Mar 2024 06:42:33 +0800
Message-Id: <20240321224233.2541-1-hdanton@sina.com>
In-Reply-To: <20240320001442.497813-1-jaegeuk@kernel.org>
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On Tue, 19 Mar 2024 17:14:42 -0700 Jaegeuk Kim <jaegeuk@kernel.org>
> f2fs_ioc_shutdown(F2FS_GOING_DOWN_NOSYNC)  issue_discard_thread
>  - mnt_want_write_file()
>    - sb_start_write(SB_FREEZE_WRITE)
	 __sb_start_write()
	   percpu_down_read()
>                                              - sb_start_intwrite(SB_FREEZE_FS);
						   __sb_start_write()
						     percpu_down_read()

Given lock acquirers for read on both sides, wtf deadlock are you fixing?

>  - f2fs_stop_checkpoint(sbi, false,            : waiting
>     STOP_CP_REASON_SHUTDOWN);
>  - f2fs_stop_discard_thread(sbi);
>    - kthread_stop()
>      : waiting
> 
>  - mnt_drop_write_file(filp);

More important, feel free to add in spin.

	Reported-by: "Light Hsieh (謝明燈)" <Light.Hsieh@mediatek.com>