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From: Hillf Danton <hdanton@sina.com>
To: Jaegeuk Kim <jaegeuk@kernel.org>
Cc: linux-kernel@vger.kernel.org,
	Light Hsieh =?utf-8?B?KOisneaYjueHiCk=?= <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 19:33:57 +0800
Message-Id: <20240322113357.2599-1-hdanton@sina.com>
In-Reply-To: <ZfzQz5hwECOEGYVL@google.com>
References: <20240320001442.497813-1-jaegeuk@kernel.org> <20240321224233.2541-1-hdanton@sina.com>
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On Thu, 21 Mar 2024 17:29:03 -0700 Jaegeuk Kim <jaegeuk@kernel.org>
> 
> I posted this patch before Light reported.

Yeah, his report's timestamp is 2024-03-20  6:59, nearly 7 hours later,
which shows that you constructed the deadlock with nothing to do with
his report.
> 
> And, in the report, I didn't get this:
> 
> f2fs_ioc_shutdown() --> freeze_bdev() --> freeze_super() --> sb_wait_write(sb, SB_FREEZE_FS) --> ... ->percpu_down_write().
> 
> because f2fs_ioc_shutdown() calls f2fs_stop_discard_thread() after thaw_bdev()
> like this order.
> 
>  -> freeze_bdev()
>  -> thaw_bdev()
>  -> f2fs_stop_discard_thread()
> 
> Am I missing something?

Light, could you specify to help Jaegeuk understand the deadlock you reported?