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dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="g7V8xRvV" Received: by smtp.kernel.org (Postfix) with ESMTPSA id DBE22C433C7; Fri, 22 Mar 2024 00:29:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1711067345; bh=8QFd8esOMW5rZVdTF+FCShS/VOhr21smwFjuIbVf8dE=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=g7V8xRvVsvOYIV9nsn7wk/8oQODqnW3bKT4vXuj7EeiHsZ+kj++MuCorDx48ieYUf G7Y1xnz/pzb4pKo+fR0BafpSxjbyaaLlyNdci9vjsKIk14BFYR/PubUXqJb7615yJR 47rSc0li+j1pqD456aVwZl7cgQ7RRUetTkqwJXB2b2zOYEr2jC1oEumP71BempwFMr OVeeSHUxL5ABaKsD96mJWYbgfrY5q62x6ib3cK7AE+1MPV0gLb0g603UGhincMPicS 0Co3OaYkLDzXL/L138KGDrDKACJhYrZrVdHegpwZTneqPJ3pvPn545jjEG9hYN4pU8 jhCzcgD50JxYQ== Date: Thu, 21 Mar 2024 17:29:03 -0700 From: Jaegeuk Kim To: Hillf Danton Cc: linux-kernel@vger.kernel.org, Light Hsieh =?utf-8?B?KOisneaYjueHiCk=?= , linux-f2fs-devel@lists.sourceforge.net Subject: Re: [PATCH] f2fs: avoid the deadlock case when stopping discard thread Message-ID: References: <20240320001442.497813-1-jaegeuk@kernel.org> <20240321224233.2541-1-hdanton@sina.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20240321224233.2541-1-hdanton@sina.com> On 03/22, Hillf Danton wrote: > On Tue, 19 Mar 2024 17:14:42 -0700 Jaegeuk Kim > > 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? Damn. I couldn't think _write uses _read sem. > > > - 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. I posted this patch before Light reported. 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? > > Reported-by: "Light Hsieh (謝明燈)"