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Mon, 24 Nov 2025 19:56:20 -0800 (PST) Message-ID: Date: Mon, 24 Nov 2025 20:56:18 -0700 Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: calling into file systems directly from ->queue_rq, was Re: [PATCH V5 0/6] loop: improve loop aio perf by IOCB_NOWAIT To: Ming Lei , Christoph Hellwig Cc: linux-block@vger.kernel.org, Mikulas Patocka , Zhaoyang Huang , Dave Chinner , linux-fsdevel@vger.kernel.org References: <20251015110735.1361261-1-ming.lei@redhat.com> Content-Language: en-US From: Jens Axboe In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 11/24/25 8:00 PM, Ming Lei wrote: > On Mon, Nov 24, 2025 at 01:05:46AM -0800, Christoph Hellwig wrote: >> On Mon, Nov 24, 2025 at 05:02:03PM +0800, Ming Lei wrote: >>> On Sun, Nov 23, 2025 at 10:12:24PM -0800, Christoph Hellwig wrote: >>>> FYI, with this series I'm seeing somewhat frequent stack overflows when >>>> using loop on top of XFS on top of stacked block devices. >>> >>> Can you share your setting? >>> >>> BTW, there are one followup fix: >>> >>> https://lore.kernel.org/linux-block/20251120160722.3623884-1-ming.lei@redhat.com/ >>> >>> I just run 'xfstests -q quick' on loop on top of XFS on top of dm-stripe, >>> not see stack overflow with the above fix against -next. >> >> This was with a development tree with lots of local code. So the >> messages aren't applicable (and probably a hint I need to reduce my >> stack usage). The observations is that we now stack through from block >> submission context into the file system write path, which is bad for a >> lot of reasons. journal_info being the most obvious one. >> >>>> In other words: I don't think issuing file system I/O from the >>>> submission thread in loop can work, and we should drop this again. >>> >>> I don't object to drop it one more time. >>> >>> However, can we confirm if it is really a stack overflow because of >>> calling into FS from ->queue_rq()? >> >> Yes. >> >>> If yes, it could be dead end to improve loop in this way, then I can give up. >> >> I think calling directly into the lower file system without a context >> switch is very problematic, so IMHO yes, it is a dead end. > > Hi Jens, > > Can you drop or revert the patchset of "loop: improve loop aio perf by IOCB_NOWAIT" > from for-6.19/block? Done -- Jens Axboe