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Thu, 8 Jan 2026 08:19:09 -0500 (EST) Message-ID: <7cd19bb7-2aa8-4950-b0e0-c52d59f37f7d@bsbernd.com> Date: Thu, 8 Jan 2026 14:19:08 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [External] Re: [PATCH] fuse: add hang check in request_wait_answer() To: Joanne Koong , Zhang Tianci Cc: miklos@szeredi.hu, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, xieyongji@bytedance.com, zhujia.zj@bytedance.com, Jiachen Zhang References: <20251223062113.52477-1-zhangtianci.1997@bytedance.com> From: Bernd Schubert Content-Language: en-US, de-DE, fr In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Hi Joanne, On 1/8/26 01:00, Joanne Koong wrote: > On Tue, Jan 6, 2026 at 6:43 PM Zhang Tianci > wrote: >> >> Hi Joanne， >> >>> imo it's possible to check whether the kernel itself is affected just >>> purely through libfuse changes to fuse_lowlevel.c where the request >>> communication with the kernel happens. The number of requests ready by >>> the kernel is exposed to userspace through sysfs, so if the daemon is >>> deadlocked or cannot read fuse requests, that scenario is detectable >>> by userspace. > > Hi Tianci, > >> >> Yes, checking in libfuse/fuse_lowlevel.c is feasible, but it depends on >> the running state of FUSEDaemon(if FUSEDaemon is in a process exit state, >> this check cannot be performed), I think we do need this approach, >> but it cannot fully cover all scenarios. Therefore, I believe it >> should coexist with this patch. >> >> The content of the /sys/fs/fuse/connections/${devid}/waiting interface >> is inaccurate; >> it cannot distinguish between normal waiting and requests that have been hanging >> for a period of time. > > I think if the fusedaemon is in a process exit state (by "process exit > state", I think you're talking about the state where > fuse_session_exit() has been called but the daemon is stuck/hanging > before actual process exit?), this can still be detected in libfuse. > For example one idea could be libfuse spinning up a watchdog monitor > thread that has logic checking if the session's mt_exited has been set > with no progress on /sys/fs/fuse/.../waiting requests being fulfilled. I added one kernel connection watchdog last week https://github.com/libfuse/libfuse/commit/6278995cca991978abd25ebb2c20ebd3fc9e8a13 Thanks, Bernd