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[212.51.149.96]) by smtp.gmail.com with ESMTPSA id d2sm3745355eda.20.2019.10.15.07.07.27 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 15 Oct 2019 07:07:28 -0700 (PDT) Date: Tue, 15 Oct 2019 16:07:26 +0200 From: Daniel Vetter To: Johan Hovold Cc: Daniel Vetter , Rob Clark , Sean Paul , Fabien Dessenne , Mauro Carvalho Chehab , Harald Freudenberger , David Airlie , Heiko Carstens , Vasily Gorbik , Christian Borntraeger , linux-arm-msm@vger.kernel.org, dri-devel@lists.freedesktop.org, freedreno@lists.freedesktop.org, linux-kernel@vger.kernel.org, linux-media@vger.kernel.org, linux-s390@vger.kernel.org, Greg Kroah-Hartman , Al Viro Subject: Re: [PATCH 0/4] treewide: fix interrupted release Message-ID: <20191015140726.GN11828@phenom.ffwll.local> Mail-Followup-To: Johan Hovold , Rob Clark , Sean Paul , Fabien Dessenne , Mauro Carvalho Chehab , Harald Freudenberger , David Airlie , Heiko Carstens , Vasily Gorbik , Christian Borntraeger , linux-arm-msm@vger.kernel.org, dri-devel@lists.freedesktop.org, freedreno@lists.freedesktop.org, linux-kernel@vger.kernel.org, linux-media@vger.kernel.org, linux-s390@vger.kernel.org, Greg Kroah-Hartman , Al Viro References: <20191010131333.23635-1-johan@kernel.org> <20191010135043.GA16989@phenom.ffwll.local> <20191011093633.GD27819@localhost> <20191014084847.GD11828@phenom.ffwll.local> <20191014161326.GO13531@localhost> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191014161326.GO13531@localhost> X-Operating-System: Linux phenom 5.2.0-2-amd64 User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-arm-msm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-arm-msm@vger.kernel.org On Mon, Oct 14, 2019 at 06:13:26PM +0200, Johan Hovold wrote: > On Mon, Oct 14, 2019 at 10:48:47AM +0200, Daniel Vetter wrote: > > On Fri, Oct 11, 2019 at 11:36:33AM +0200, Johan Hovold wrote: > > > On Thu, Oct 10, 2019 at 03:50:43PM +0200, Daniel Vetter wrote: > > > > On Thu, Oct 10, 2019 at 03:13:29PM +0200, Johan Hovold wrote: > > > > > Two old USB drivers had a bug in them which could lead to memory leaks > > > > > if an interrupted process raced with a disconnect event. > > > > > > > > > > Turns out we had a few more driver in other subsystems with the same > > > > > kind of bug in them. > > > > > > > Random funny idea: Could we do some debug annotations (akin to > > > > might_sleep) that splats when you might_sleep_interruptible somewhere > > > > where interruptible sleeps are generally a bad idea? Like in > > > > fops->release? > > > > > > There's nothing wrong with interruptible sleep in fops->release per se, > > > it's just that drivers cannot return -ERESTARTSYS and friends and expect > > > to be called again later. > > > > Do you have a legit usecase for interruptible sleeps in fops->release? > > The tty layer depends on this for example when waiting for buffered > writes to complete (something which may never happen when using flow > control). > > > I'm not even sure killable is legit in there, since it's an fd, not a > > process context ... > > It will be run in process context in many cases, and for ttys we're good > AFAICT. Huh, read it a bit, all the ->shutdown callbacks have void return type. But there's indeed interruptible sleeps in there. Doesn't this break userspace that expects that a close() actually flushes the tty? Imo if you're ->release callbacks feels like it should do a wait to guaranteed something userspace expects, then doing a wait_interruptible/killable feels like a bug. Or alternatively, the wait isn't really needed in the first place. > > > The return value from release() is ignored by vfs, and adding a splat in > > > __fput() to catch these buggy drivers might be overkill. > > > > Ime once you have a handful of instances of a broken pattern, creating a > > check for it (under a debug option only ofc) is very much justified. > > Otherwise they just come back to life like the undead, all the time. And > > there's a _lot_ of fops->release callbacks in the kernel. > > Yeah, you have a point. > > But take tty again as an example, the close tty operation called from > release() is declared void so there's no propagated return value for vfs > to check. > > It may even be better to fix up the 100 or so callbacks potentially > returning non-zero and make fops->release void so that the compiler > would help us catch any future bugs and also serve as a hint for > developers that returning errnos from fops->release is probably not > what you want to do. > > But that's a lot of churn of course. Hm indeed ->release has int as return type. I guess that's needed for file I/O errno and similar stuff ... Still void return value doesn't catch funny stuff like doing interruptible waits and occasionally failing if you have a process that likes to use signals and also uses some library somewhere to do something. In graphics we have that, with Xorg loving signals for various things. -Daniel -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch From mboxrd@z Thu Jan 1 00:00:00 1970 From: Daniel Vetter Subject: Re: [PATCH 0/4] treewide: fix interrupted release Date: Tue, 15 Oct 2019 16:07:26 +0200 Message-ID: <20191015140726.GN11828@phenom.ffwll.local> References: <20191010131333.23635-1-johan@kernel.org> <20191010135043.GA16989@phenom.ffwll.local> <20191011093633.GD27819@localhost> <20191014084847.GD11828@phenom.ffwll.local> <20191014161326.GO13531@localhost> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: base64 Return-path: Content-Disposition: inline In-Reply-To: <20191014161326.GO13531@localhost> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: freedreno-bounces-PD4FTy7X32lNgt0PjOBp9y5qC8QIuHrW@public.gmane.org Sender: "Freedreno" To: Johan Hovold Cc: 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