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[194.223.74.160]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-8a9eef96e53sm791024b3a.20.2026.10.30.06.46.48 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 30 Oct 2026 06:46:52 -0700 (PDT) Date: Fri, 30 Oct 2026 21:46:39 +0800 From: Kent Gibson To: Adrian Ambrozewicz Cc: Bartosz Golaszewski , Linus Walleij , Bartosz Golaszewski , "Paul E. McKenney" , Herve Codina , Jia Jia , Andy Shevchenko , linux-gpio@vger.kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org, Sashiko Subject: Re: [PATCH v4 6/7] gpiolib: cdev: don't report a failed line read as an edge Message-ID: <20261030134639.GA94733@rigel> References: <20261029-gpiolib-chip-removal-v4-0-aambrozewicz@nvidia.com> <20261029-gpiolib-chip-removal-v4-6-aambrozewicz@nvidia.com> <20261030111435.GA76958@rigel> <20261030123109.1935475-2-aambrozewicz@nvidia.com> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261030123109.1935475-2-aambrozewicz@nvidia.com> On Fri, Oct 30, 2026 at 02:31:10PM +0200, Adrian Ambrozewicz wrote: > On Fri, Oct 30, 2026 at 07:14:35PM +0800, Kent Gibson wrote: > > > Fixes: 61f922db7221 ("gpio: userspace ABI for reading GPIO line events") > > > Fixes: 73e0341992b6 ("gpiolib: cdev: support edge detection for uAPI v2") > > > Fixes: 2068339a6c35 ("gpiolib: cdev: Add hardware timestamp clock type") > > > > How did you determine that? Those commits are where the associated blocks > > of code were first added - not where the problem first exhibited. > > From the hot-plug case in the message: a driver's ->get() error has > reached these checks since each was added. Removal is newer, as you > say. > > > The failure mode you are addressing was added by > > commit d83cee3d ("gpio: protect the pointer to gpio_chip in gpio_device with SRCU"). > > Prior to that gpiod_get_raw_value_commit(), and gpiod_get_value_cansleep() > > and gpiod_get_raw_value_cansleep() that wrap it, wouldn't return the error > > that you are handling. > > > > Could you bisect to confirm? > > Confirmed: with gpio-sim and delayed IRQ threads, a falling edge > during removal reads as falling on the parent of commit d83cee3d2bb1 > ("gpio: protect the pointer to gpio_chip in gpio_device with SRCU") > and as rising on it, 10 of 10 each. > > A test chip whose ->get() returns -EIO gives a rising edge on that > parent and on gpio/for-current, none with this patch. pcf857x and dln2 > already returned such errors at commit 61f922db7221 > ("gpio: userspace ABI for reading GPIO line events"). > Ok, so the driver ->get() itself may return an error if the physical chip has gone away. Hadn't considered that path. Could you update the commit message to better describe that case? > I would use Fixes: 61f922db7221 for ->get() errors and d83cee3d2bb1 > for removal. Is that OK? Not sure - I'll defer to Bart on that. Cheers, Kent.