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[220.235.66.207]) by smtp.gmail.com with ESMTPSA id x190sm6948164pgb.79.2020.06.08.17.23.49 (version=TLS1_2 cipher=ECDHE-ECDSA-CHACHA20-POLY1305 bits=256/256); Mon, 08 Jun 2020 17:23:52 -0700 (PDT) Date: Tue, 9 Jun 2020 08:23:46 +0800 From: Kent Gibson To: Bartosz Golaszewski Cc: Linus Walleij , Andy Shevchenko , Greg Kroah-Hartman , linux-gpio@vger.kernel.org, linux-kernel@vger.kernel.org, Bartosz Golaszewski Subject: Re: [PATCH v4 12/13] gpiolib: add new ioctl() for monitoring changes in line info Message-ID: <20200609002346.GA6042@sol> References: <20191224120709.18247-1-brgl@bgdev.pl> <20191224120709.18247-13-brgl@bgdev.pl> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191224120709.18247-13-brgl@bgdev.pl> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-gpio-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-gpio@vger.kernel.org On Tue, Dec 24, 2019 at 01:07:08PM +0100, Bartosz Golaszewski wrote: > From: Bartosz Golaszewski > [snip!] > +static int lineinfo_changed_notify(struct notifier_block *nb, > + unsigned long action, void *data) > +{ > + struct gpio_chardev_data *priv = to_gpio_chardev_data(nb); > + struct gpioline_info_changed chg; > + struct gpio_desc *desc = data; > + int ret; > + > + if (!test_bit(desc_to_gpio(desc), priv->watched_lines)) > + return NOTIFY_DONE; > + > + memset(&chg, 0, sizeof(chg)); > + chg.info.line_offset = gpio_chip_hwgpio(desc); > + chg.event_type = action; > + chg.timestamp = ktime_get_real_ns(); > + gpio_desc_to_lineinfo(desc, &chg.info); > + Is this call legal? It can sleep - in fact you recently changed that very function to move a mutex call outside of a spinlock protected section. Here it is being called within an RCU lock, as lineinfo_changed_notify is at the end of an atomic_notifier_call_chain. I was looking at adding a chg.seqno here and considering what level of locking would be appropriate for the source counter when I noticed that call. Hopefully I'm missing something. Cheers, Kent.