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Tue, 15 Oct 2024 03:56:35 -0700 (PDT) From: Bartosz Golaszewski Date: Tue, 15 Oct 2024 12:56:16 +0200 Subject: [PATCH v3 4/6] gpio: cdev: put emitting the line state events on a workqueue Precedence: bulk X-Mailing-List: linux-gpio@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Message-Id: <20241015-gpio-notify-in-kernel-events-v3-4-9edf05802271@linaro.org> References: <20241015-gpio-notify-in-kernel-events-v3-0-9edf05802271@linaro.org> In-Reply-To: <20241015-gpio-notify-in-kernel-events-v3-0-9edf05802271@linaro.org> To: Linus Walleij , Bartosz Golaszewski , Kent Gibson Cc: linux-gpio@vger.kernel.org, linux-kernel@vger.kernel.org, Bartosz Golaszewski X-Mailer: b4 0.13.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=4901; i=bartosz.golaszewski@linaro.org; h=from:subject:message-id; bh=f8lvTlR7jwkkQHTiOBQ0YBYlycUUnx2/1dVqc+JGfAw=; b=owEBbQKS/ZANAwAKARGnLqAUcddyAcsmYgBnDkpe39urhIK2g2iZKIfiIdJYk0gGf71GbpYBz E/dfDumy3eJAjMEAAEKAB0WIQQWnetsC8PEYBPSx58Rpy6gFHHXcgUCZw5KXgAKCRARpy6gFHHX coaLEACZ+jXIKIcTgPJRx+YuzqYx+JNnJ1HTOu6bF/kUDBLmTOpkfmelTrIrY1gW5myTxvGtMdL 0zHa/PaRyWZD/RHQA0+iwuJrwBGssbG324Y2fdguJmxyaTHwT39yojGSNGw0FgHGU8a21xIG22u YzXhfMSSgr+e/wm+Jfv5rL1SUPcYpSWc64n+1nOwgJnnGfuvudYuKlVvf3bjdUkjLVB41DscKnt tQ9Rctdg7PPvsJKTYpMnEFkDl2dX+Q9RnK0HSa8vPFmvnsA42iGz5Rn2LWe46lG0PsIxFSTkXnd Su8CcPARCmITnLUh+qeZ7SLxgE7GAGUNkAmHy3XhmMKErfQ+tVr4W5CxmNU6KG6g1REaPTd4q+P NUsN1KvmQ/0gDoWDxxwZmnjGLHj3A/gI97j6TQF2E82fxh/yuApgL9SY3RW7QNDa2ABGhqF98oZ OR8JUcVOK1Y1I1U99wyUEujKGUOGMFZJWMnafYGUofcStMt6qy6itPh59mtNhhMb0imKlAa8/C3 Ls0oom4SoUtP4qsGL3ZUprZad/vFV6PUMXbaOWg949HWhLHgG+fMLxaWwLZIENTPFeOGrExGoCI k8I2hKBUu5KYY4u3QkSAZ62+I7URLv+PMBuWWUL7UJ/aHySM3+tcg2RRq4xtDQBjed6DOI4rF6Y H2fEX/OBPVvz1qg== X-Developer-Key: i=bartosz.golaszewski@linaro.org; a=openpgp; fpr=169DEB6C0BC3C46013D2C79F11A72EA01471D772 From: Bartosz Golaszewski In order to allow line state notifications to be emitted from atomic context (for instance: from gpiod_direction_input/output()), we must stop calling any sleeping functions in lineinfo_changed_notify(). To that end let's use the new workqueue. Let's atomically allocate small structures containing the required data and fill it with information immediately upon being notified about the change except for the pinctrl state which will be retrieved later from process context. We can pretty reliably do this as pin functions are typically set once per boot. Let's make sure to bump the reference count of GPIO device and the GPIO character device file descriptor to keep both alive until the event was queued. Signed-off-by: Bartosz Golaszewski --- drivers/gpio/gpiolib-cdev.c | 84 ++++++++++++++++++++++++++++++++++++++------- 1 file changed, 72 insertions(+), 12 deletions(-) diff --git a/drivers/gpio/gpiolib-cdev.c b/drivers/gpio/gpiolib-cdev.c index 5b28a558c9d0..a10d6ea22415 100644 --- a/drivers/gpio/gpiolib-cdev.c +++ b/drivers/gpio/gpiolib-cdev.c @@ -2450,6 +2450,7 @@ struct gpio_chardev_data { #ifdef CONFIG_GPIO_CDEV_V1 atomic_t watch_abi_version; #endif + struct file *fp; }; static int chipinfo_get(struct gpio_chardev_data *cdev, void __user *ip) @@ -2620,29 +2621,87 @@ static long gpio_ioctl_compat(struct file *file, unsigned int cmd, } #endif +struct lineinfo_changed_ctx { + struct work_struct work; + struct gpio_v2_line_info_changed chg; + struct gpio_device *gdev; + struct gpio_chardev_data *cdev; +}; + +static void lineinfo_changed_func(struct work_struct *work) +{ + struct lineinfo_changed_ctx *ctx = + container_of(work, struct lineinfo_changed_ctx, work); + struct gpio_chip *gc; + int ret; + + if (!(ctx->chg.info.flags & GPIO_V2_LINE_FLAG_USED)) { + /* + * If nobody set the USED flag earlier, let's see with pinctrl + * now. We're doing this late because it's a sleeping function. + * Pin functions are in general much more static and while it's + * not 100% bullet-proof, it's good enough for most cases. + */ + scoped_guard(srcu, &ctx->gdev->srcu) { + gc = srcu_dereference(ctx->gdev->chip, &ctx->gdev->srcu); + if (gc && + !pinctrl_gpio_can_use_line(gc, ctx->chg.info.offset)) + ctx->chg.info.flags |= GPIO_V2_LINE_FLAG_USED; + } + } + + ret = kfifo_in_spinlocked(&ctx->cdev->events, &ctx->chg, 1, + &ctx->cdev->wait.lock); + if (ret) + wake_up_poll(&ctx->cdev->wait, EPOLLIN); + else + pr_debug_ratelimited("lineinfo event FIFO is full - event dropped\n"); + + gpio_device_put(ctx->gdev); + fput(ctx->cdev->fp); + kfree(ctx); +} + static int lineinfo_changed_notify(struct notifier_block *nb, unsigned long action, void *data) { struct gpio_chardev_data *cdev = container_of(nb, struct gpio_chardev_data, lineinfo_changed_nb); - struct gpio_v2_line_info_changed chg; + struct lineinfo_changed_ctx *ctx; struct gpio_desc *desc = data; - int ret; if (!test_bit(gpio_chip_hwgpio(desc), cdev->watched_lines)) return NOTIFY_DONE; - memset(&chg, 0, sizeof(chg)); - chg.event_type = action; - chg.timestamp_ns = ktime_get_ns(); - gpio_desc_to_lineinfo(desc, &chg.info, false); - supinfo_to_lineinfo(desc, &chg.info); + /* + * If this is called from atomic context (for instance: with a spinlock + * taken by the atomic notifier chain), any sleeping calls must be done + * outside of this function in process context of the dedicated + * workqueue. + * + * Let's gather as much info as possible from the descriptor and + * postpone just the call to pinctrl_gpio_can_use_line() until the work + * is executed. + */ - ret = kfifo_in_spinlocked(&cdev->events, &chg, 1, &cdev->wait.lock); - if (ret) - wake_up_poll(&cdev->wait, EPOLLIN); - else - pr_debug_ratelimited("lineinfo event FIFO is full - event dropped\n"); + ctx = kzalloc(sizeof(*ctx), GFP_ATOMIC); + if (!ctx) { + pr_err("Failed to allocate memory for line info notification\n"); + return NOTIFY_DONE; + } + + ctx->chg.event_type = action; + ctx->chg.timestamp_ns = ktime_get_ns(); + gpio_desc_to_lineinfo(desc, &ctx->chg.info, true); + supinfo_to_lineinfo(desc, &ctx->chg.info); + /* Keep the GPIO device alive until we emit the event. */ + ctx->gdev = gpio_device_get(desc->gdev); + ctx->cdev = cdev; + /* Keep the file descriptor alive too. */ + get_file(ctx->cdev->fp); + + INIT_WORK(&ctx->work, lineinfo_changed_func); + queue_work(ctx->gdev->line_state_wq, &ctx->work); return NOTIFY_OK; } @@ -2802,6 +2861,7 @@ static int gpio_chrdev_open(struct inode *inode, struct file *file) goto out_unregister_line_notifier; file->private_data = cdev; + cdev->fp = file; ret = nonseekable_open(inode, file); if (ret)