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From:   Chengfeng Ye <dg573847474@gmail.com>
To:     linus.walleij@linaro.org, brgl@bgdev.pl, andy@kernel.org
Cc:     linux-gpio@vger.kernel.org, linux-kernel@vger.kernel.org,
        cyeaa@connect.ust.hk, Chengfeng Ye <dg573847474@gmail.com>
Subject: [PATCH v2 1/2] gpiolib: cdev: Fix &lr->wait.lock deadlock issue
Date:   Mon, 26 Jun 2023 14:57:55 +0000
Message-Id: <20230626145756.30696-1-dg573847474@gmail.com>
Precedence: bulk

linereq_put_event() is called from both interrupt context (e.g.,
edge_irq_thread()) and process context (process_hw_ts_thread()).
Therefore, interrupt should be disabled before acquiring lock
&lr->wait.lock inside linereq_put_event() to avoid deadlock when
the lock is held in process context and edge_irq_thread() comes.

Similarly, linereq_read_unlocked() running in process context
also acquies the same lock. It also need to disable interrupt
otherwise deadlock could happen if the irq edge_irq_thread()
comes to execution while the lock is held.

Fix the two potential deadlock issues by spin_lock_bh() and
spin_lock_irq() separately.

Fixes: 73e0341992b6 ("gpiolib: cdev: support edge detection for uAPI v2")
Signed-off-by: Chengfeng Ye <dg573847474@gmail.com>
---
 drivers/gpio/gpiolib-cdev.c | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/drivers/gpio/gpiolib-cdev.c b/drivers/gpio/gpiolib-cdev.c
index 0a33971c964c..f768d46bdea7 100644
--- a/drivers/gpio/gpiolib-cdev.c
+++ b/drivers/gpio/gpiolib-cdev.c
@@ -615,13 +615,13 @@ static void linereq_put_event(struct linereq *lr,
 {
 	bool overflow = false;
 
-	spin_lock(&lr->wait.lock);
+	spin_lock_bh(&lr->wait.lock);
 	if (kfifo_is_full(&lr->events)) {
 		overflow = true;
 		kfifo_skip(&lr->events);
 	}
 	kfifo_in(&lr->events, le, 1);
-	spin_unlock(&lr->wait.lock);
+	spin_unlock_bh(&lr->wait.lock);
 	if (!overflow)
 		wake_up_poll(&lr->wait, EPOLLIN);
 	else
@@ -1514,28 +1514,28 @@ static ssize_t linereq_read_unlocked(struct file *file, char __user *buf,
 		return -EINVAL;
 
 	do {
-		spin_lock(&lr->wait.lock);
+		spin_lock_irq(&lr->wait.lock);
 		if (kfifo_is_empty(&lr->events)) {
 			if (bytes_read) {
-				spin_unlock(&lr->wait.lock);
+				spin_unlock_irq(&lr->wait.lock);
 				return bytes_read;
 			}
 
 			if (file->f_flags & O_NONBLOCK) {
-				spin_unlock(&lr->wait.lock);
+				spin_unlock_irq(&lr->wait.lock);
 				return -EAGAIN;
 			}
 
-			ret = wait_event_interruptible_locked(lr->wait,
+			ret = wait_event_interruptible_locked_irq(lr->wait,
 					!kfifo_is_empty(&lr->events));
 			if (ret) {
-				spin_unlock(&lr->wait.lock);
+				spin_unlock_irq(&lr->wait.lock);
 				return ret;
 			}
 		}
 
 		ret = kfifo_out(&lr->events, &le, 1);
-		spin_unlock(&lr->wait.lock);
+		spin_unlock_irq(&lr->wait.lock);
 		if (ret != 1) {
 			/*
 			 * This should never happen - we were holding the
-- 
2.17.1