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Tue, 02 Jun 2026 21:02:49 -0700 (PDT) From: Rosen Penev To: linux-watchdog@vger.kernel.org Cc: Wim Van Sebroeck , Guenter Roeck , linux-kernel@vger.kernel.org (open list) Subject: [PATCH v2 1/2] watchdog: pika_wdt: fix timer leak and close race Date: Tue, 2 Jun 2026 21:02:29 -0700 Message-ID: <20260603040230.318998-2-rosenp@gmail.com> X-Mailer: git-send-email 2.54.0 In-Reply-To: <20260603040230.318998-1-rosenp@gmail.com> References: <20260603040230.318998-1-rosenp@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Two timer lifecycle bugs in the PIKA watchdog driver: 1. pikawdt_exit() unmaps the FPGA IO memory without stopping the ping timer. A timer tick after iounmap executes pikawdt_ping() on freed memory. Add timer_delete_sync() before iounmap. 2. pikawdt_release() uses timer_delete() which does not synchronize with a concurrently executing timer handler. If pikawdt_ping() runs on another CPU after timer_delete() marks the timer as deleted but before the open bit is cleared, it can call mod_timer() and re-arm itself. Once the open bit is subsequently cleared, the condition (!nowayout && !open) becomes true and the timer keeps patting the watchdog forever, defeating the intended reset-on-unexpected-close. Fix by clearing the open bit before calling timer_delete_sync(), which waits for any in-flight handler to complete. Assisted-by: opencode:big-pickle Signed-off-by: Rosen Penev --- drivers/watchdog/pika_wdt.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/drivers/watchdog/pika_wdt.c b/drivers/watchdog/pika_wdt.c index 87b8988d2520..60a846cb3601 100644 --- a/drivers/watchdog/pika_wdt.c +++ b/drivers/watchdog/pika_wdt.c @@ -127,11 +127,12 @@ static int pikawdt_open(struct inode *inode, struct file *file) */ static int pikawdt_release(struct inode *inode, struct file *file) { + clear_bit(0, &pikawdt_private.open); + /* stop internal ping */ if (!pikawdt_private.expect_close) - timer_delete(&pikawdt_private.timer); + timer_delete_sync(&pikawdt_private.timer); - clear_bit(0, &pikawdt_private.open); pikawdt_private.expect_close = 0; return 0; } @@ -291,6 +292,7 @@ static void __exit pikawdt_exit(void) { misc_deregister(&pikawdt_miscdev); + timer_delete_sync(&pikawdt_private.timer); iounmap(pikawdt_private.fpga); } -- 2.54.0