From 2dabc476cf95d9303aee3f6766878584ea3a246b Mon Sep 17 00:00:00 2001 From: Mukesh Ojha Date: Tue, 8 Jul 2025 13:28:38 +0530 Subject: [PATCH] FROMGIT: pinmux: fix race causing mux_owner NULL with active mux_usecount commit 5a3e85c3c397 ("pinmux: Use sequential access to access desc->pinmux data") tried to address the issue when two client of the same gpio calls pinctrl_select_state() for the same functionality, was resulting in NULL pointer issue while accessing desc->mux_owner. However, issue was not completely fixed due to the way it was handled and it can still result in the same NULL pointer. The issue occurs due to the following interleaving: cpu0 (process A) cpu1 (process B) pin_request() { pin_free() { mutex_lock() desc->mux_usecount--; //becomes 0 .. mutex_unlock() mutex_lock(desc->mux) desc->mux_usecount++; // becomes 1 desc->mux_owner = owner; mutex_unlock(desc->mux) mutex_lock(desc->mux) desc->mux_owner = NULL; mutex_unlock(desc->mux) This sequence leads to a state where the pin appears to be in use (`mux_usecount == 1`) but has no owner (`mux_owner == NULL`), which can cause NULL pointer on next pin_request on the same pin. Ensure that updates to mux_usecount and mux_owner are performed atomically under the same lock. Only clear mux_owner when mux_usecount reaches zero and no new owner has been assigned. Bug: 430525600 Fixes: 5a3e85c3c397 ("pinmux: Use sequential access to access desc->pinmux data") Link: https://lore.kernel.org/lkml/20250708-pinmux-race-fix-v2-1-8ae9e8a0d1a1@oss.qualcomm.com/ Signed-off-by: Mukesh Ojha (cherry picked from commit 0b075c011032f88d1cfde3b45d6dcf08b44140eb git://git.kernel.org/pub/scm/linux/kernel/git/linusw/linux-pinctrl.git for-next) Change-Id: Iec29ea201ef0fc3d205bbc4f1a90cb5a56a62039 Signed-off-by: Mukesh Ojha --- drivers/pinctrl/pinmux.c | 20 +++++++++----------- 1 file changed, 9 insertions(+), 11 deletions(-) diff --git a/drivers/pinctrl/pinmux.c b/drivers/pinctrl/pinmux.c index 97e8af88df85..ab853d6c586b 100644 --- a/drivers/pinctrl/pinmux.c +++ b/drivers/pinctrl/pinmux.c @@ -238,6 +238,15 @@ static const char *pin_free(struct pinctrl_dev *pctldev, int pin, if (desc->mux_usecount) return NULL; } + + if (gpio_range) { + owner = desc->gpio_owner; + desc->gpio_owner = NULL; + } else { + owner = desc->mux_owner; + desc->mux_owner = NULL; + desc->mux_setting = NULL; + } } /* @@ -249,17 +258,6 @@ static const char *pin_free(struct pinctrl_dev *pctldev, int pin, else if (ops->free) ops->free(pctldev, pin); - scoped_guard(mutex, &desc->mux_lock) { - if (gpio_range) { - owner = desc->gpio_owner; - desc->gpio_owner = NULL; - } else { - owner = desc->mux_owner; - desc->mux_owner = NULL; - desc->mux_setting = NULL; - } - } - module_put(pctldev->owner); return owner;