6.15-stable review patch. If anyone has any objections, please let me know.
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From: Mukesh Ojha mukesh.ojha@oss.qualcomm.com
[ Upstream commit 0b075c011032f88d1cfde3b45d6dcf08b44140eb ]
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.
Fixes: 5a3e85c3c397 ("pinmux: Use sequential access to access desc->pinmux data") Signed-off-by: Mukesh Ojha mukesh.ojha@oss.qualcomm.com Link: https://lore.kernel.org/20250708-pinmux-race-fix-v2-1-8ae9e8a0d1a1@oss.qualc... Signed-off-by: Linus Walleij linus.walleij@linaro.org Signed-off-by: Sasha Levin sashal@kernel.org --- 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 0743190da59e..2c31e7f2a27a 100644 --- a/drivers/pinctrl/pinmux.c +++ b/drivers/pinctrl/pinmux.c @@ -236,18 +236,7 @@ static const char *pin_free(struct pinctrl_dev *pctldev, int pin, if (desc->mux_usecount) return NULL; } - } - - /* - * If there is no kind of request function for the pin we just assume - * we got it by default and proceed. - */ - if (gpio_range && ops->gpio_disable_free) - ops->gpio_disable_free(pctldev, gpio_range, 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; @@ -258,6 +247,15 @@ static const char *pin_free(struct pinctrl_dev *pctldev, int pin, } }
+ /* + * If there is no kind of request function for the pin we just assume + * we got it by default and proceed. + */ + if (gpio_range && ops->gpio_disable_free) + ops->gpio_disable_free(pctldev, gpio_range, pin); + else if (ops->free) + ops->free(pctldev, pin); + module_put(pctldev->owner);
return owner;