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pinmux: fix race causing mux_owner NULL with active mux_usecount

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[ 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.qualcomm.com
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Mukesh Ojha
2025-07-08 13:28:38 +05:30
committed by Greg Kroah-Hartman
parent 33c778ea0b
commit 9b2a3e7189
1 changed files with 9 additions and 11 deletions
Download Patch File Download Diff File Expand all files Collapse all files

20
drivers/pinctrl/pinmux.c
View File

@@ -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;