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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>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
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In order to build the documentation, use ``make htmldocs`` or
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https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.