mirror of
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
synced 2026-04-03 12:05:13 +02:00
f8431b8672
[ Upstream commit 40534d19ed ]
The spidev driver previously used two mutexes, spi_lock and buf_lock,
but acquired them in different orders depending on the code path:
write()/read(): buf_lock -> spi_lock
ioctl(): spi_lock -> buf_lock
This AB-BA locking pattern triggers lockdep warnings and can
cause real deadlocks:
WARNING: possible circular locking dependency detected
spidev_ioctl() -> mutex_lock(&spidev->buf_lock)
spidev_sync_write() -> mutex_lock(&spidev->spi_lock)
*** DEADLOCK ***
The issue is reproducible with a simple userspace program that
performs write() and SPI_IOC_WR_MAX_SPEED_HZ ioctl() calls from
separate threads on the same spidev file descriptor.
Fix this by simplifying the locking model and removing the lock
inversion entirely. spidev_sync() no longer performs any locking,
and all callers serialize access using spi_lock.
buf_lock is removed since its functionality is fully covered by
spi_lock, eliminating the possibility of lock ordering issues.
This removes the lock inversion and prevents deadlocks without
changing userspace ABI or behaviour.
Signed-off-by: Fabian Godehardt <fg@emlix.com>
Link: https://patch.msgid.link/20260211072616.489522-1-fg@emlix.com
Signed-off-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>