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{bp-19880} spinlock: fix ticket lock corruption in trylock and unlock #20072

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Merged
xiaoxiang781216 merged 1 commit into from
Sep 7, 2026
Merged

{bp-19880} spinlock: fix ticket lock corruption in trylock and unlock #20072

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18 changes: 12 additions & 6 deletions include/nuttx/spinlock.h
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Original file line number Diff line number Diff line change
Expand Up @@ -276,8 +276,18 @@ static inline_function bool
spin_trylock_notrace(FAR volatile spinlock_t *lock)
{
#ifdef CONFIG_TICKET_SPINLOCK
if (!atomic_cmpxchg(&lock->next, &lock->owner,
atomic_read(&lock->next) + 1))
/* The expected value must live in a local. A failed compare-exchange
* writes the current value of the target object back through the
* expected pointer, so passing &lock->owner here would clobber the
* owner counter and make a lock held by another CPU appear unlocked.
*
* The exchange succeeds only when next == owner, which is the unlocked
* state of a ticket lock.
*/

uint32_t expected = atomic_read(&lock->owner);

if (!atomic_cmpxchg(&lock->next, &expected, expected + 1))
#else /* CONFIG_TICKET_SPINLOCK */
if (up_testset(lock) == SP_LOCKED)
#endif /* CONFIG_TICKET_SPINLOCK */
Expand Down Expand Up @@ -394,7 +404,6 @@ spin_unlock_notrace(FAR volatile spinlock_t *lock)
****************************************************************************/

#ifdef CONFIG_SPINLOCK
# ifdef __SP_UNLOCK_FUNCTION
static inline_function void spin_unlock(FAR volatile spinlock_t *lock)
{
/* Unlock without trace note */
Expand All @@ -405,9 +414,6 @@ static inline_function void spin_unlock(FAR volatile spinlock_t *lock)

sched_note_spinlock_unlock(lock);
}
# else
# define spin_unlock(l) do { *(l) = SP_UNLOCKED; } while (0)
# endif
#else
# define spin_unlock(lock)
#endif /* CONFIG_SPINLOCK */
Expand Down
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