jlaitine commented on code in PR #16194:
URL: https://github.com/apache/nuttx/pull/16194#discussion_r2059160520
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sched/semaphore/sem_wait.c:
##########
@@ -86,19 +89,62 @@ int nxsem_wait_slow(FAR sem_t *sem)
/* Check if the lock is available */
- if (atomic_fetch_sub(NXSEM_COUNT(sem), 1) > 0)
+ if (mutex)
+ {
+ uint32_t mholder;
+
+ /* We lock the mutex for us by setting the blocks bit,
+ * this is all that is needed if we block
+ */
+
+ mholder = atomic_fetch_or(NXSEM_MHOLDER(sem), NXSEM_MBLOCKS_BIT);
+ if (NXSEM_MACQUIRED(mholder))
+ {
+ /* htcb gets NULL if
+ * - the only holder did exit (without posting first)
+ * - the mutex was reset before
+ * In both cases we simply acquire the mutex, thus recovering
+ * from these situations.
+ */
+
+ htcb = nxsched_get_tcb(mholder & (~NXSEM_MBLOCKS_BIT));
+ }
+
+ unlocked = htcb == NULL;
+ }
+ else
+ {
+ unlocked = atomic_fetch_sub(NXSEM_COUNT(sem), 1) > 0;
+ }
+
+ if (unlocked)
{
/* It is, let the task take the semaphore. */
ret = nxsem_protect_wait(sem);
if (ret < 0)
{
- atomic_fetch_add(NXSEM_COUNT(sem), 1);
+ if (mutex)
+ {
+ atomic_set(NXSEM_MHOLDER(sem), NXSEM_NO_MHOLDER);
Review Comment:
Nope, I just corrected my reply above. This is the only holder of the mutex
now, but nxsem_protect_wait failed. So the correct value to restore this is to
NO_HOLDER. No-one can get in between.
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