libc/semaphore: Use the while loop to handle the inerrupt correctly

If atomic_try_cmpxchg_xxxx runs on LL/SC architectures (e.g.ARMv7,
ARMv8, RISC-V), the weak CAS expands to a single LDREX/STREX pair.

If the CPU takes an IRQ/FIQ/SVC between the two instructions,
hardware performs an implicit CLREX and the following STREX returns
1, therefore atomic_try_cmpxchg_xxxx return failure even though
*addr* still holds the expected value.

So let's retry atomic_try_cmpxchg_xxxx in this case.

Signed-off-by: Xiang Xiao <xiaoxiang@xiaomi.com>

libs/libc/semaphore/sem_post.c

@@ -151,24 +151,26 @@ int nxsem_post(FAR sem_t *sem)
     }
 #  endif
 
-  if (fastpath)
+  while (fastpath)
     {
-      int32_t old;
-      int32_t new;
       FAR atomic_t *val = mutex ? NXSEM_MHOLDER(sem) : NXSEM_COUNT(sem);
+      int32_t old = atomic_read(val);
+      int32_t new;
 
       if (mutex)
         {
-          old = _SCHED_GETTID();
+          if (NXSEM_MBLOCKING(old))
+            {
+              break;
+            }
+
           new = NXSEM_NO_MHOLDER;
         }
       else
         {
-          old = atomic_read(val);
-
           if (old < 0)
             {
-              goto out;
+              break;
             }
 
           new = old + 1;
@@ -179,9 +181,6 @@ int nxsem_post(FAR sem_t *sem)
           return OK;
         }
     }
-
-out:
-
 #else
   UNUSED(mutex);
   UNUSED(fastpath);

libs/libc/semaphore/sem_trywait.c

@@ -146,43 +146,35 @@ int nxsem_trywait(FAR sem_t *sem)
     }
 #  endif
 
-  if (fastpath)
+  while (fastpath)
     {
-      bool ret = false;
-      int32_t old;
-      int32_t new;
       FAR atomic_t *val = mutex ? NXSEM_MHOLDER(sem) : NXSEM_COUNT(sem);
+      int32_t old = atomic_read(val);
+      int32_t new;
 
       if (mutex)
         {
-          old = NXSEM_NO_MHOLDER;
+          if (old != NXSEM_NO_MHOLDER)
+            {
+              return -EAGAIN;
+            }
+
+          new = _SCHED_GETTID();
         }
       else
-        {
-          old = atomic_read(val);
-        }
-
-      do
-        {
-          if (!mutex)
         {
           if (old < 1)
             {
-                  break;
+              return -EAGAIN;
             }
 
           new = old - 1;
         }
-          else
+
+      if (atomic_try_cmpxchg_acquire(val, &old, new))
         {
-              new = _SCHED_GETTID();
+          return OK;
         }
-
-          ret = atomic_try_cmpxchg_acquire(NXSEM_MHOLDER(sem), &old, new);
-        }
-      while (!mutex && !ret);
-
-      return ret ? OK : -EAGAIN;
     }
 
 #else

libs/libc/semaphore/sem_wait.c

@@ -174,24 +174,26 @@ int nxsem_wait(FAR sem_t *sem)
     }
 #  endif
 
-  if (fastpath)
+  while (fastpath)
     {
-      int32_t old;
-      int32_t new;
       FAR atomic_t *val = mutex ? NXSEM_MHOLDER(sem) : NXSEM_COUNT(sem);
+      int32_t old = atomic_read(val);
+      int32_t new;
 
       if (mutex)
         {
-          old = NXSEM_NO_MHOLDER;
+          if (old != NXSEM_NO_MHOLDER)
+            {
+              break;
+            }
+
           new = _SCHED_GETTID();
         }
       else
         {
-          old = atomic_read(val);
-
           if (old < 1)
             {
-              goto out;
+              break;
             }
 
           new = old - 1;
@@ -202,9 +204,6 @@ int nxsem_wait(FAR sem_t *sem)
           return OK;
         }
     }
-
-out:
-
 #else
   UNUSED(mutex);
   UNUSED(fastpath);