Version 0.8.11

[userspace-rcu.git] / urcu.c

diff --git a/urcu.c b/urcu.c
index a26d38fbaca8286ffe1f6fe3bd522e5a2740a34f..bf2a66bfe3ec360613497d6a7b7c0da2cddc10e9 100644 (file)
--- a/urcu.c
+++ b/urcu.c
@@ -64,18 +64,10 @@
 #define RCU_QS_ACTIVE_ATTEMPTS 100
 
 /*
- * RCU_MEMBARRIER is only possibly available on Linux.
+ * The ABI of sys_membarrier changed after its original implementation.
+ * Disable it for now. Use RCU_MB flavor instead.
  */
-#if defined(RCU_MEMBARRIER) && defined(__linux__)
-#include <syscall.h>
-#endif
-
-/* If the headers do not support SYS_membarrier, fall back on RCU_MB */
-#ifdef SYS_membarrier
-# define membarrier(...)               syscall(SYS_membarrier, __VA_ARGS__)
-#else
-# define membarrier(...)               -ENOSYS
-#endif
+#define membarrier(...)                -ENOSYS
 
 #define MEMBARRIER_EXPEDITED           (1 << 0)
 #define MEMBARRIER_DELAYED             (1 << 1)
@@ -231,19 +223,27 @@ static void smp_mb_master(int group)
 
 /*
  * synchronize_rcu() waiting. Single thread.
+ * Always called with rcu_registry lock held. Releases this lock and
+ * grabs it again. Holds the lock when it returns.
  */
 static void wait_gp(void)
 {
-       /* Read reader_gp before read futex */
+       /*
+        * Read reader_gp before read futex. smp_mb_master() needs to
+        * be called with the rcu registry lock held in RCU_SIGNAL
+        * flavor.
+        */
        smp_mb_master(RCU_MB_GROUP);
+       /* Temporarily unlock the registry lock. */
+       mutex_unlock(&rcu_registry_lock);
        if (uatomic_read(&rcu_gp.futex) != -1)
-               return;
+               goto end;
        while (futex_async(&rcu_gp.futex, FUTEX_WAIT, -1,
                        NULL, NULL, 0)) {
                switch (errno) {
                case EWOULDBLOCK:
                        /* Value already changed. */
-                       return;
+                       goto end;
                case EINTR:
                        /* Retry if interrupted by signal. */
                        break;  /* Get out of switch. */
@@ -252,6 +252,11 @@ static void wait_gp(void)
                        urcu_die(errno);
                }
        }
+end:
+       /*
+        * Re-lock the registry lock before the next loop.
+        */
+       mutex_lock(&rcu_registry_lock);
 }
 
 /*
@@ -314,14 +319,19 @@ static void wait_for_readers(struct cds_list_head *input_readers,
                        }
                        break;
                } else {
-                       /* Temporarily unlock the registry lock. */
-                       mutex_unlock(&rcu_registry_lock);
-                       if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS)
+                       if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
+                               /* wait_gp unlocks/locks registry lock. */
                                wait_gp();
-                       else
+                       } else {
+                               /* Temporarily unlock the registry lock. */
+                               mutex_unlock(&rcu_registry_lock);
                                caa_cpu_relax();
-                       /* Re-lock the registry lock before the next loop. */
-                       mutex_lock(&rcu_registry_lock);
+                               /*
+                                * Re-lock the registry lock before the
+                                * next loop.
+                                */
+                               mutex_lock(&rcu_registry_lock);
+                       }
                }
 #else /* #ifndef HAS_INCOHERENT_CACHES */
                /*
@@ -341,16 +351,20 @@ static void wait_for_readers(struct cds_list_head *input_readers,
                                smp_mb_master(RCU_MB_GROUP);
                                wait_gp_loops = 0;
                        }
-                       /* Temporarily unlock the registry lock. */
-                       mutex_unlock(&rcu_registry_lock);
                        if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
+                               /* wait_gp unlocks/locks registry lock. */
                                wait_gp();
                                wait_gp_loops++;
                        } else {
+                               /* Temporarily unlock the registry lock. */
+                               mutex_unlock(&rcu_registry_lock);
                                caa_cpu_relax();
+                               /*
+                                * Re-lock the registry lock before the
+                                * next loop.
+                                */
+                               mutex_lock(&rcu_registry_lock);
                        }
-                       /* Re-lock the registry lock before the next loop. */
-                       mutex_lock(&rcu_registry_lock);
                }
 #endif /* #else #ifndef HAS_INCOHERENT_CACHES */
        }