From eb9c36973cc92e2f0d1a45d511bf1e7c1eccc508 Mon Sep 17 00:00:00 2001
From: yangsheng <yangsheng>
Date: Fri, 13 Feb 2009 14:50:01 +0000
Subject: [PATCH] Branch b1_6 b=16579

i=shadow, zhen.liang

Use RCU lock to enable stack dump.
---
 lnet/autoconf/lustre-lnet.m4 | 19 +++++++++++++++++++
 lnet/libcfs/watchdog.c       | 23 +++++++++++++----------
 2 files changed, 32 insertions(+), 10 deletions(-)

diff --git a/lnet/autoconf/lustre-lnet.m4 b/lnet/autoconf/lustre-lnet.m4
index a9bbaf1..5ca3cfc 100644
--- a/lnet/autoconf/lustre-lnet.m4
+++ b/lnet/autoconf/lustre-lnet.m4
@@ -1188,6 +1188,24 @@ LB_LINUX_TRY_COMPILE([
 ])
 
 
+# check if task_struct with rcu memeber
+AC_DEFUN([LN_TASK_RCU],
+[AC_MSG_CHECKING([if task_struct has a rcu field])
+LB_LINUX_TRY_COMPILE([
+	#include <linux/sched.h>
+],[
+        struct task_struct tsk;
+
+        tsk.rcu.next = NULL;
+],[
+	AC_MSG_RESULT([yes])
+        AC_DEFINE(HAVE_TASK_RCU, 1,
+                  [task_struct has rcu field])
+],[
+	AC_MSG_RESULT([no])
+])
+])
+
 # LN_TASKLIST_LOCK
 # 2.6.18 remove tasklist_lock export
 AC_DEFUN([LN_TASKLIST_LOCK],
@@ -1409,6 +1427,7 @@ LN_U64_LONG_LONG
 LN_SSIZE_T_LONG
 LN_SIZE_T_LONG
 LN_LE_TYPES
+LN_TASK_RCU
 # 2.6.18
 LN_TASKLIST_LOCK
 # 2.6.19
diff --git a/lnet/libcfs/watchdog.c b/lnet/libcfs/watchdog.c
index b007c28..92f3565 100644
--- a/lnet/libcfs/watchdog.c
+++ b/lnet/libcfs/watchdog.c
@@ -102,14 +102,20 @@ static cfs_time_t lcw_last_watchdog_time;
 static int lcw_recent_watchdog_count;
 static spinlock_t lcw_last_watchdog_lock = SPIN_LOCK_UNLOCKED;
 
-#ifdef HAVE_TASKLIST_LOCK
 static void
 lcw_dump(struct lc_watchdog *lcw)
 {
         cfs_task_t *tsk;
+#if defined(HAVE_TASKLIST_LOCK)
+        read_lock(&tasklist_lock);
+#elif defined(HAVE_TASK_RCU)
+        rcu_read_lock();
+#else
+        CERROR("unable to dump stack because of missing export\n"); 
+        return;
+#endif
         ENTRY;
 
-        read_lock(&tasklist_lock);
         tsk = find_task_by_pid(lcw->lcw_pid);
 
         if (tsk == NULL) {
@@ -121,17 +127,14 @@ lcw_dump(struct lc_watchdog *lcw)
         } else {
                 libcfs_debug_dumpstack(tsk);
         }
-        
+
+#if defined(HAVE_TASKLIST_LOCK)
         read_unlock(&tasklist_lock);
+#elif defined(HAVE_TASK_RCU)
+        rcu_read_unlock();
+#endif
         EXIT;
 }
-#else
-static void
-lcw_dump(struct lc_watchdog *lcw)
-{
-        CERROR("unable to dump stack because of missing export\n");
-}
-#endif
 
 static void lcw_cb(unsigned long data)
 {
-- 
1.8.3.1