ocfs2: Concurrent access of o2hb_region->hr_task was not locked

This means that a build-up and a teardown could race which would result in a
double-kthread_stop().

Protect the setting and clearing of hr_task with o2hb_live_lock, as it's not
a common thing and not performance critical.

Signed-off-by: Joel Becker <joel.becker@oracle.com>
Signed-off-by: Mark Fasheh <mark.fasheh@oracle.com>

diff --git a/fs/ocfs2/cluster/heartbeat.c b/fs/ocfs2/cluster/heartbeat.c
index 0f2cfecd42c0bbeeed02ee7dd4dad9ca7da1978c..eba282da500e7215839d8db128ff14938be9d21d 100644 (file)
--- a/fs/ocfs2/cluster/heartbeat.c
+++ b/fs/ocfs2/cluster/heartbeat.c
@@ -1234,6 +1234,7 @@ static ssize_t o2hb_region_dev_write(struct o2hb_region *reg,
                                     const char *page,
                                     size_t count)
 {
+       struct task_struct *hb_task;
        long fd;
        int sectsize;
        char *p = (char *)page;
@@ -1319,20 +1320,28 @@ static ssize_t o2hb_region_dev_write(struct o2hb_region *reg,
         */
        atomic_set(&reg->hr_steady_iterations, O2HB_LIVE_THRESHOLD + 1);
 
-       reg->hr_task = kthread_run(o2hb_thread, reg, "o2hb-%s",
-                                  reg->hr_item.ci_name);
-       if (IS_ERR(reg->hr_task)) {
-               ret = PTR_ERR(reg->hr_task);
+       hb_task = kthread_run(o2hb_thread, reg, "o2hb-%s",
+                             reg->hr_item.ci_name);
+       if (IS_ERR(hb_task)) {
+               ret = PTR_ERR(hb_task);
                mlog_errno(ret);
-               reg->hr_task = NULL;
                goto out;
        }
 
+       spin_lock(&o2hb_live_lock);
+       reg->hr_task = hb_task;
+       spin_unlock(&o2hb_live_lock);
+
        ret = wait_event_interruptible(o2hb_steady_queue,
                                atomic_read(&reg->hr_steady_iterations) == 0);
        if (ret) {
-               kthread_stop(reg->hr_task);
+               spin_lock(&o2hb_live_lock);
+               hb_task = reg->hr_task;
                reg->hr_task = NULL;
+               spin_unlock(&o2hb_live_lock);
+
+               if (hb_task)
+                       kthread_stop(hb_task);
                goto out;
        }
 
@@ -1354,10 +1363,17 @@ out:
 static ssize_t o2hb_region_pid_read(struct o2hb_region *reg,
                                       char *page)
 {
-       if (!reg->hr_task)
+       pid_t pid = 0;
+
+       spin_lock(&o2hb_live_lock);
+       if (reg->hr_task)
+               pid = reg->hr_task->pid;
+       spin_unlock(&o2hb_live_lock);
+
+       if (!pid)
                return 0;
 
-       return sprintf(page, "%u\n", reg->hr_task->pid);
+       return sprintf(page, "%u\n", pid);
 }
 
 struct o2hb_region_attribute {
@@ -1495,13 +1511,17 @@ out:
 static void o2hb_heartbeat_group_drop_item(struct config_group *group,
                                           struct config_item *item)
 {
+       struct task_struct *hb_task;
        struct o2hb_region *reg = to_o2hb_region(item);
 
        /* stop the thread when the user removes the region dir */
-       if (reg->hr_task) {
-               kthread_stop(reg->hr_task);
-               reg->hr_task = NULL;
-       }
+       spin_lock(&o2hb_live_lock);
+       hb_task = reg->hr_task;
+       reg->hr_task = NULL;
+       spin_unlock(&o2hb_live_lock);
+
+       if (hb_task)
+               kthread_stop(hb_task);
 
        config_item_put(item);
 }