[PATCH] JFS: Fix race waking up jfsIO kernel thread

[Dave Kleikamp <shaggy@linux.vnet.ibm.com>]

I've been looking at a hang that was reported off-list, and I believe I
found the cause.  I'm still waiting for confirmation on whether the
patch does fix the problem, but I wanted to distribute the patch in case
anyone else is seeing a similar hang.  It looks like the problem is in
kernels from 2.6.17 to the present.

Thanks,
Shaggy

JFS: Fix race waking up jfsIO kernel thread

It's possible for a journal I/O request to be added to the log_redrive
queue and the jfsIO thread to be awakened after the thread releases
log_redrive_lock but before it sets its state to TASK_INTERRUPTIBLE.

The jfsIO thread should set its state before giving up the spinlock, so
the waking thread will really wake it.

Signed-off-by: Dave Kleikamp <shaggy@linux.vnet.ibm.com>

diff --git a/fs/jfs/jfs_logmgr.c b/fs/jfs/jfs_logmgr.c
index ff7f1be..16c6268 100644
--- a/fs/jfs/jfs_logmgr.c
+++ b/fs/jfs/jfs_logmgr.c
@@ -2354,12 +2354,13 @@ int jfsIOWait(void *arg)
 			lbmStartIO(bp);
 			spin_lock_irq(&log_redrive_lock);
 		}
-		spin_unlock_irq(&log_redrive_lock);
 
 		if (freezing(current)) {
+			spin_unlock_irq(&log_redrive_lock);
 			refrigerator();
 		} else {
 			set_current_state(TASK_INTERRUPTIBLE);
+			spin_unlock_irq(&log_redrive_lock);
 			schedule();
 			__set_current_state(TASK_RUNNING);
 		}

-- 
David Kleikamp
IBM Linux Technology Center