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

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

This patch fixes a deadlock that has been reported by three different
users on recent kernels.  The problem exists on mainline kernels since
2.6.18.  It is included in linux-2.6.22-rc1.

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 the 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 -Nurp linux-2.6.21.1/fs/jfs/jfs_logmgr.c linux/fs/jfs/jfs_logmgr.c
--- linux-2.6.21.1/fs/jfs/jfs_logmgr.c	2007-04-27 16:49:26.000000000 -0500
+++ linux/fs/jfs/jfs_logmgr.c	2007-05-15 22:39:31.000000000 -0500
@@ -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();
 			current->state = TASK_RUNNING;
 		}

-- 
David Kleikamp
IBM Linux Technology Center

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