Re: prepare_to_wait/waitqueue_active issues in 2.6

[Anton Blanchard <anton@samba.org>]

> End result is waitqueue_active returns 0 and buffer_locked returns 1.
> We miss a wakeup. Game over. Ive attached a patch that forces the check
> to happen after we are put on the waitqueue. Thanks to Brian Twichell
> for the analysis and suggested fix for this.

This time for sure.

Anton

===== mm/filemap.c 1.212 vs edited =====
--- 1.212/mm/filemap.c	Sun Oct 26 16:41:06 2003
+++ edited/mm/filemap.c	Sun Dec 14 14:25:45 2003
@@ -299,6 +299,7 @@
 
 	do {
 		prepare_to_wait(waitqueue, &wait, TASK_UNINTERRUPTIBLE);
+		smp_mb();
 		if (test_bit(bit_nr, &page->flags)) {
 			sync_page(page);
 			io_schedule();
@@ -372,6 +373,7 @@
 
 	while (TestSetPageLocked(page)) {
 		prepare_to_wait(wqh, &wait, TASK_UNINTERRUPTIBLE);
+		smp_mb();
 		if (PageLocked(page)) {
 			sync_page(page);
 			io_schedule();
===== fs/buffer.c 1.215 vs edited =====
--- 1.215/fs/buffer.c	Tue Sep 30 11:12:02 2003
+++ edited/fs/buffer.c	Sun Dec 14 14:24:26 2003
@@ -131,6 +131,7 @@
 
 	do {
 		prepare_to_wait(wqh, &wait, TASK_UNINTERRUPTIBLE);
+		smp_mb();
 		if (buffer_locked(bh)) {
 			blk_run_queues();
 			io_schedule();