Re: writeback hang in current mainline

[Jens Axboe <jens.axboe@oracle.com>]

On Wed, May 26 2010, Christoph Hellwig wrote:
> On Wed, May 26, 2010 at 01:21:25PM +0200, Jens Axboe wrote:
> > Not good, can you see if reverting 7c8a3554 makes it go away?
> 
> Reverting back to the revision before 7c8a3554 gives me lots of warnings ala:
> 
> [  178.253431] ------------[ cut here ]------------
> [  178.256845] WARNING: at
> /home/hch/work/linux-2.6/fs/fs-writeback.c:596
> writeback_inodes_wb+0x423/0x440()
> [  178.259995] Hardware name: Bochs
> [  178.261270] Modules linked in:
> [  178.262508] Pid: 2298, comm: flush-253:16 Tainted: G        W
> 2.6.34-rc5 #121
> [  178.265199] Call Trace:
> [  178.266210]  [<c08d86ca>] ? printk+0x18/0x1a
> [  178.267597]  [<c0162d0d>] warn_slowpath_common+0x6d/0xa0
> [  178.269296]  [<c0216ff3>] ? writeback_inodes_wb+0x423/0x440
> [  178.271348]  [<c0216ff3>] ? writeback_inodes_wb+0x423/0x440
> [  178.273121]  [<c0162d55>] warn_slowpath_null+0x15/0x20
> [  178.274681]  [<c0216ff3>] writeback_inodes_wb+0x423/0x440
> [  178.276390]  [<c0217111>] wb_writeback+0x101/0x1b0
> [  178.277846]  [<c01a9a79>] ? __call_rcu+0x99/0x130
> [  178.279287]  [<c01a9b38>] ? call_rcu+0x8/0x10
> [  178.281110]  [<c02161fa>] ? wb_clear_pending+0x7a/0xa0
> [  178.282673]  [<c021728f>] wb_do_writeback+0xcf/0x1a0
> [  178.284239]  [<c02171e0>] ? wb_do_writeback+0x20/0x1a0
> [  178.285823]  [<c021738a>] bdi_writeback_task+0x2a/0x90
> [  178.287371]  [<c01dca90>] ? bdi_start_fn+0x0/0xb0
> [  178.288992]  [<c01dcae8>] bdi_start_fn+0x58/0xb0
> [  178.290823]  [<c01dca90>] ? bdi_start_fn+0x0/0xb0
> [  178.292378]  [<c017dc7c>] kthread+0x6c/0x80
> [  178.293711]  [<c017dc10>] ? kthread+0x0/0x80
> [  178.295073]  [<c013023a>] kernel_thread_helper+0x6/0x1c
> [  178.296753] ---[ end trace a7919e7f17c0a80f ]---

Oops yes, you need to revert the parent too. But nevermind, I think I
see the issue. Can you try the below (go back to -git again)?

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index ea8592b..5e6cc61 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -121,6 +121,7 @@ static void bdi_work_free(struct rcu_head *head)
 static void wb_work_complete(struct bdi_work *work)
 {
 	const enum writeback_sync_modes sync_mode = work->args.sync_mode;
+	const int caller_frees = work->args.sb_pinned;
 	int onstack = bdi_work_on_stack(work);
 
 	/*
@@ -131,7 +132,7 @@ static void wb_work_complete(struct bdi_work *work)
 	 */
 	if (!onstack)
 		bdi_work_clear(work);
-	if (sync_mode == WB_SYNC_NONE || onstack)
+	if ((sync_mode == WB_SYNC_NONE && caller_frees) || onstack)
 		call_rcu(&work->rcu_head, bdi_work_free);
 }
 
@@ -206,8 +207,10 @@ static void bdi_alloc_queue_work(struct backing_dev_info *bdi,
 	if (work) {
 		bdi_work_init(work, args);
 		bdi_queue_work(bdi, work);
-		if (wait)
+		if (wait) {
 			bdi_wait_on_work_clear(work);
+			kfree(work);
+		}
 	} else {
 		struct bdi_writeback *wb = &bdi->wb;
 

-- 
Jens Axboe