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authorNick Piggin <npiggin@suse.de>2009-09-15 21:37:55 +0200
committerJens Axboe <jens.axboe@oracle.com>2009-09-16 15:18:53 +0200
commit1ef7d9aa32a8ee054c4d4fdcd2ea537c04d61b2f (patch)
tree69c570a78f37760ead0c8cad2eda25991c3fcd4c
parent77b9d059cb3ddb8b1246d5878e81d52926550b23 (diff)
writeback: fix possible bdi writeback refcounting problem
wb_clear_pending AFAIKS should not be called after the item has been put on the list, except by the worker threads. It could lead to the situation where the refcount is decremented below 0 and cause lots of problems. Presumably the !wb_has_dirty_io case is not a common one, so it can be discovered when the thread wakes up to check? Also add a comment in bdi_work_clear. Signed-off-by: Nick Piggin <npiggin@suse.de> Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
-rw-r--r--fs/fs-writeback.c13
1 files changed, 6 insertions, 7 deletions
diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 7eba7326b9b..8e1e5e19d21 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -97,6 +97,11 @@ static void bdi_work_clear(struct bdi_work *work)
{
clear_bit(WS_USED_B, &work->state);
smp_mb__after_clear_bit();
+ /*
+ * work can have disappeared at this point. bit waitq functions
+ * should be able to tolerate this, provided bdi_sched_wait does
+ * not dereference it's pointer argument.
+ */
wake_up_bit(&work->state, WS_USED_B);
}
@@ -169,13 +174,7 @@ static void bdi_queue_work(struct backing_dev_info *bdi, struct bdi_work *work)
else {
struct bdi_writeback *wb = &bdi->wb;
- /*
- * End work now if this wb has no dirty IO pending. Otherwise
- * wakeup the handling thread
- */
- if (!wb_has_dirty_io(wb))
- wb_clear_pending(wb, work);
- else if (wb->task)
+ if (wb->task)
wake_up_process(wb->task);
}
}