[PATCH] Fix try_to_free_buffer() locking
Fix commit ecdfc9787fe527491baefc22dce8b2dbd5b2908d
Not to put too fine a point on it, but in a nutshell...
__set_page_dirty_buffers() | try_to_free_buffers()
---------------------------+---------------------------
| spin_lock(private_lock);
| drop_bufers()
| spin_unlock(private_lock);
spin_lock(private_lock) |
!page_has_buffers() |
spin_unlock(private_lock) |
SetPageDirty() |
| cancel_dirty_page()
oops!
Signed-off-by: Nick Piggin <npiggin@suse.de>
Acked-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/fs/buffer.c b/fs/buffer.c
index 460f1c4..1ad674f 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -2844,7 +2844,6 @@
spin_lock(&mapping->private_lock);
ret = drop_buffers(page, &buffers_to_free);
- spin_unlock(&mapping->private_lock);
/*
* If the filesystem writes its buffers by hand (eg ext3)
@@ -2855,9 +2854,14 @@
* Also, during truncate, discard_buffer will have marked all
* the page's buffers clean. We discover that here and clean
* the page also.
+ *
+ * private_lock must be held over this entire operation in order
+ * to synchronise against __set_page_dirty_buffers and prevent the
+ * dirty bit from being lost.
*/
if (ret)
cancel_dirty_page(page, PAGE_CACHE_SIZE);
+ spin_unlock(&mapping->private_lock);
out:
if (buffers_to_free) {
struct buffer_head *bh = buffers_to_free;