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authorNick Piggin <nickpiggin@yahoo.com.au>2005-05-05 16:15:46 -0700
committerLinus Torvalds <torvalds@ppc970.osdl.org>2005-05-05 16:36:40 -0700
commitad576e63e0c8b274a8558b8e05a6d0526e804dc0 (patch)
treea7c44175df405cf2851f45a486ff96037d1a43e6 /fs/buffer.c
parentf3ddbdc6267c32223035ea9bb8456a2d86f65ba1 (diff)
[PATCH] __block_write_full_page race fix
When running fsstress -v -d $DIR/tmp -n 1000 -p 1000 -l 2 on an ext2 filesystem with 1024 byte block size, on SMP i386 with 4096 byte page size over loopback to an image file on a tmpfs filesystem, I would very quickly hit BUG_ON(!buffer_async_write(bh)); in fs/buffer.c:end_buffer_async_write It seems that more than one request would be submitted for a given bh at a time. What would happen is the following: 2 threads doing __mpage_writepages on the same page. Thread 1 - lock the page first, and enter __block_write_full_page. Thread 1 - (eg.) mark_buffer_async_write on the first 2 buffers. Thread 1 - set page writeback, unlock page. Thread 2 - lock page, wait on page writeback Thread 1 - submit_bh on the first 2 buffers. => both requests complete, none of the page buffers are async_write, end_page_writeback is called. Thread 2 - wakes up. enters __block_write_full_page. Thread 2 - mark_buffer_async_write on (eg.) the last buffer Thread 1 - finds the last buffer has async_write set, submit_bh on that. Thread 2 - submit_bh on the last buffer. => oops. So change __block_write_full_page to explicitly keep track of the last bh we need to issue, so we don't touch anything after issuing the last request. Signed-off-by: Nick Piggin <nickpiggin@yahoo.com.au> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Diffstat (limited to 'fs/buffer.c')
-rw-r--r--fs/buffer.c18
1 files changed, 13 insertions, 5 deletions
diff --git a/fs/buffer.c b/fs/buffer.c
index af7c51ded2e..bc75f2e7b27 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -1751,7 +1751,7 @@ static int __block_write_full_page(struct inode *inode, struct page *page,
int err;
sector_t block;
sector_t last_block;
- struct buffer_head *bh, *head;
+ struct buffer_head *bh, *head, *last_bh = NULL;
int nr_underway = 0;
BUG_ON(!PageLocked(page));
@@ -1809,7 +1809,6 @@ static int __block_write_full_page(struct inode *inode, struct page *page,
} while (bh != head);
do {
- get_bh(bh);
if (!buffer_mapped(bh))
continue;
/*
@@ -1827,6 +1826,8 @@ static int __block_write_full_page(struct inode *inode, struct page *page,
}
if (test_clear_buffer_dirty(bh)) {
mark_buffer_async_write(bh);
+ get_bh(bh);
+ last_bh = bh;
} else {
unlock_buffer(bh);
}
@@ -1845,10 +1846,13 @@ static int __block_write_full_page(struct inode *inode, struct page *page,
if (buffer_async_write(bh)) {
submit_bh(WRITE, bh);
nr_underway++;
+ put_bh(bh);
+ if (bh == last_bh)
+ break;
}
- put_bh(bh);
bh = next;
} while (bh != head);
+ bh = head;
err = 0;
done:
@@ -1887,10 +1891,11 @@ recover:
bh = head;
/* Recovery: lock and submit the mapped buffers */
do {
- get_bh(bh);
if (buffer_mapped(bh) && buffer_dirty(bh)) {
lock_buffer(bh);
mark_buffer_async_write(bh);
+ get_bh(bh);
+ last_bh = bh;
} else {
/*
* The buffer may have been set dirty during
@@ -1909,10 +1914,13 @@ recover:
clear_buffer_dirty(bh);
submit_bh(WRITE, bh);
nr_underway++;
+ put_bh(bh);
+ if (bh == last_bh)
+ break;
}
- put_bh(bh);
bh = next;
} while (bh != head);
+ bh = head;
goto done;
}