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Subject[patch] __block_write_full_page bug
Another buffer bug :(

--
SUSE Labs, Novell Inc.
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. __block_write_full_page looks like the culprit - with the
following patch things are very stable.

Signed-off-by: Nick Piggin <nickpiggin@yahoo.com.au>

Index: linux-2.6/fs/buffer.c
===================================================================
--- linux-2.6.orig/fs/buffer.c 2005-04-25 13:13:37.000000000 +1000
+++ linux-2.6/fs/buffer.c 2005-04-25 13:14:52.000000000 +1000
@@ -1750,8 +1750,9 @@ static int __block_write_full_page(struc
int err;
sector_t block;
sector_t last_block;
- struct buffer_head *bh, *head;
- int nr_underway = 0;
+ struct buffer_head *bh, *head, *arr[MAX_BUF_PER_PAGE];
+ int idx = 0;
+ int nr_underway;

BUG_ON(!PageLocked(page));

@@ -1826,6 +1827,7 @@ static int __block_write_full_page(struc
}
if (test_clear_buffer_dirty(bh)) {
mark_buffer_async_write(bh);
+ arr[idx++] = bh;
} else {
unlock_buffer(bh);
}
@@ -1839,15 +1841,12 @@ static int __block_write_full_page(struc
set_page_writeback(page);
unlock_page(page);

- do {
- struct buffer_head *next = bh->b_this_page;
- if (buffer_async_write(bh)) {
+ for (nr_underway = 0; nr_underway < idx; nr_underway++) {
+ bh = arr[nr_underway];
+ if (buffer_async_write(bh))
submit_bh(WRITE, bh);
- nr_underway++;
- }
put_bh(bh);
- bh = next;
- } while (bh != head);
+ }

err = 0;
done:
@@ -1890,6 +1889,7 @@ recover:
if (buffer_mapped(bh) && buffer_dirty(bh)) {
lock_buffer(bh);
mark_buffer_async_write(bh);
+ arr[idx++] = bh;
} else {
/*
* The buffer may have been set dirty during
@@ -1902,16 +1902,14 @@ recover:
BUG_ON(PageWriteback(page));
set_page_writeback(page);
unlock_page(page);
- do {
- struct buffer_head *next = bh->b_this_page;
+ for (nr_underway = 0; nr_underway < idx; nr_underway++) {
+ bh = arr[nr_underway];
if (buffer_async_write(bh)) {
clear_buffer_dirty(bh);
submit_bh(WRITE, bh);
- nr_underway++;
}
put_bh(bh);
- bh = next;
- } while (bh != head);
+ }
goto done;
}

@@ -2741,6 +2739,7 @@ sector_t generic_block_bmap(struct addre
static int end_bio_bh_io_sync(struct bio *bio, unsigned int bytes_done, int err)
{
struct buffer_head *bh = bio->bi_private;
+ bh_end_io_t *end_fn;

if (bio->bi_size)
return 1;
@@ -2750,7 +2749,16 @@ static int end_bio_bh_io_sync(struct bio
set_bit(BH_Eopnotsupp, &bh->b_state);
}

- bh->b_end_io(bh, test_bit(BIO_UPTODATE, &bio->bi_flags));
+ end_fn = bh->b_end_io;
+
+ /*
+ * These two lines are debugging only - make sure b_end_io
+ * isn't run twice for the same io request.
+ */
+ BUG_ON(!end_fn);
+ bh->b_end_io = NULL;
+
+ end_fn(bh, test_bit(BIO_UPTODATE, &bio->bi_flags));
bio_put(bio);
return 0;
}
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