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Date: Tue, 1 Feb 2011 09:51:26 -0800
From: Curt Wohlgemuth <curtw@...gle.com>
To: ext4 development <linux-ext4@...r.kernel.org>
Subject: ext4: Fix data corruption with multi-block writepages support
This fixes a corruption problem with the multi-block
writepages submittal change for ext4, from commit
bd2d0210cf22f2bd0cef72eb97cf94fc7d31d8cc ("ext4: use bio
layer instead of buffer layer in mpage_da_submit_io").
(Note that this corruption is not present in 2.6.37 on ext4,
because the multi-block writepages function is only enabled
by a non-default mount option. With the patch below, we can
eventually remove this mount option.)
The ext4 code path to bundle multiple pages for writeback in
ext4_bio_write_page() had a bug: we should be clearing
buffer head dirty flags *before* we submit the bio, not in
the completion routine.
The patch below was tested on 2.6.37 under KVM with the
postgresql script specified by Ted Tso in
1449032be17abb69116dbc393f67ceb8bd034f92 -- without this
commit, and hence by default using the multiblock writepages
submittal code.
Without the patch, I'd hit the corruption problem about
50-70% of the time. With the patch, I executed the script
> 100 times with no corruption seen.
Also don't dereference the bio in ext4_end_bio() after the
bio_put() call.
(I also added a blank line in ext4_bio_write_page(), 'cause
my eyes constantly confused the complex 'for' conditions
from the first statement in the block.)
Signed-off-by: Curt Wohlgemuth <curtw@...gle.com>
---
diff --git a/fs/ext4/page-io.c b/fs/ext4/page-io.c
index 6e0e99b..c3d490f 100644
--- a/fs/ext4/page-io.c
+++ b/fs/ext4/page-io.c
@@ -193,6 +193,7 @@ static void ext4_end_bio(struct bio *bio, int error)
struct inode *inode;
unsigned long flags;
int i;
+ sector_t bi_sector = bio->bi_sector;
BUG_ON(!io_end);
bio->bi_private = NULL;
@@ -210,9 +211,7 @@ static void ext4_end_bio(struct bio *bio, int error)
if (error)
SetPageError(page);
BUG_ON(!head);
- if (head->b_size == PAGE_CACHE_SIZE)
- clear_buffer_dirty(head);
- else {
+ if (head->b_size != PAGE_CACHE_SIZE) {
loff_t offset;
loff_t io_end_offset = io_end->offset + io_end->size;
@@ -224,7 +223,6 @@ static void ext4_end_bio(struct bio *bio, int error)
if (error)
buffer_io_error(bh);
- clear_buffer_dirty(bh);
}
if (buffer_delay(bh))
partial_write = 1;
@@ -260,7 +258,7 @@ static void ext4_end_bio(struct bio *bio, int error)
(unsigned long long) io_end->offset,
(long) io_end->size,
(unsigned long long)
- bio->bi_sector >> (inode->i_blkbits - 9));
+ bi_sector >> (inode->i_blkbits - 9));
}
/* Add the io_end to per-inode completed io list*/
@@ -383,6 +381,7 @@ int ext4_bio_write_page(struct ext4_io_submit *io,
blocksize = 1 << inode->i_blkbits;
+ BUG_ON(!PageLocked(page));
BUG_ON(PageWriteback(page));
set_page_writeback(page);
ClearPageError(page);
@@ -400,12 +399,14 @@ int ext4_bio_write_page(struct ext4_io_submit *io,
for (bh = head = page_buffers(page), block_start = 0;
bh != head || !block_start;
block_start = block_end, bh = bh->b_this_page) {
+
block_end = block_start + blocksize;
if (block_start >= len) {
clear_buffer_dirty(bh);
set_buffer_uptodate(bh);
continue;
}
+ clear_buffer_dirty(bh);
ret = io_submit_add_bh(io, io_page, inode, wbc, bh);
if (ret) {
/*
--
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