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authorAneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>2009-06-14 17:57:10 -0400
committerTheodore Ts'o <tytso@mit.edu>2009-06-14 17:57:10 -0400
commitc364b22c9580a885e0f8c0d0f9710d67dc448958 (patch)
tree6a714e767afb7d08a648f8e23e4acca414896699 /fs
parentb767e78a179e5ab30fdbff1686d074ac270471eb (diff)
ext4: Fix mmap/truncate race when blocksize < pagesize && delayed allocation
It is possible to see buffer_heads which are not mapped in the writepage callback in the following scneario (where the fs blocksize is 1k and the page size is 4k): 1) truncate(f, 1024) 2) mmap(f, 0, 4096) 3) a[0] = 'a' 4) truncate(f, 4096) 5) writepage(...) Now if we get a writepage callback immediately after (4) and before an attempt to write at any other offset via mmap address (which implies we are yet to get a pagefault and do a get_block) what we would have is the page which is dirty have first block allocated and the other three buffer_heads unmapped. In the above case the writepage should go ahead and try to write the first blocks and clear the page_dirty flag. Further attempts to write to the page will again create a fault and result in allocating blocks and marking page dirty. If we don't write any other offset via mmap address we would still have written the first block to the disk and rest of the space will be considered as a hole. So to address this, we change all of the places where we look for delayed, unmapped, or unwritten buffer heads, and only check for delayed or unwritten buffer heads instead. Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com> Acked-by: Jan Kara <jack@suse.cz> Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Diffstat (limited to 'fs')
-rw-r--r--fs/ext4/inode.c23
1 files changed, 8 insertions, 15 deletions
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index b87b68cd324..1275f34589c 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -2305,15 +2305,9 @@ flush_it:
return;
}
-static int ext4_bh_unmapped_or_delay(handle_t *handle, struct buffer_head *bh)
+static int ext4_bh_delay_or_unwritten(handle_t *handle, struct buffer_head *bh)
{
- /*
- * unmapped buffer is possible for holes.
- * delay buffer is possible with delayed allocation.
- * We also need to consider unwritten buffer as unmapped.
- */
- return (!buffer_mapped(bh) || buffer_delay(bh) ||
- buffer_unwritten(bh)) && buffer_dirty(bh);
+ return (buffer_delay(bh) || buffer_unwritten(bh)) && buffer_dirty(bh);
}
/*
@@ -2400,7 +2394,7 @@ static int __mpage_da_writepage(struct page *page,
* Otherwise we won't make progress
* with the page in ext4_da_writepage
*/
- if (ext4_bh_unmapped_or_delay(NULL, bh)) {
+ if (ext4_bh_delay_or_unwritten(NULL, bh)) {
mpage_add_bh_to_extent(mpd, logical,
bh->b_size,
bh->b_state);
@@ -2517,7 +2511,6 @@ static int noalloc_get_block_write(struct inode *inode, sector_t iblock,
* so call get_block_wrap with create = 0
*/
ret = ext4_get_blocks(NULL, inode, iblock, max_blocks, bh_result, 0);
- BUG_ON(create && ret == 0);
if (ret > 0) {
bh_result->b_size = (ret << inode->i_blkbits);
ret = 0;
@@ -2533,7 +2526,7 @@ static int noalloc_get_block_write(struct inode *inode, sector_t iblock,
* - grab_page_cache when doing write_begin (have journal handle)
*/
static int ext4_da_writepage(struct page *page,
- struct writeback_control *wbc)
+ struct writeback_control *wbc)
{
int ret = 0;
loff_t size;
@@ -2551,7 +2544,7 @@ static int ext4_da_writepage(struct page *page,
if (page_has_buffers(page)) {
page_bufs = page_buffers(page);
if (walk_page_buffers(NULL, page_bufs, 0, len, NULL,
- ext4_bh_unmapped_or_delay)) {
+ ext4_bh_delay_or_unwritten)) {
/*
* We don't want to do block allocation
* So redirty the page and return
@@ -2584,7 +2577,7 @@ static int ext4_da_writepage(struct page *page,
page_bufs = page_buffers(page);
/* check whether all are mapped and non delay */
if (walk_page_buffers(NULL, page_bufs, 0, len, NULL,
- ext4_bh_unmapped_or_delay)) {
+ ext4_bh_delay_or_unwritten)) {
redirty_page_for_writepage(wbc, page);
unlock_page(page);
return 0;
@@ -3232,7 +3225,7 @@ static int ext4_normal_writepage(struct page *page,
* happily proceed with mapping them and writing the page.
*/
BUG_ON(walk_page_buffers(NULL, page_buffers(page), 0, len, NULL,
- ext4_bh_unmapped_or_delay));
+ ext4_bh_delay_or_unwritten));
}
if (!ext4_journal_current_handle())
@@ -3322,7 +3315,7 @@ static int ext4_journalled_writepage(struct page *page,
* happily proceed with mapping them and writing the page.
*/
BUG_ON(walk_page_buffers(NULL, page_buffers(page), 0, len, NULL,
- ext4_bh_unmapped_or_delay));
+ ext4_bh_delay_or_unwritten));
}
if (ext4_journal_current_handle())