[PATCH] DIO pages-in-io accounting fix

I found one more accounting inconsistency with dio_pages_in_io.  This is a
day-one bug and I started hitting it on latest -mm due to the recent
changes to dio_pages_in_io calculations to be exact.

If the file is badly fragmented (no contiguous blocks at all), and the user
buffer is not page aligned - we need to create IO for each disk block with
2 pages.  (bio with 2 vecs).

dio_bio_add_page() should not decrement dio_pages_in_io for every add page.
 It should only decrement, it only if its done with that page and moving on
to next page.  (since dio_pages_in_io represent how many actual pages we
are operating on).

Here is the patch to fix this accounting.  Without this patch, we will hit
BUG() in dio_new_bio() with O_DIRECT on filesystems.

Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

diff --git a/fs/direct-io.c b/fs/direct-io.c
index 20405c7844999dfe5d14d456603dcefbd2bdd032..276905778c00febf793b33bc6c153d9d57427f15 100644 (file)
--- a/fs/direct-io.c
+++ b/fs/direct-io.c
@@ -561,7 +561,11 @@ static int dio_bio_add_page(struct dio *dio)
        ret = bio_add_page(dio->bio, dio->cur_page,
                        dio->cur_page_len, dio->cur_page_offset);
        if (ret == dio->cur_page_len) {
-               dio->pages_in_io--;
+               /*
+                * Decrement count only, if we are done with this page
+                */
+               if ((dio->cur_page_len + dio->cur_page_offset) == PAGE_SIZE)
+                       dio->pages_in_io--;
                page_cache_get(dio->cur_page);
                dio->final_block_in_bio = dio->cur_page_block +
                        (dio->cur_page_len >> dio->blkbits);