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Subject[patch 137/176] fs/direct-io.c: dont try to allocate more than BIO_MAX_PAGES in a bio
2.6.36-stable review patch.  If anyone has any objections, please let us know.

------------------

From: David Dillow <dillowda@ornl.gov>

commit 20d9600cb407b0b55fef6ee814b60345c6f58264 upstream.

When using devices that support max_segments > BIO_MAX_PAGES (256), direct
IO tries to allocate a bio with more pages than allowed, which leads to an
oops in dio_bio_alloc(). Clamp the request to the supported maximum, and
change dio_bio_alloc() to reflect that bio_alloc() will always return a
bio when called with __GFP_WAIT and a valid number of vectors.

[akpm@linux-foundation.org: remove redundant BUG_ON()]
Signed-off-by: David Dillow <dillowda@ornl.gov>
Reviewed-by: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
fs/direct-io.c | 10 +++++++---
1 file changed, 7 insertions(+), 3 deletions(-)

--- a/fs/direct-io.c
+++ b/fs/direct-io.c
@@ -325,12 +325,16 @@ void dio_end_io(struct bio *bio, int err
}
EXPORT_SYMBOL_GPL(dio_end_io);

-static int
+static void
dio_bio_alloc(struct dio *dio, struct block_device *bdev,
sector_t first_sector, int nr_vecs)
{
struct bio *bio;

+ /*
+ * bio_alloc() is guaranteed to return a bio when called with
+ * __GFP_WAIT and we request a valid number of vectors.
+ */
bio = bio_alloc(GFP_KERNEL, nr_vecs);

bio->bi_bdev = bdev;
@@ -342,7 +346,6 @@ dio_bio_alloc(struct dio *dio, struct bl

dio->bio = bio;
dio->logical_offset_in_bio = dio->cur_page_fs_offset;
- return 0;
}

/*
@@ -583,8 +586,9 @@ static int dio_new_bio(struct dio *dio,
goto out;
sector = start_sector << (dio->blkbits - 9);
nr_pages = min(dio->pages_in_io, bio_get_nr_vecs(dio->map_bh.b_bdev));
+ nr_pages = min(nr_pages, BIO_MAX_PAGES);
BUG_ON(nr_pages <= 0);
- ret = dio_bio_alloc(dio, dio->map_bh.b_bdev, sector, nr_pages);
+ dio_bio_alloc(dio, dio->map_bh.b_bdev, sector, nr_pages);
dio->boundary = 0;
out:
return ret;



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