fs/direct-io.c: don't try to allocate more than BIO_MAX_PAGES in a bio

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>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/fs/direct-io.c b/fs/direct-io.c
index 85882f6ba5f73c66b614a79ad3594a3dab5dc2b0..b044705eedd4f0836cbcbe5d0f92bf6fb6e39cf7 100644 (file)
--- a/fs/direct-io.c
+++ b/fs/direct-io.c
@@ -325,12 +325,16 @@ void dio_end_io(struct bio *bio, int error)
 }
 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 block_device *bdev,
 
        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, sector_t start_sector)
                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;