bio: don't overflow in bio_get_nr_vecs()
bio: don't overflow in bio_get_nr_vecs()

There were two places bio_get_nr_vecs() could overflow:

First, it did a left shift to convert from sectors to bytes immediately
before dividing by PAGE_SIZE.  If PAGE_SIZE ever was less than 512 a great
many things would break, so dividing by PAGE_SIZE >> 9 is safe and will
generate smaller code too.

The nastier overflow was in the DIV_ROUND_UP() (that's what the code was
effectively doing, anyways).  If n + d overflowed, the whole thing would
return 0 which breaks things rather effectively.

bio_get_nr_vecs() doesn't claim to give an exact value anyways, so the
DIV_ROUND_UP() is silly; we could do a straight divide except if a
device's queue_max_sectors was less than PAGE_SIZE we'd return 0.  So we
just add 1; this should always be safe - things will break badly if
bio_get_nr_vecs() returns > BIO_MAX_PAGES (bio_alloc() will suddenly start
failing) but it's queue_max_segments that must guard against this, if
queue_max_sectors is preventing this from happen things are going to
explode on architectures with different PAGE_SIZE.

Signed-off-by: Kent Overstreet <8f464ad20d7f95b5ede78c4772dc4f5cc3ffa553@google.com>
Cc: Tejun Heo <546b05909706652891a87f7bfe385ae147f61f91@kernel.org>
Acked-by: Valdis Kletnieks <183bdd1d6873c97a167cc4b441324ddf7a94dd06@vt.edu>
Signed-off-by: Andrew Morton <5c1e68b099950c134891f0b6e179498a8ebe9cf9@linux-foundation.org>
Signed-off-by: Jens Axboe <cd8c6775e60d6f67a6984377324e5290df3d5358@kernel.dk>

KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas