Commit 53674ac5 authored by Jens Axboe's avatar Jens Axboe
Browse files

block: add warning to blk_make_request() 



Add a note about how one needs to be careful when setting up these bio
chains.

Extracted from Boaz's updated patch.

Signed-off-by: default avatarJens Axboe <jens.axboe@oracle.com>
parent a411f4bb

block/blk-core.c

+9 −0
Original line number Diff line number Diff line
@@ -910,6 +910,15 @@ EXPORT_SYMBOL(blk_get_request); 
 * need bouncing, by calling the appropriate masked or flagged allocator,

 * suitable for the target device. Otherwise the call to blk_queue_bounce will

 * BUG.

 *

 * WARNING: When allocating/cloning a bio-chain, careful consideration should be

 * given to how you allocate bios. In particular, you cannot use __GFP_WAIT for

 * anything but the first bio in the chain. Otherwise you risk waiting for IO

 * completion of a bio that hasn't been submitted yet, thus resulting in a

 * deadlock. Alternatively bios should be allocated using bio_kmalloc() instead

 * of bio_alloc(), as that avoids the mempool deadlock.

 * If possible a big IO should be split into smaller parts when allocation

 * fails. Partial allocation should not be an error, or you risk a live-lock.

 */

struct request *blk_make_request(struct request_queue *q, struct bio *bio,

				 gfp_t gfp_mask)