On 05/19/2009 01:13 PM, Jens Axboe wrote: > On Tue, May 19 2009, Boaz Harrosh wrote: <snip> >> Thanks Jens, for your comment. >> >> I have three sources of bio allocations. >> 1. bio_map_kern which uses bio_kmalloc (recently fixed by Tejun) >> 2. by osdblk which does a clone and will not ever wait. >> (I've fixed the code to split up the IO on allocation failure into >> smaller requests (will repost soon)) >> 3. Future code in exofs and pNFS-Client that will only ever use bio_kmalloc. > > All of those are fine! > >> Should we add something to the Documentation, and/or above doc_book comment >> to warn off users? > > Yes I think so. I'm generally weary of adding interfaces that are easy > to misuse. This one has that potential, but it also has merits. So I'll > merge your series, if you could send a patch updating the > comment/docbook, then that would be great. > As my English sucks, please read proof below addition. I will repost later today. Should I just post this one patch, or all the 5? (alternatively I have these on a public git tree reabased on block/for-next branch.) Thanks Boaz --- diff --git a/block/blk-core.c b/block/blk-core.c index 89261d2..4dc4e32 100644 --- a/block/blk-core.c +++ b/block/blk-core.c @@ -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 deadlocking, + * waiting for a bio to be returned to the pool, which will never return, since + * it was not submitted yet. + * Alternatively bios should be allocated using bio_kmalloc only. + * If possible a long 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) -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
