On Thu, 2008-10-02 at 19:59 +0530, Nikanth Karthikesan wrote: > This is a follow-up to my earlier mail http://lkml.org/lkml/2008/9/23/294 > ([PATCH] BUG: ll_merge_requests_fn() updates req->nr_phys_segments wrongly) > > It is possible for the merging code to create lesser no of phys segments than > hw segments, but every hw segment needs atleast one new phys segment. This > triggers the BUG() on scsi_init_sgtable() as blk_rq_map_sg() returns more no > of segments than rq->nr_phys_segments > > The following blktrace shows a sequence of bio's to trigger such condition on > my machine with max_sectors_kb=512 & max_hw_sectors_kb=32767. Um, don't you mean this the other way around? I can see this problem occurring if the block layer gets tricked into doing a physical merge where sector limits forbid a virtual merge. The bug would appear to be that we sometimes only look at q->max_sectors when deciding on mergability. Either we have to insist on max_sectors <= hw_max_sectors, or we have to start using min(q->max_sectors, q->max_hw_sectors) for this. James -- 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
