Messages in this thread | | | Subject | Re: [PATCH] BUG: nr_phys_segments cannot be less than nr_hw_segments | From | James Bottomley <> | Date | Thu, 02 Oct 2008 10:03:33 -0500 |
| |
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
| |