On Tue, 23 Sep 2008 23:58:02 +0530 Nikanth Karthikesan <knikanth@xxxxxxx> wrote: > > From: Nikanth Karthikesan <knikanth@xxxxxxx> > > ll_merge_requests_fn() decreases the req->nr_phys_segments if > blk_phys_contig_segment() returns true, but it is perfectly possible that > blk_hw_contig_segment() is false. Yeah, in fact, blk_hw_contig_segment() is always false on the majority of architectures (on only PARISC and Alpha, it could be true). Your patch doesn't look correct. Virtually, the patch always disables physical merging. > A new hw_segment implies a new phys_segment. > So decrementing nr_phys_segments wrongly here triggers the BUG_ON() in > scsi_init_sgtable(), as blk_rq_map_sg() would map 1 phys_segment more than > req->nr_phys_segment. This is easily reproducible. Other callers of > blk_rq_map_sg() should also be affected by this bug. I have no idea how BUG_ON() in scsi_init_sgtable() is triggered. Can you give more information, HBA, IOMMU (if you use), and the values of req->nr_phys_segment, req->nr_hw_segment, count, etc in in scsi_init_sgtable() when you hit the bug? BTW, blk_hw_contig_segment() will be removed for 2.6.28 (virtual merging account in the block layer will be removed). -- 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
