On Thursday 02 October 2008 19:59:33 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. > > 8,0 0 12 1.943680621 2261 Q R 6184075 + 55 [bash] > 8,0 0 13 1.943684671 2261 G R 6184075 + 55 [bash] > 8,0 0 14 1.943690189 2261 P N [bash] > 8,0 0 15 1.943692075 2261 I R 6184075 + 55 [bash] > 8,0 0 16 1.943712119 2261 D R 6184075 + 55 [bash] > 8,0 0 17 1.943718684 2261 Q R 6184130 + 55 [bash] > 8,0 0 18 1.943721897 2261 G R 6184130 + 55 [bash] > 8,0 0 19 1.943726576 2261 P N [bash] > 8,0 0 20 1.943727763 2261 I R 6184130 + 55 [bash] > 8,0 0 21 1.943731675 2261 Q R 6184241 + 56 [bash] > 8,0 0 22 1.943735167 2261 G R 6184241 + 56 [bash] > 8,0 0 23 1.943739497 2261 I R 6184241 + 56 [bash] > 8,0 0 24 1.943742081 2261 Q R 6184185 + 56 [bash] > 8,0 0 25 1.943744875 2261 M R 6184185 + 56 [bash] > 8,0 0 26 1.943753535 2261 Q R 6184352 + 55 [bash] > 8,0 0 27 1.943756538 2261 G R 6184352 + 55 [bash] > 8,0 0 28 1.943760868 2261 I R 6184352 + 55 [bash] > 8,0 0 29 1.943763522 2261 Q R 6184407 + 55 [bash] > 8,0 0 30 1.943766316 2261 M R 6184407 + 55 [bash] > 8,0 0 31 1.943770506 2261 Q R 6184297 + 55 [bash] > 8,0 0 32 1.943772951 2261 F R 6184297 + 55 [bash] > 8,0 0 33 1.943780843 2261 Q R 6184462 + 55 [bash] > 8,0 0 34 1.943783776 2261 M R 6184462 + 55 [bash] > 8,0 0 35 1.944444684 0 UT N [swapper] 2 > 8,0 0 36 1.944453624 10 U N [kblockd/0] 2 > 8,0 0 37 1.944470595 10 D R 6184130 + 387 [kblockd/0] > 8,0 0 38 1.970340853 0 C R 6184075 + 55 [0] > 8,0 0 39 1.973576739 0 C R 6184130 + 387 [0] > > Oops, that was incomplete information to reproduce the issue. typedef struct { int IoSize; char *Mem; } DB_MEM_LIST, *pDB_MEM_LIST; DB_MEM_LIST dbMemList[NUM_BIO] = { { 0x6e00, NULL }, { 0x6e00, NULL }, { 0x7000, NULL }, { 0x7000, NULL }, { 0x6e00, NULL }, { 0x6e00, NULL }, { 0x6e00, NULL }, { 0x6e00, NULL }, }; // Allocate Memory. char *Mem0 = kmalloc(dbMemList[0].IoSize, GFP_KERNEL); char *Mem1 = kmalloc(dbMemList[1].IoSize, GFP_KERNEL); char *Mem2 = kmalloc((dbMemList[2].IoSize + dbMemList[3].IoSize + dbMemList[4].IoSize), GFP_KERNEL); char *Mem5 = kmalloc(dbMemList[5].IoSize, GFP_KERNEL); char *Mem6 = kmalloc(dbMemList[6].IoSize, GFP_KERNEL); char *Mem7 = kmalloc(dbMemList[7].IoSize, GFP_KERNEL); dbMemList[0].Mem = Mem0; dbMemList[1].Mem = Mem1; dbMemList[2].Mem = Mem2; dbMemList[3].Mem = dbMemList[2].Mem + dbMemList[2].IoSize; dbMemList[4].Mem = dbMemList[3].Mem + dbMemList[3].IoSize; dbMemList[5].Mem = Mem5; dbMemList[6].Mem = Mem6; dbMemList[7].Mem = Mem7; int Loop; struct bio *BioList[NUM_BIO] = { NULL }; struct bio *Bio = NULL; long Sector; /* ** Allocate BIOs. */ for(Loop = 0; Loop < NUM_BIO; Loop++) BioList[Loop] = bio_alloc(GFP_KERNEL, NUMBER_OF_VECS); for(Loop = 0; Loop < NUM_BIO; Loop++) { Bio = BioList[Loop]; Bio->bi_sector = Sector; Bio->bi_bdev = Bdev; Bio->bi_end_io = db_end_io; if (Loop == 0) { if (!bio_add_page(BioList[Loop], virt_to_page(dbMemList[Loop].Mem), 0x3000, offset_in_page(dbMemList[Loop].Mem))) { printk("NIK: bio add page failed- %dA\n", Loop); } if (!bio_add_page(BioList[Loop], virt_to_page(dbMemList[7].Mem), 0x3e00, offset_in_page(dbMemList[7].Mem))) { printk("NIK: bio add page failed- %dB\n", Loop); } } else if (Loop == 7) { if (!bio_add_page(BioList[Loop], virt_to_page(dbMemList[Loop].Mem), 0x2000, offset_in_page(dbMemList[Loop].Mem))) { printk("NIK: bio add page failed- %dA\n", Loop); } if (!bio_add_page(BioList[Loop], virt_to_page(dbMemList[7].Mem), 0x4e00, offset_in_page(dbMemList[7].Mem))) { printk("NIK: bio add page failed- %dB\n", Loop); } } else if (!bio_add_page(BioList[Loop], virt_to_page(dbMemList[Loop].Mem), dbMemList[Loop].IoSize, offset_in_page(dbMemList[Loop].Mem))) { printk("NIK: bio add page failed %d\n", Loop); } Sector += (Bio->bi_size / 512); } submit_bio(READ, BioList[0]); // 1 submit_bio(READ, BioList[1]); // 2 submit_bio(READ, BioList[3]); // 4 submit_bio(READ, BioList[2]); // 3 submit_bio(READ, BioList[5]); // 6 submit_bio(READ, BioList[6]); // 7 submit_bio(READ, BioList[4]); // 5 submit_bio(READ, BioList[7]); // 8 Thanks Nikanth Karthikesan -- 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
