On 11/10/2015 11:45 PM, Manoj Kumar wrote: > Oops while testing blk_mq over the new cxlflash driver. > > [ 2960.817172] Oops: Kernel access of bad area, sig: 11 [#5] > [ 2960.817309] NIP __blk_mq_run_hw_queue+0x278/0x4c0 > [ 2960.817313] LR __blk_mq_run_hw_queue+0x2bc/0x4c0 > [ 2960.817314] Call Trace: > [ 2960.817320] __blk_mq_run_hw_queue+0x2bc/0x4c0 (unreliable) > [ 2960.817324] blk_mq_run_hw_queue+0xd8/0x100 > [ 2960.817329] blk_mq_insert_requests+0x14c/0x1f0 > [ 2960.817333] blk_mq_flush_plug_list+0x150/0x190 > [ 2960.817338] blk_flush_plug_list+0x11c/0x2b0 > [ 2960.817344] blk_finish_plug+0x58/0x80 > [ 2960.817348] __do_page_cache_readahead+0x1c0/0x2e0 > [ 2960.817352] force_page_cache_readahead+0x68/0xd0 > [ 2960.817356] generic_file_read_iter+0x43c/0x6a0 > [ 2960.817359] blkdev_read_iter+0x68/0xa0 > [ 2960.817361] __vfs_read+0x11c/0x180 > [ 2960.817364] vfs_read+0xa4/0x1c0 > [ 2960.817366] SyS_read+0x6c/0x110 > [ 2960.817369] system_call+0x38/0xb4 > > The root cause of the problem was this low level device driver(LLDD), > in this case cxlflash, does not support scatter-gather and hence had > set it's sg_tablesize to SG_NONE (value of 0). In reality the tablesize > is of length 1. This value of SG_NONE does not cause any problems with > the standard block driver stack but causes issues for blk_mq, as shown > above. Since quite a few of the legacy LLDDs are setting sg_tablesize > to SG_NONE, it was preferable to override the LLDD provided value in > scsi_host_alloc(). > > Signed-off-by: Manoj N. Kumar <manoj@xxxxxxxxxxxxxxxxxx> > Signed-off-by: Youngjae Lee <leeyo@xxxxxxxxxxxxxxxxxx> > Reviewed-by: Matthew R. Ochs <mrochs@xxxxxxxxxxxxxxxxxx> > --- > drivers/scsi/hosts.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/scsi/hosts.c b/drivers/scsi/hosts.c > index 8bb173e..bd13c9d 100644 > --- a/drivers/scsi/hosts.c > +++ b/drivers/scsi/hosts.c > @@ -413,7 +413,7 @@ struct Scsi_Host *scsi_host_alloc(struct scsi_host_template *sht, int privsize) > shost->hostt = sht; > shost->this_id = sht->this_id; > shost->can_queue = sht->can_queue; > - shost->sg_tablesize = sht->sg_tablesize; > + shost->sg_tablesize = (sht->sg_tablesize ? sht->sg_tablesize : 1); > shost->sg_prot_tablesize = sht->sg_prot_tablesize; > shost->cmd_per_lun = sht->cmd_per_lun; > shost->unchecked_isa_dma = sht->unchecked_isa_dma; > Shouldn't we rather fixup blk-mq to properly support SG_NONE? Silently converting SG_NONE (=0) to 1 has a fair chance of breaking non-mq enabled setups, which happily work with SG_NONE currently. Cheers, Hannes -- Dr. Hannes Reinecke zSeries & Storage hare@xxxxxxx +49 911 74053 688 SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg GF: F. Imendörffer, J. Smithard, J. Guild, D. Upmanyu, G. Norton HRB 21284 (AG Nürnberg) -- 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
