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; -- 2.1.0 -- 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
