[PATCH v2 01/14] cxlflash: Set sg_tablesize to 1 instead of SG_NONE

[Uma Krishnan]

The following Oops is encountered when blk_mq is enabled with the
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 SCSI blk_mq stack assumes that sg_tablesize is always a non-zero
value with scsi_mq_setup_tags() allocating tags using sg_tablesize.
The cxlflash driver currently uses SG_NONE (0) for the sg_tablesize
as the devices it supports are not capable of scatter gather. This
mismatch of values results in the Oops above.

To resolve this issue, sg_tablesize for cxlflash can simply be set
to 1, a value which satisfies the constraints in cxlflash and the
lack of support of SG_NONE in SCSI blk_mq.

Signed-off-by: Uma Krishnan <ukrishn at linux.vnet.ibm.com>
Acked-by: Matthew R. Ochs <mrochs at linux.vnet.ibm.com>
---
 drivers/scsi/cxlflash/main.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/scsi/cxlflash/main.c b/drivers/scsi/cxlflash/main.c
index b301655..6004860 100644
--- a/drivers/scsi/cxlflash/main.c
+++ b/drivers/scsi/cxlflash/main.c
@@ -2377,7 +2377,7 @@ static struct scsi_host_template driver_template = {
 	.cmd_per_lun = CXLFLASH_MAX_CMDS_PER_LUN,
 	.can_queue = CXLFLASH_MAX_CMDS,
 	.this_id = -1,
-	.sg_tablesize = SG_NONE,	/* No scatter gather support */
+	.sg_tablesize = 1,	/* No scatter gather support */
 	.max_sectors = CXLFLASH_MAX_SECTORS,
 	.use_clustering = ENABLE_CLUSTERING,
 	.shost_attrs = cxlflash_host_attrs,
-- 
2.1.0