[patch] scsi: use lock per host instead of per device for shared queue tag host

Ed Lin
2007-01-24T01:07:05Z

The block layer uses lock to protect request queue. Every scsi device
has a unique request queue, and queue lock is the default lock in struct
request_queue. This is good for normal cases. But for a host with
shared queue tag (e.g. stex controllers), a queue lock per device means
the shared queue tag is not protected when multiple devices are accessed
at a same time. This patch is a simple fix for this situation by introducing
a host queue lock to protect shared queue tag. Without this patch we will
see various kernel panics (including the BUG() and kernel errors in
blk_queue_start_tag and blk_queue_end_tag of ll_rw_blk.c) when accessing
different devices simultaneously (e.g. copying big file from one device to
another in smp kernels).

This is against kernel 2.6.20-rc5.

Signed-off-by: Ed Lin <ed.lin@promise.com>
---
drivers/scsi/scsi_lib.c | 2 +-
drivers/scsi/stex.c | 2 ++
include/scsi/scsi_host.h | 3 +++
3 files changed, 6 insertions(+), 1 deletion(-)

diff -purN a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
--- a/drivers/scsi/scsi_lib.c 2007-01-23 14:40:28.000000000 -0800
+++ b/drivers/scsi/scsi_lib.c 2007-01-23 14:46:43.000000000 -0800
@@ -1574,7 +1574,7 @@ struct request_queue *__scsi_alloc_queue
{
struct request_queue *q;

- q = blk_init_queue(request_fn, NULL);
+ q = blk_init_queue(request_fn, shost->req_q_lock);
if (!q)
return NULL;

diff -purN a/drivers/scsi/stex.c b/drivers/scsi/stex.c
--- a/drivers/scsi/stex.c 2007-01-23 14:40:28.000000000 -0800
+++ b/drivers/scsi/stex.c 2007-01-23 14:48:59.000000000 -0800
@@ -1254,6 +1254,8 @@ stex_probe(struct pci_dev *pdev, const s
if (err)
goto out_free_irq;

+ spin_lock_init(&host->__req_q_lock);
+ host->req_q_lock = &host->__req_q_lock;
err = scsi_init_shared_tag_map(host, host->can_queue);
if (err) {
printk(KERN_ERR DRV_NAME "(%s): init shared queue failed\n",
diff -purN a/include/scsi/scsi_host.h b/include/scsi/scsi_host.h
--- a/include/scsi/scsi_host.h 2007-01-23 14:40:29.000000000 -0800
+++ b/include/scsi/scsi_host.h 2007-01-23 14:57:04.000000000 -0800
@@ -508,6 +508,9 @@ struct Scsi_Host {
spinlock_t default_lock;
spinlock_t *host_lock;

+ spinlock_t __req_q_lock;
+ spinlock_t *req_q_lock;/* protect shared block queue tag */
+
struct mutex scan_mutex;/* serialize scanning activity */

struct list_head eh_cmd_q;