linux-kernel - [PATCH 1/9] scsi: scsi_debug: Don't iter all hosts in clear_luns_changed_on

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Message-Id: <20230313111019.1521680-2-john.g.garry@oracle.com>
Date:   Mon, 13 Mar 2023 11:10:11 +0000
From:   John Garry <john.g.garry@...cle.com>
To:     jejb@...ux.ibm.com, martin.petersen@...cle.com, hch@....de,
        dgilbert@...erlog.com, hare@...e.com, ming.lei@...hat.com,
        bvanassche@....org
Cc:     linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org,
        John Garry <john.g.garry@...cle.com>
Subject: [PATCH 1/9] scsi: scsi_debug: Don't iter all hosts in clear_luns_changed_on_target()

In clear_luns_changed_on_target(), we iter all devices for all hosts to
conditionally clear the SDEBUG_UA_LUNS_CHANGED flag in the per-device
uas_bm.

One condition to see whether we clear the flag is to test whether the host
for the device under consideration is the same as the matching device's
(devip) host. This check will only ever pass for devices for the same host,
so only iter the devices for the matching device host.

We can now drop the spinlock'ing of the sdebug_host_list_lock in the same
function. This will allow us to use a mutex instead of the spinlock for
the global host lock, as clear_luns_changed_on_target() could be called
in non-blocking context, in scsi_debug_queuecommand() -> make_ua() ->
clear_luns_changed_on_target() (which is why required a spinlock).

Signed-off-by: John Garry <john.g.garry@...cle.com>
---
 drivers/scsi/scsi_debug.c | 13 +++++--------
 1 file changed, 5 insertions(+), 8 deletions(-)

diff --git a/drivers/scsi/scsi_debug.c b/drivers/scsi/scsi_debug.c
index 52e33ecc6122..6e6eca694bb5 100644
--- a/drivers/scsi/scsi_debug.c
+++ b/drivers/scsi/scsi_debug.c
@@ -1063,18 +1063,15 @@ static void all_config_cdb_len(void)

 static void clear_luns_changed_on_target(struct sdebug_dev_info *devip)
 {
-	struct sdebug_host_info *sdhp;
+	struct sdebug_host_info *sdhp = devip->sdbg_host;
 	struct sdebug_dev_info *dp;

-	spin_lock(&sdebug_host_list_lock);
-	list_for_each_entry(sdhp, &sdebug_host_list, host_list) {
-		list_for_each_entry(dp, &sdhp->dev_info_list, dev_list) {
-			if ((devip->sdbg_host == dp->sdbg_host) &&
-			    (devip->target == dp->target))
-				clear_bit(SDEBUG_UA_LUNS_CHANGED, dp->uas_bm);
+	list_for_each_entry(dp, &sdhp->dev_info_list, dev_list) {
+		if ((devip->sdbg_host == dp->sdbg_host) &&
+		    (devip->target == dp->target)) {
+			clear_bit(SDEBUG_UA_LUNS_CHANGED, dp->uas_bm);
 		}
 	}
-	spin_unlock(&sdebug_host_list_lock);
 }

 static int make_ua(struct scsi_cmnd *scp, struct sdebug_dev_info *devip)
-- 
2.35.3