linux-kernel - [PATCH] scsi: core: Cap shost cmd_per_lun at can

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Date:   Wed, 19 May 2021 22:31:02 +0800
From:   John Garry <john.garry@...wei.com>
To:     <jejb@...ux.ibm.com>, <martin.petersen@...cle.com>
CC:     <linux-scsi@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <ming.lei@...hat.com>, John Garry <john.garry@...wei.com>
Subject: [PATCH] scsi: core: Cap shost cmd_per_lun at can_queue

Function sdev_store_queue_depth() enforces that the sdev queue depth cannot
exceed Shost.can_queue.

The sdev initial value comes from shost cmd_per_lun.

However, the LLDD may still set cmd_per_lun > can_queue, which leads to an
initial sdev queue depth greater than can_queue.

Such an issue was reported in [0], which caused a hang. That has since
been fixed in commit fc09acb7de31 ("scsi: scsi_debug: Fix cmd_per_lun,
set to max_queue").

Stop this possibly happening for other drivers by capping
shost.cmd_per_lun at shost.can_queue.

[0] https://lore.kernel.org/linux-scsi/YHaez6iN2HHYxYOh@T590/

Signed-off-by: John Garry <john.garry@...wei.com>
---
Earlier patch was in https://lore.kernel.org/linux-scsi/1618848384-204144-1-git-send-email-john.garry@huawei.com/

diff --git a/drivers/scsi/hosts.c b/drivers/scsi/hosts.c
index ba72bd4202a2..624e2582c3df 100644
--- a/drivers/scsi/hosts.c
+++ b/drivers/scsi/hosts.c
@@ -220,6 +220,9 @@ int scsi_add_host_with_dma(struct Scsi_Host *shost, struct device *dev,
 		goto fail;
 	}

+	shost->cmd_per_lun = min_t(short, shost->cmd_per_lun,
+				   shost->can_queue);
+
 	error = scsi_init_sense_cache(shost);
 	if (error)
 		goto fail;
-- 
2.26.2