linux-kernel - [PATCH] scsi: core: Cap initial sdev queue depth at shost.can

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Date:   Tue, 20 Apr 2021 00:06:24 +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>,
        <kashyap.desai@...adcom.com>, <ming.lei@...hat.com>,
        <dgilbert@...erlog.com>, John Garry <john.garry@...wei.com>
Subject: [PATCH] scsi: core: Cap initial sdev queue depth at shost.can_queue

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

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

Stop this happened by capping initial sdev queue depth at can_queue.

Signed-off-by: John Garry <john.garry@...wei.com>
---
Topic originally discussed at:
https://lore.kernel.org/linux-scsi/85dec8eb-8eab-c7d6-b0fb-5622747c5499@interlog.com/T/#m5663d0cac657d843b93d0c9a2374f98fc04384b9

Last idea there was to error/warn in scsi_add_host() for cmd_per_lun >
can_queue. However, such a shost driver could still configure the sdev
queue depth to be sound value at .slave_configure callback, so now thinking
the orig patch better.

diff --git a/drivers/scsi/scsi_scan.c b/drivers/scsi/scsi_scan.c
index 9f1b7f3c650a..8de2f830bcdc 100644
--- a/drivers/scsi/scsi_scan.c
+++ b/drivers/scsi/scsi_scan.c
@@ -277,7 +277,11 @@ static struct scsi_device *scsi_alloc_sdev(struct scsi_target *starget,
 	WARN_ON_ONCE(!blk_get_queue(sdev->request_queue));
 	sdev->request_queue->queuedata = sdev;
 
-	depth = sdev->host->cmd_per_lun ?: 1;
+	if (sdev->host->cmd_per_lun)
+		depth = min_t(unsigned int, sdev->host->cmd_per_lun,
+			      sdev->host->can_queue);
+	else
+		depth = 1;
 
 	/*
 	 * Use .can_queue as budget map's depth because we have to
-- 
2.26.2