linux-kernel - [PATCH] scsi: hisi_sas: Fix memory ordering in hisi_sas_task

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Date:   Tue, 17 May 2022 16:04:21 +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>,
        <linuxarm@...wei.com>, John Garry <john.garry@...wei.com>
Subject: [PATCH] scsi: hisi_sas: Fix memory ordering in hisi_sas_task_deliver()

The memories for the slot should be observed to be written prior to
observing the slot as ready.

Prior to commit 26fc0ea74fcb ("scsi: libsas: Drop SAS_TASK_AT_INITIATOR"),
we had a spin_lock() + spin_unlock() immediately before marking the slot
as ready. The spin_unlock() - with release semantics - caused the slot
memory to be observed to be written.

Now that the spin_lock() + spin_unlock() is gone, use a smp_wmb().

Fixes: 26fc0ea74fcb ("scsi: libsas: Drop SAS_TASK_AT_INITIATOR")
Reported-by: Yihang Li <liyihang6@...ilicon.com>
Tested-by: Yihang Li <liyihang6@...ilicon.com>
Signed-off-by: John Garry <john.garry@...wei.com>
---
Hi Martin, Please consider for v5.18, thanks!

diff --git a/drivers/scsi/hisi_sas/hisi_sas_main.c b/drivers/scsi/hisi_sas/hisi_sas_main.c
index 4bda2f6cb352..f56dd01230ce 100644
--- a/drivers/scsi/hisi_sas/hisi_sas_main.c
+++ b/drivers/scsi/hisi_sas/hisi_sas_main.c
@@ -446,6 +446,8 @@ void hisi_sas_task_deliver(struct hisi_hba *hisi_hba,
 		return;
 	}
 
+	/* Make slot memories observable before marking as ready */
+	smp_wmb();
 	WRITE_ONCE(slot->ready, 1);
 
 	spin_lock(&dq->lock);
-- 
2.26.2