[PATCH] NVMe: Prevent bogus synchronous IO command timeouts.

[Jeffrey Lien]

Keith,
This looks like a much simpler fix with less impact on performance.   I'll do some testing of it to verify it indeed resolves the problem we were seeing.  I'll let you know how it goes in a day or 2.   Thanks.  

-----Original Message-----
From: Keith Busch [mailto:keith.busch at intel.com] 
Sent: Tuesday, September 29, 2015 3:03 PM
To: Jeffrey Lien <Jeff.Lien at hgst.com>
Cc: Busch, Keith <keith.busch at intel.com>; linux-nvme at lists.infradead.org
Subject: Re: [PATCH] NVMe: Prevent bogus synchronous IO command timeouts.

On Tue, 29 Sep 2015, Jeffrey Lien wrote:
> Attached the patch since I can't get it sent via send-email.

If possible, you will want to remove the confidentiality disclaimer from emails to public lists.

On your patch, I think it will be very bad for performance. We can achieve the protection you're going for without spinlocks and use memory barriers instead. What do you think for the following?

---
diff --git a/drivers/block/nvme-core.c b/drivers/block/nvme-core.c index 78e51c2..2d21827 100644
--- a/drivers/block/nvme-core.c
+++ b/drivers/block/nvme-core.c
@@ -200,9 +200,10 @@ static int alloc_cmdid(struct nvme_queue *nvmeq, void *ctx,
  	} while (test_and_set_bit(cmdid, nvmeq->cmdid_data));

  	info[cmdid].fn = handler;
-	info[cmdid].ctx = ctx;
  	info[cmdid].timeout = jiffies + timeout;
  	info[cmdid].aborted = 0;
+	wmb();
+	info[cmdid].ctx = ctx;
  	return cmdid;
  }

@@ -1354,9 +1355,9 @@ static void nvme_cancel_ios(struct nvme_queue *nvmeq, bool timeout)
  			.status = cpu_to_le16(NVME_SC_ABORT_REQ << 1),
  		};

-		if (timeout && !time_after(now, info[cmdid].timeout))
+		if (info[cmdid].ctx == CMD_CTX_CANCELLED || info[cmdid].ctx == 
+CMD_CTX_COMPLETED)
  			continue;
-		if (info[cmdid].ctx == CMD_CTX_CANCELLED)
+		if (timeout && !time_after(now, info[cmdid].timeout))
  			continue;
  		if (timeout && info[cmdid].ctx == CMD_CTX_ASYNC)
  			continue;
--
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