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From: "Andrea Parri (Microsoft)" <parri.andrea@gmail.com>
To: linux-kernel@vger.kernel.org, linux-hyperv@vger.kernel.org
Cc: "K . Y . Srinivasan" <kys@microsoft.com>,
	Haiyang Zhang <haiyangz@microsoft.com>,
	Stephen Hemminger <sthemmin@microsoft.com>,
	Wei Liu <wei.liu@kernel.org>, Dexuan Cui <decui@microsoft.com>,
	Michael Kelley <mikelley@microsoft.com>,
	Saruhan Karademir <skarade@microsoft.com>,
	Juan Vazquez <juvazq@microsoft.com>,
	"Andrea Parri (Microsoft)" <parri.andrea@gmail.com>,
	"James E.J. Bottomley" <jejb@linux.ibm.com>,
	"Martin K. Petersen" <martin.petersen@oracle.com>,
	linux-scsi@vger.kernel.org
Subject: [PATCH 1/3] scsi: storvsc: Fix max_outstanding_req_per_channel for Win8 and newer
Date: Thu, 17 Dec 2020 21:33:19 +0100	[thread overview]
Message-ID: <20201217203321.4539-2-parri.andrea@gmail.com> (raw)
In-Reply-To: <20201217203321.4539-1-parri.andrea@gmail.com>

Current code overestimates the value of max_outstanding_req_per_channel
for Win8 and newer hosts, since vmscsi_size_delta is set to the initial
value of sizeof(vmscsi_win8_extension) rather than zero.  This may lead
to wrong decisions when using ring_avail_percent_lowater equals to zero.
The estimate of max_outstanding_req_per_channel is 'exact' for Win7 and
older hosts.  A better choice, keeping the algorithm for the estimation
simple, is to err the other way around, i.e., to underestimate for Win7
and older but to use the exact value for Win8 and newer.

Suggested-by: Dexuan Cui <decui@microsoft.com>
Signed-off-by: Andrea Parri (Microsoft) <parri.andrea@gmail.com>
Cc: "James E.J. Bottomley" <jejb@linux.ibm.com>
Cc: "Martin K. Petersen" <martin.petersen@oracle.com>
Cc: linux-scsi@vger.kernel.org
---
 drivers/scsi/storvsc_drv.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/scsi/storvsc_drv.c b/drivers/scsi/storvsc_drv.c
index ded00a89bfc4e..64298aa2f151e 100644
--- a/drivers/scsi/storvsc_drv.c
+++ b/drivers/scsi/storvsc_drv.c
@@ -2141,12 +2141,15 @@ static int __init storvsc_drv_init(void)
 	 * than the ring buffer size since that page is reserved for
 	 * the ring buffer indices) by the max request size (which is
 	 * vmbus_channel_packet_multipage_buffer + struct vstor_packet + u64)
+	 *
+	 * The computation underestimates max_outstanding_req_per_channel
+	 * for Win7 and older hosts because it does not take into account
+	 * the vmscsi_size_delta correction to the max request size.
 	 */
 	max_outstanding_req_per_channel =
 		((storvsc_ringbuffer_size - PAGE_SIZE) /
 		ALIGN(MAX_MULTIPAGE_BUFFER_PACKET +
-		sizeof(struct vstor_packet) + sizeof(u64) -
-		vmscsi_size_delta,
+		sizeof(struct vstor_packet) + sizeof(u64),
 		sizeof(u64)));
 
 #if IS_ENABLED(CONFIG_SCSI_FC_ATTRS)
-- 
2.25.1


  reply	other threads:[~2020-12-17 20:35 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-12-17 20:33 [PATCH 0/3] scsi: storvsc: Validate length of incoming packet in storvsc_on_channel_callback() -- Take 2 Andrea Parri (Microsoft)
2020-12-17 20:33 ` Andrea Parri (Microsoft) [this message]
2020-12-17 21:31   ` [PATCH 1/3] scsi: storvsc: Fix max_outstanding_req_per_channel for Win8 and newer Dexuan Cui
2020-12-18 15:07   ` Michael Kelley
2020-12-17 20:33 ` [PATCH 2/3] scsi: storvsc: Resolve data race in storvsc_probe() Andrea Parri (Microsoft)
2020-12-17 21:31   ` Dexuan Cui
2020-12-18 15:14   ` Michael Kelley
2020-12-17 20:33 ` [PATCH 3/3] scsi: storvsc: Validate length of incoming packet in storvsc_on_channel_callback() Andrea Parri (Microsoft)
2020-12-17 21:31   ` Dexuan Cui
2020-12-18 15:16   ` Michael Kelley
2021-03-29 16:37   ` Olaf Hering
2021-03-30  9:08     ` Andrea Parri
2021-01-08  4:15 ` [PATCH 0/3] scsi: storvsc: Validate length of incoming packet in storvsc_on_channel_callback() -- Take 2 Martin K. Petersen
2021-01-13  5:48 ` Martin K. Petersen

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