From ab548fd21e1cbe601ce5f775254a6d042c6495f2 Mon Sep 17 00:00:00 2001 From: "Andrea Parri (Microsoft)" Date: Thu, 17 Dec 2020 21:33:19 +0100 Subject: [PATCH] scsi: storvsc: Fix max_outstanding_req_per_channel for Win8 and newer 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. Link: https://lore.kernel.org/r/20201217203321.4539-2-parri.andrea@gmail.com Cc: "James E.J. Bottomley" Cc: "Martin K. Petersen" Cc: linux-scsi@vger.kernel.org Suggested-by: Dexuan Cui Reviewed-by: Dexuan Cui Reviewed-by: Michael Kelley Signed-off-by: Andrea Parri (Microsoft) Signed-off-by: Martin K. Petersen --- 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 2e4fa77445fd..2d9dd30cc921 100644 --- a/drivers/scsi/storvsc_drv.c +++ b/drivers/scsi/storvsc_drv.c @@ -2161,12 +2161,15 @@ 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)