linux-kernel - [34-longterm 135/247] xhci: Fix errors in the running total calculations in the TRB math

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Message-Id: <1308850515-15242-76-git-send-email-paul.gortmaker@windriver.com>
Date:	Thu, 23 Jun 2011 13:33:23 -0400
From:	Paul Gortmaker <paul.gortmaker@...driver.com>
To:	stable@...nel.org, linux-kernel@...r.kernel.org
Cc:	stable-review@...nel.org,
	Paul Zimmerman <Paul.Zimmerman@...opsys.com>,
	Paul Zimmerman <paulz@...opsys.com>,
	Sarah Sharp <sarah.a.sharp@...ux.intel.com>,
	Paul Gortmaker <paul.gortmaker@...driver.com>
Subject: [34-longterm 135/247] xhci: Fix errors in the running total calculations in the TRB math

From: Paul Zimmerman <Paul.Zimmerman@...opsys.com>

                   -------------------
    This is a commit scheduled for the next v2.6.34 longterm release.
    If you see a problem with using this for longterm, please comment.
                   -------------------

commit 5807795bd4dececdf553719cc02869e633395787 upstream.

Calculations like

	running_total = TRB_MAX_BUFF_SIZE -
		(sg_dma_address(sg) & (TRB_MAX_BUFF_SIZE - 1));
	if (running_total != 0)
		num_trbs++;

are incorrect, because running_total can never be zero, so the if()
expression will never be true. I think the intention was that
running_total be in the range of 0 to TRB_MAX_BUFF_SIZE-1, not 1
to TRB_MAX_BUFF_SIZE. So adding a

	running_total &= TRB_MAX_BUFF_SIZE - 1;

fixes the problem.

This patch should be queued for stable kernels back to 2.6.31.

[PG: 34 doesn't have count_isoc_trbs_needed() hence this has
only two of the three upstream running_total changes.]

Signed-off-by: Paul Zimmerman <paulz@...opsys.com>
Signed-off-by: Sarah Sharp <sarah.a.sharp@...ux.intel.com>
Signed-off-by: Paul Gortmaker <paul.gortmaker@...driver.com>
---
 drivers/usb/host/xhci-ring.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/drivers/usb/host/xhci-ring.c b/drivers/usb/host/xhci-ring.c
index 8bf5563..e4afa99 100644
--- a/drivers/usb/host/xhci-ring.c
+++ b/drivers/usb/host/xhci-ring.c
@@ -1711,6 +1711,7 @@ static unsigned int count_sg_trbs_needed(struct xhci_hcd *xhci, struct urb *urb)
 		/* Scatter gather list entries may cross 64KB boundaries */
 		running_total = TRB_MAX_BUFF_SIZE -
 			(sg_dma_address(sg) & (TRB_MAX_BUFF_SIZE - 1));
+		running_total &= TRB_MAX_BUFF_SIZE - 1;
 		if (running_total != 0)
 			num_trbs++;
 
@@ -1978,6 +1979,7 @@ int xhci_queue_bulk_tx(struct xhci_hcd *xhci, gfp_t mem_flags,
 	/* How much data is (potentially) left before the 64KB boundary? */
 	running_total = TRB_MAX_BUFF_SIZE -
 		(urb->transfer_dma & (TRB_MAX_BUFF_SIZE - 1));
+	running_total &= TRB_MAX_BUFF_SIZE - 1;
 
 	/* If there's some data on this 64KB chunk, or we have to send a
 	 * zero-length transfer, we need at least one TRB
-- 
1.7.4.4

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