linux-kernel - [ 38/41] i2c-algo-bit: Fix spurious SCL timeouts under heavy load

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Date:	Fri, 16 Mar 2012 16:38:48 -0700
From:	Greg KH <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	alan@...rguk.ukuu.org.uk, Ville Syrjala <syrjala@....fi>,
	Jean Delvare <khali@...ux-fr.org>
Subject: [ 38/41] i2c-algo-bit: Fix spurious SCL timeouts under heavy load

3.2-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Ville Syrjala <syrjala@....fi>

commit 8ee161ce5e0cfc689eb677f227a6248191165fac upstream.

When the system is under heavy load, there can be a significant delay
between the getscl() and time_after() calls inside sclhi(). That delay
may cause the time_after() check to trigger after SCL has gone high,
causing sclhi() to return -ETIMEDOUT.

To fix the problem, double check that SCL is still low after the
timeout has been reached, before deciding to return -ETIMEDOUT.

Signed-off-by: Ville Syrjala <syrjala@....fi>
Signed-off-by: Jean Delvare <khali@...ux-fr.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/i2c/algos/i2c-algo-bit.c |    8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

--- a/drivers/i2c/algos/i2c-algo-bit.c
+++ b/drivers/i2c/algos/i2c-algo-bit.c
@@ -103,8 +103,14 @@ static int sclhi(struct i2c_algo_bit_dat
 		 * chips may hold it low ("clock stretching") while they
 		 * are processing data internally.
 		 */
-		if (time_after(jiffies, start + adap->timeout))
+		if (time_after(jiffies, start + adap->timeout)) {
+			/* Test one last time, as we may have been preempted
+			 * between last check and timeout test.
+			 */
+			if (getscl(adap))
+				break;
 			return -ETIMEDOUT;
+		}
 		cond_resched();
 	}
 #ifdef DEBUG


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