linux-kernel - [PATCH] xhci: use iopoll for xhci

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Message-Id: <20190227221917.62567-1-djkurtz@chromium.org>
Date:   Wed, 27 Feb 2019 15:19:17 -0700
From:   Daniel Kurtz <djkurtz@...omium.org>
To:     unlisted-recipients:; (no To-header on input)
Cc:     rrangel@...omium.org, Daniel Kurtz <djkurtz@...omium.org>,
        Mathias Nyman <mathias.nyman@...el.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-usb@...r.kernel.org (open list:USB XHCI DRIVER),
        linux-kernel@...r.kernel.org (open list)
Subject: [PATCH] xhci: use iopoll for xhci_handshake

In cases such as xhci_abort_cmd_ring(), xhci_handshake() is called with
a spin lock held (and local interrupts disabled) with a huge 5 second
timeout.  This can translates to 5 million calls to udelay(1).  By its
very nature, udelay() is not meant to be precise, it only guarantees to
delay a minimum of 1 microsecond. Therefore the actual delay of
xhci_handshake() can be significantly longer.  If the average udelay(1)
is greater than 2.2 us, the total time in xhci_handshake() - with
interrupts disabled can be > 11 seconds triggering the kernel's soft lockup
detector.

To avoid this, let's replace the open coded io polling loop with one from
iopoll.h that uses a loop timed with the more presumably reliable ktime
infrastructure.

Signed-off-by: Daniel Kurtz <djkurtz@...omium.org>
---
 drivers/usb/host/xhci.c | 23 ++++++++++++-----------
 1 file changed, 12 insertions(+), 11 deletions(-)

diff --git a/drivers/usb/host/xhci.c b/drivers/usb/host/xhci.c
index 005e65922608e..fde5ff84ba69b 100644
--- a/drivers/usb/host/xhci.c
+++ b/drivers/usb/host/xhci.c
@@ -16,6 +16,7 @@
 #include <linux/slab.h>
 #include <linux/dmi.h>
 #include <linux/dma-mapping.h>
+#include <linux/iopoll.h>

 #include "xhci.h"
 #include "xhci-trace.h"
@@ -69,18 +70,18 @@ static bool td_on_ring(struct xhci_td *td, struct xhci_ring *ring)
 int xhci_handshake(void __iomem *ptr, u32 mask, u32 done, int usec)
 {
 	u32	result;
+	int ret;

-	do {
-		result = readl(ptr);
-		if (result == ~(u32)0)		/* card removed */
-			return -ENODEV;
-		result &= mask;
-		if (result == done)
-			return 0;
-		udelay(1);
-		usec--;
-	} while (usec > 0);
-	return -ETIMEDOUT;
+	ret = readl_poll_timeout_atomic(ptr, result,
+			((result & mask) == done || (result == ~(u32)0)),
+			1, usec);
+	if (ret)
+		return ret;
+
+	if (result == ~(u32)0)		/* card removed */
+		return -ENODEV;
+
+	return 0;
 }

 /*
-- 
2.21.0.rc2.261.ga7da99ff1b-goog