The patch below does not apply to the 4.16-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 6de3b1f26d1e8adb53d97835400c541ce50155e5 Mon Sep 17 00:00:00 2001

From: Mika Kuoppala mika.kuoppala@linux.intel.com Date: Mon, 23 Apr 2018 14:37:53 +0300 Subject: [PATCH] drm/i915: Use ktime on wait_for MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit

We use jiffies to determine when wait expires. However Imre did find out that jiffies can and will do a >1 increments on certain situations [1]. When this happens in a wait_for loop, we return timeout errorneously much earlier than what the real wallclock would say.

We can't afford our waits to timeout prematurely. Discard jiffies and change to ktime to detect timeouts.

v2: added bugzilla entry (Imre), added stable (Chris)

Reported-by: Imre Deak imre.deak@intel.com References: https://lkml.org/lkml/2018/4/18/798 [1] Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=105771 Cc: Imre Deak imre.deak@intel.com Cc: Chris Wilson chris@chris-wilson.co.uk Cc: Ville Syrjälä ville.syrjala@linux.intel.com Cc: stable@vger.kernel.org Signed-off-by: Mika Kuoppala mika.kuoppala@linux.intel.com Reviewed-by: Chris Wilson chris@chris-wilson.co.uk Link: https://patchwork.freedesktop.org/patch/msgid/20180423113754.28424-1-mika.ku... (cherry picked from commit 3085982c6b45d7d22f76e3aa018affbc143a7370) Signed-off-by: Joonas Lahtinen joonas.lahtinen@linux.intel.com

diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h index d4368589b355..a80fbad9be0f 100644 --- a/drivers/gpu/drm/i915/intel_drv.h +++ b/drivers/gpu/drm/i915/intel_drv.h @@ -49,12 +49,12 @@ * check the condition before the timeout. */ #define __wait_for(OP, COND, US, Wmin, Wmax) ({ \ - unsigned long timeout__ = jiffies + usecs_to_jiffies(US) + 1; \ + const ktime_t end__ = ktime_add_ns(ktime_get_raw(), 1000ll * (US)); \ long wait__ = (Wmin); /* recommended min for usleep is 10 us */ \ int ret__; \ might_sleep(); \ for (;;) { \ - bool expired__ = time_after(jiffies, timeout__); \ + const bool expired__ = ktime_after(ktime_get_raw(), end__); \ OP; \ if (COND) { \ ret__ = 0; \