On Thu, Mar 28, 2013 at 12:03:25AM +0100, Daniel Vetter wrote: > As Thomas Gleixner spotted, it's rather horrible racy: > - We can miss almost a full tick, so need to compensate by 1 jiffy.
I have a feeling this is a rather common pattern, so I wonder if [mu]secs_to_jiffies() should do the +1 already for everyone. Or maybe there should be some other macros for specifying timeouts that would do the +1. > - We need to re-check the condition when having timed-out, since a > the last check could have been before the timeout expired. E.g. when > we've been preempted or a long irq happened. > > Cc: Thomas Gleixner <[email protected]> > Reported-by: Jack Winter <[email protected]> > Cc: Jack Winter <[email protected]> > Signed-off-by: Daniel Vetter <[email protected]> Reviewed-by: Ville Syrjälä <[email protected]> > --- > drivers/gpu/drm/i915/intel_drv.h | 13 +++++++++++-- > 1 file changed, 11 insertions(+), 2 deletions(-) > > diff --git a/drivers/gpu/drm/i915/intel_drv.h > b/drivers/gpu/drm/i915/intel_drv.h > index c8c1979..9dcae4e 100644 > --- a/drivers/gpu/drm/i915/intel_drv.h > +++ b/drivers/gpu/drm/i915/intel_drv.h > @@ -33,12 +33,21 @@ > #include <drm/drm_fb_helper.h> > #include <drm/drm_dp_helper.h> > > +/** > + * _wait_for - magic (register) wait macro > + * > + * Does the right thing for modeset paths when run under kdgb or similar > atomic > + * contexts. Note that it's important that we check the condition again after > + * having timed out, since the timeout could be due to preemption or similar > and > + * we've never had a chance to check the condition before the timeout. > + */ > #define _wait_for(COND, MS, W) ({ \ > - unsigned long timeout__ = jiffies + msecs_to_jiffies(MS); \ > + unsigned long timeout__ = jiffies + msecs_to_jiffies(MS) + 1; \ > int ret__ = 0; \ > while (!(COND)) { \ > if (time_after(jiffies, timeout__)) { \ > - ret__ = -ETIMEDOUT; \ > + if (!(COND)) \ > + ret__ = -ETIMEDOUT; \ > break; \ > } \ > if (W && drm_can_sleep()) { \ > -- > 1.7.11.7 > > _______________________________________________ > Intel-gfx mailing list > [email protected] > http://lists.freedesktop.org/mailman/listinfo/intel-gfx -- Ville Syrjälä Intel OTC _______________________________________________ Intel-gfx mailing list [email protected] http://lists.freedesktop.org/mailman/listinfo/intel-gfx
