Quoting Tvrtko Ursulin (2018-05-17 11:27:20)
> 
> On 17/05/2018 08:40, Chris Wilson wrote:
> > As we want to be able to call i915_reset_engine and co from a softirq or
> 
> Just by glancing i915_reset_engine looks to heavy weight to ever be 
> callable from softirq/timer context. There is even a flush_workqueue in 
> there.

There isn't by the time we finish :)

> > timer context, we need to be irqsafe at all timers. So we have to forgo
> > the simple spin_lock_irq for the full spin_lock_irqsave.
> > 
> > Signed-off-by: Chris Wilson <ch...@chris-wilson.co.uk>
> > ---
> >   drivers/gpu/drm/i915/i915_gem.c | 6 ++++--
> >   1 file changed, 4 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/i915_gem.c 
> > b/drivers/gpu/drm/i915/i915_gem.c
> > index 03874b50ada9..a3885adec78a 100644
> > --- a/drivers/gpu/drm/i915/i915_gem.c
> > +++ b/drivers/gpu/drm/i915/i915_gem.c
> > @@ -3137,15 +3137,17 @@ i915_gem_reset_request(struct intel_engine_cs 
> > *engine,
> 
> Or you meant to write i915_gem_reset_request / i915_gem_reset_engine in 
> the commit message?

static int try_preempt_reset(struct intel_engine_execlists *execlists)
{
        struct tasklet_struct * const t = &execlists->tasklet;
        int err = -EBUSY;

        if (tasklet_trylock(t)) {
                struct intel_engine_cs *engine =
                        container_of(execlists, typeof(*engine), execlists);
                const unsigned int bit = I915_RESET_ENGINE + engine->id;
                unsigned long *lock = &engine->i915->gpu_error.flags;

                t->func(t->data);
                if (!execlists_is_active(execlists,
                                         EXECLISTS_ACTIVE_PREEMPT_TIMEOUT)) {
                        /* Nothing to do; the tasklet was just delayed. */
                        err = 0;
                } else if (!test_and_set_bit(bit, lock)) {
                        tasklet_disable_nosync(t);
                        err = i915_reset_engine(engine, "preemption time out");
                        tasklet_enable(t);

                        clear_bit(bit, lock);
                        wake_up_bit(lock, bit);
                }

                tasklet_unlock(t);
        }

        return err;
}

is what I'm aiming for.

And even a test case to call it in irq-off and other atomic contexts.
-Chris
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