> -----Original Message-----
> From: Chris Wilson [mailto:[email protected]]
> Sent: Wednesday, December 6, 2017 7:38 AM
> To: [email protected]
> Cc: Chris Wilson <[email protected]>; Bloomfield, Jon
> <[email protected]>; Harrison, John C <[email protected]>;
> Ursulin, Tvrtko <[email protected]>; Joonas Lahtinen
> <[email protected]>; Daniel Vetter <[email protected]>
> Subject: [PATCH v2] drm/i915: Prevent machine hang from Broxton's vtd w/a
> and error capture
>
> Since capturing the error state requires fiddling around with the GGTT
> to read arbitrary buffers and is itself run under stop_machine(), it
> deadlocks the machine (effectively a hard hang) when run in conjunction
> with Broxton's VTd workaround to serialize GGTT access.
>
> v2: Store the ERR_PTR in first_error so that the error can be reported
> to the user via sysfs.
>
> Fixes: 0ef34ad6222a ("drm/i915: Serialize GTT/Aperture accesses on BXT")
> Signed-off-by: Chris Wilson <[email protected]>
> Cc: Jon Bloomfield <[email protected]>
> Cc: John Harrison <[email protected]>
> Cc: Tvrtko Ursulin <[email protected]>
> Cc: Joonas Lahtinen <[email protected]>
> Cc: Daniel Vetter <[email protected]>
It's a real shame to lose error capture on BXT. Can we wrap stop_machine to
make it recursive ?
Something like...
static cpumask_t sm_mask;
struct sm_args {
cpu_stop_fn_t *fn;
void *data;
};
void do_recursive_stop(void *sm_arg_data)
{
struct sm_arg *args = sm_arg_data;
/* We're stopped - flag the fact to prevent recursion */
cpumask_set_cpu(smp_processor_id(), &sm_mask);
args->fn(args->data);
/* Re-enable recursion */
cpumask_clear_cpu(smp_processor_id(), &sm_mask);
}
void recursive_stop_machine(cpu_stop_fn_t fn, void *data)
{
if (cpumask_test_cpu(smp_processor_id(), &sm_mask)) {
/* We were already stopped, so can just call directly */
fn(data);
}
else {
/* Our CPU is not currently stopped */
struct sm_args *args = {fn, data};
stop_machine(do_recursive_stop, args, NULL);
}
}
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