Re: [Intel-gfx] [igt-dev] [PATCH i-g-t] i915/gem_ctx_exec: Exercise execution along context while closing it

[Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>]

On 04/12/2020 11:27, Chris Wilson wrote:
> Race the execution and interrupt handlers along a context, while
> closing it at a random time.
> 
> v2: Some comments to handwave away the knowledge of internal
> implementation details.
> 
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> ---
>   tests/i915/gem_ctx_exec.c | 84 +++++++++++++++++++++++++++++++++++++++
>   1 file changed, 84 insertions(+)
> 
> diff --git a/tests/i915/gem_ctx_exec.c b/tests/i915/gem_ctx_exec.c
> index 194191def..5c6109237 100644
> --- a/tests/i915/gem_ctx_exec.c
> +++ b/tests/i915/gem_ctx_exec.c
> @@ -43,6 +43,7 @@
>   #include "i915/gem.h"
>   #include "igt.h"
>   #include "igt_dummyload.h"
> +#include "igt_rand.h"
>   #include "igt_sysfs.h"
>   #include "sw_sync.h"
>   
> @@ -336,6 +337,86 @@ static void nohangcheck_hostile(int i915)
>   	close(i915);
>   }
>   
> +static void close_race(int i915)
> +{
> +	const int ncpus = sysconf(_SC_NPROCESSORS_ONLN);
> +	uint32_t *contexts;
> +
> +	contexts = mmap(NULL, 4096, PROT_WRITE, MAP_SHARED | MAP_ANON, -1, 0);
> +	igt_assert(contexts != MAP_FAILED);
> +
> +	for (int child = 0; child < ncpus; child++)
> +		contexts[child] = gem_context_clone_with_engines(i915, 0);
> +
> +	igt_fork(child, ncpus) {
> +		igt_spin_t *spin;
> +
> +		spin = igt_spin_new(i915, .flags = IGT_SPIN_POLL_RUN);
> +		igt_spin_end(spin);
> +		gem_sync(i915, spin->handle);
> +
> +		while (!READ_ONCE(contexts[ncpus])) {
> +			int64_t timeout = 1;
> +
> +			igt_spin_reset(spin);
> +			igt_assert(!igt_spin_has_started(spin));
> +
> +			spin->execbuf.rsvd1 = READ_ONCE(contexts[child]);
> +			if (__gem_execbuf(i915, &spin->execbuf))
> +				continue;
> +
> +			/*
> +			 * One race we are particularly interested in is the
> +			 * handling of interrupt signaling along a closed
> +			 * context. We want to see if we can catch the kernel
> +			 * freeing the context while using it in the interrupt
> +			 * handler.
> +			 *
> +			 * There's no API to mandate that the interrupt is
> +			 * generate for a wait, nor that the implementation
> +			 * details of the kernel will not change to remove
> +			 * context access during interrupt processing. But
> +			 * for now, this should be interesting.
> +			 *
> +			 * Even if the signaling implementation is changed,
> +			 * racing context closure versus execbuf and looking
> +			 * at the outcome is very useful.
> +			 */
> +
> +			igt_assert(gem_bo_busy(i915, spin->handle));
> +			gem_wait(i915, spin->handle, &timeout); /* prime irq */
> +			igt_spin_busywait_until_started(spin);
> +
> +			igt_spin_end(spin);
> +			gem_sync(i915, spin->handle);
> +		}
> +
> +		igt_spin_free(i915, spin);
> +	}
> +
> +	igt_until_timeout(5) {
> +		/*
> +		 * Recreate all the contexts while they are in active use
> +		 * by the children. This may race with any of their ioctls
> +		 * and the kernel's context/request handling.
> +		 */
> +		for (int child = 0; child < ncpus; child++) {
> +			gem_context_destroy(i915, contexts[child]);
> +			contexts[child] =
> +				gem_context_clone_with_engines(i915, 0);
> +		}
> +		usleep(1000 + hars_petruska_f54_1_random_unsafe() % 2000);
> +	}
> +
> +	contexts[ncpus] = 1;
> +	igt_waitchildren();
> +
> +	for (int child = 0; child < ncpus; child++)
> +		gem_context_destroy(i915, contexts[child]);
> +
> +	munmap(contexts, 4096);
> +}
> +
>   igt_main
>   {
>   	const uint32_t batch[2] = { 0, MI_BATCH_BUFFER_END };
> @@ -380,6 +461,9 @@ igt_main
>   	igt_subtest("basic-nohangcheck")
>   		nohangcheck_hostile(fd);
>   
> +	igt_subtest("basic-close-race")
> +		close_race(fd);
> +
>   	igt_subtest("reset-pin-leak") {
>   		int i;
>   
> 

Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>

Regards,

Tvrtko
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