Subject: Re: [PATCH 2/2] selftests/powerpc: Test the THP bug we fixed in the previous commit

From: "Aneesh Kumar K.V" <[email-masked]>
Date: Wed, 28 May 2014 14:57:23 +0530

Michael Ellerman <[email-masked]> writes:

> Signed-off-by: Michael Ellerman <[email-masked]>

Reviewed-by: Aneesh Kumar K.V <[email-masked]>

> ---
>  tools/testing/selftests/powerpc/Makefile           |  2 +-
>  tools/testing/selftests/powerpc/mm/Makefile        | 18 ++++++
>  .../selftests/powerpc/mm/hugetlb_vs_thp_test.c     | 72 ++++++++++++++++++++++
>  3 files changed, 91 insertions(+), 1 deletion(-)
>  create mode 100644 tools/testing/selftests/powerpc/mm/Makefile
>  create mode 100644 tools/testing/selftests/powerpc/mm/hugetlb_vs_thp_test.c
>
> diff --git a/tools/testing/selftests/powerpc/Makefile b/tools/testing/selftests/powerpc/Makefile
> index 316194f..b3dbe9e 100644
> --- a/tools/testing/selftests/powerpc/Makefile
> +++ b/tools/testing/selftests/powerpc/Makefile
> @@ -13,7 +13,7 @@ CFLAGS := -Wall -O2 -flto -Wall -Werror -DGIT_VERSION='"$(GIT_VERSION)"' -I$(CUR
>  
>  export CC CFLAGS
>  
> -TARGETS = pmu copyloops
> +TARGETS = pmu copyloops mm
>  
>  endif
>  
> diff --git a/tools/testing/selftests/powerpc/mm/Makefile b/tools/testing/selftests/powerpc/mm/Makefile
> new file mode 100644
> index 0000000..357ccbd
> --- /dev/null
> +++ b/tools/testing/selftests/powerpc/mm/Makefile
> @@ -0,0 +1,18 @@
> +noarg:
> +	$(MAKE) -C ../
> +
> +PROGS := hugetlb_vs_thp_test
> +
> +all: $(PROGS)
> +
> +$(PROGS): ../harness.c
> +
> +run_tests: all
> +	@-for PROG in $(PROGS); do \
> +		./$$PROG; \
> +	done;
> +
> +clean:
> +	rm -f $(PROGS)
> +
> +.PHONY: all run_tests clean
> diff --git a/tools/testing/selftests/powerpc/mm/hugetlb_vs_thp_test.c b/tools/testing/selftests/powerpc/mm/hugetlb_vs_thp_test.c
> new file mode 100644
> index 0000000..3d8e5b0
> --- /dev/null
> +++ b/tools/testing/selftests/powerpc/mm/hugetlb_vs_thp_test.c
> @@ -0,0 +1,72 @@
> +#include <stdio.h>
> +#include <sys/mman.h>
> +#include <unistd.h>
> +
> +#include "utils.h"
> +
> +/* This must match the huge page & THP size */
> +#define SIZE	(16 * 1024 * 1024)
> +
> +static int test_body(void)
> +{
> +	void *addr;
> +	char *p;
> +
> +	addr = (void *)0xa0000000;
> +
> +	p = mmap(addr, SIZE, PROT_READ | PROT_WRITE,
> +		 MAP_HUGETLB | MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
> +	if (p != MAP_FAILED) {
> +		/*
> +		 * Typically the mmap will fail because no huge pages are
> +		 * allocated on the system. But if there are huge pages
> +		 * allocated the mmap will succeed. That's fine too, we just
> +		 * munmap here before continuing.
> +		 */
> +		munmap(addr, SIZE);
> +	}
> +
> +	p = mmap(addr, SIZE, PROT_READ | PROT_WRITE,
> +		 MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
> +	if (p == MAP_FAILED) {
> +		printf("Mapping failed @ %p\n", addr);
> +		perror("mmap");
> +		return 1;
> +	}
> +
> +	/*
> +	 * Either a user or kernel access is sufficient to trigger the bug.
> +	 * A kernel access is easier to spot & debug, as it will trigger the
> +	 * softlockup or RCU stall detectors, and when the system is kicked
> +	 * into xmon we get a backtrace in the kernel.
> +	 *
> +	 * A good option is:
> +	 *  getcwd(p, SIZE);
> +	 *
> +	 * For the purposes of this testcase it's preferable to spin in
> +	 * userspace, so the harness can kill us if we get stuck. That way we
> +	 * see a test failure rather than a dead system.
> +	 */
> +	*p = 0xf;
> +
> +	munmap(addr, SIZE);
> +
> +	return 0;
> +}
> +
> +static int test_main(void)
> +{
> +	int i;
> +
> +	/* 10,000 because it's a "bunch", and completes reasonably quickly */
> +	for (i = 0; i < 10000; i++)
> +		if (test_body())
> +			return 1;
> +
> +	return 0;
> +}
> +
> +int main(void)
> +{
> +	return test_harness(test_main, "hugetlb_vs_thp");
> +}
> -- 
> 1.9.1
>
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