linux-kernel - [PATCH v2 3/5] userfaultfd/selftests: Dropping VERIFY check in locking

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Message-Id: <20210412232753.1012412-4-peterx@redhat.com>
Date:   Mon, 12 Apr 2021 19:27:51 -0400
From:   Peter Xu <peterx@...hat.com>
To:     linux-mm@...ck.org, linux-kernel@...r.kernel.org
Cc:     Andrea Arcangeli <aarcange@...hat.com>, peterx@...hat.com,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        Axel Rasmussen <axelrasmussen@...gle.com>
Subject: [PATCH v2 3/5] userfaultfd/selftests: Dropping VERIFY check in locking_thread

It tries to check against all zeros and looped for quite a few times.  However
after that we'll verify the same page with count_verify, while count_verify can
never be zero.  So it means if it's a zero page we'll detect it anyways with
below code.

There's yet another place we conditionally check the fault flag - just do it
unconditionally.

Reviewed-by: Axel Rasmussen <axelrasmussen@...gle.com>
Signed-off-by: Peter Xu <peterx@...hat.com>
---
 tools/testing/selftests/vm/userfaultfd.c | 55 +-----------------------
 1 file changed, 1 insertion(+), 54 deletions(-)

diff --git a/tools/testing/selftests/vm/userfaultfd.c b/tools/testing/selftests/vm/userfaultfd.c
index 5cae66e27171..387b9360ae64 100644
--- a/tools/testing/selftests/vm/userfaultfd.c
+++ b/tools/testing/selftests/vm/userfaultfd.c
@@ -430,58 +430,6 @@ static void *locking_thread(void *arg)
 		} else
 			page_nr += 1;
 		page_nr %= nr_pages;
-
-		if (bounces & BOUNCE_VERIFY) {
-			count = *area_count(area_dst, page_nr);
-			if (!count) {
-				fprintf(stderr,
-					"page_nr %lu wrong count %Lu %Lu\n",
-					page_nr, count,
-					count_verify[page_nr]);
-				exit(1);
-			}
-
-
-			/*
-			 * We can't use bcmp (or memcmp) because that
-			 * returns 0 erroneously if the memory is
-			 * changing under it (even if the end of the
-			 * page is never changing and always
-			 * different).
-			 */
-#if 1
-			if (!my_bcmp(area_dst + page_nr * page_size, zeropage,
-				     page_size)) {
-				fprintf(stderr,
-					"my_bcmp page_nr %lu wrong count %Lu %Lu\n",
-					page_nr, count, count_verify[page_nr]);
-				exit(1);
-			}
-#else
-			unsigned long loops;
-
-			loops = 0;
-			/* uncomment the below line to test with mutex */
-			/* pthread_mutex_lock(area_mutex(area_dst, page_nr)); */
-			while (!bcmp(area_dst + page_nr * page_size, zeropage,
-				     page_size)) {
-				loops += 1;
-				if (loops > 10)
-					break;
-			}
-			/* uncomment below line to test with mutex */
-			/* pthread_mutex_unlock(area_mutex(area_dst, page_nr)); */
-			if (loops) {
-				fprintf(stderr,
-					"page_nr %lu all zero thread %lu %p %lu\n",
-					page_nr, cpu, area_dst + page_nr * page_size,
-					loops);
-				if (loops > 10)
-					exit(1);
-			}
-#endif
-		}
-
 		pthread_mutex_lock(area_mutex(area_dst, page_nr));
 		count = *area_count(area_dst, page_nr);
 		if (count != count_verify[page_nr]) {
@@ -613,8 +561,7 @@ static void uffd_handle_page_fault(struct uffd_msg *msg,
 		stats->minor_faults++;
 	} else {
 		/* Missing page faults */
-		if (bounces & BOUNCE_VERIFY &&
-		    msg->arg.pagefault.flags & UFFD_PAGEFAULT_FLAG_WRITE) {
+		if (msg->arg.pagefault.flags & UFFD_PAGEFAULT_FLAG_WRITE) {
 			fprintf(stderr, "unexpected write fault\n");
 			exit(1);
 		}
-- 
2.26.2