linux-kernel - [PATCH v2 2/5] userfaultfd/selftests: Remove the time() check on delayed uffd

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Message-Id: <20210412232753.1012412-3-peterx@redhat.com>
Date:   Mon, 12 Apr 2021 19:27:50 -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 2/5] userfaultfd/selftests: Remove the time() check on delayed uffd

There seems to have no guarantee that time() will return the same for the two
calls even if there's no delay, e.g. when a fault is accidentally crossing the
changing of a second.  Meanwhile, this message is also not helping that much
since delay could happen with a lot of reasons, e.g., schedule latency of
resolving thread.  It may not mean an issue with uffd.

Neither do I saw this error triggered either in the past runs.  Even if it
triggers, it'll be drown in all the rest of test logs.  Remove it.

Reviewed-by: Axel Rasmussen <axelrasmussen@...gle.com>
Signed-off-by: Peter Xu <peterx@...hat.com>
---
 tools/testing/selftests/vm/userfaultfd.c | 8 --------
 1 file changed, 8 deletions(-)

diff --git a/tools/testing/selftests/vm/userfaultfd.c b/tools/testing/selftests/vm/userfaultfd.c
index ce23db8eec26..5cae66e27171 100644
--- a/tools/testing/selftests/vm/userfaultfd.c
+++ b/tools/testing/selftests/vm/userfaultfd.c
@@ -395,7 +395,6 @@ static void *locking_thread(void *arg)
 	unsigned long long count;
 	char randstate[64];
 	unsigned int seed;
-	time_t start;
 
 	if (bounces & BOUNCE_RANDOM) {
 		seed = (unsigned int) time(NULL) - bounces;
@@ -432,7 +431,6 @@ static void *locking_thread(void *arg)
 			page_nr += 1;
 		page_nr %= nr_pages;
 
-		start = time(NULL);
 		if (bounces & BOUNCE_VERIFY) {
 			count = *area_count(area_dst, page_nr);
 			if (!count) {
@@ -495,12 +493,6 @@ static void *locking_thread(void *arg)
 		count++;
 		*area_count(area_dst, page_nr) = count_verify[page_nr] = count;
 		pthread_mutex_unlock(area_mutex(area_dst, page_nr));
-
-		if (time(NULL) - start > 1)
-			fprintf(stderr,
-				"userfault too slow %ld "
-				"possible false positive with overcommit\n",
-				time(NULL) - start);
 	}
 
 	return NULL;
-- 
2.26.2