[PATCH 2/2] selftests/user_events: wait for deferred event teardown after unregister
From: Michael Bommarito <hidden>
Date: 2026-07-07 16:59:30
Also in:
lkml, stable
Subsystem:
kernel selftest framework, the rest · Maintainers:
Shuah Khan, Linus Torvalds
Unregistering a user event now defers the drop of the enabler's event
reference (and the freeing of the enabler) past an RCU grace period. As a
result DIAG_IOCSDEL can transiently fail with -EBUSY while that last
reference is still being dropped, where it previously succeeded
immediately.
Two tests assumed the delete takes effect the instant the unregister
returns:
- abi_test "flags" deletes the event right after disabling it.
- perf_test's fixture teardown clear() deletes __test_event before the
next test registers the same name; a stale event makes the following
registration fail with -EADDRINUSE.
Retry the delete until it succeeds (or the event is already gone) with a
bounded wait, matching the existing wait_for_delete() idiom in the same
suite, so the tests are robust to the deferred teardown.
Assisted-by: Claude:claude-opus-4-8
Signed-off-by: Michael Bommarito <redacted>
---
.../testing/selftests/user_events/abi_test.c | 24 ++++++++++++++++-
.../testing/selftests/user_events/perf_test.c | 26 ++++++++++++++++---
2 files changed, 46 insertions(+), 4 deletions(-)
diff --git a/tools/testing/selftests/user_events/abi_test.c b/tools/testing/selftests/user_events/abi_test.c
index 85892b3b719cc..9e2f84d281afc 100644
--- a/tools/testing/selftests/user_events/abi_test.c
+++ b/tools/testing/selftests/user_events/abi_test.c@@ -132,6 +132,28 @@ static int event_delete(void) return ret; } +/* + * Deleting an event drops its last reference, but an unregister may defer + * that put (and the freeing of the associated enabler) past an RCU grace + * period. The delete can therefore transiently fail with -EBUSY while the + * previous reference is still being dropped. Retry for up to ~10 seconds. + */ +static int wait_for_event_delete(void) +{ + int i, ret; + + for (i = 0; i < 10000; ++i) { + ret = event_delete(); + + if (ret == 0) + return 0; + + usleep(1000); + } + + return ret; +} + static int reg_enable_multi(void *enable, int size, int bit, int flags, char *args) {
@@ -262,7 +284,7 @@ TEST_F(user, flags) { ASSERT_TRUE(event_exists()); /* Ensure we can delete it */ - ASSERT_EQ(0, event_delete()); + ASSERT_EQ(0, wait_for_event_delete()); /* USER_EVENT_REG_MAX or above is not allowed */ ASSERT_EQ(-1, reg_enable_flags(&self->check, sizeof(int), 0,
diff --git a/tools/testing/selftests/user_events/perf_test.c b/tools/testing/selftests/user_events/perf_test.c
index cafec0e52eb31..5727cb5b914cf 100644
--- a/tools/testing/selftests/user_events/perf_test.c
+++ b/tools/testing/selftests/user_events/perf_test.c@@ -85,6 +85,7 @@ static int get_offset(void) static int clear(int *check) { struct user_unreg unreg = {0}; + int i, ret; unreg.size = sizeof(unreg); unreg.disable_bit = 31;
@@ -99,13 +100,32 @@ static int clear(int *check) if (errno != ENOENT) return -1; - if (ioctl(fd, DIAG_IOCSDEL, "__test_event") == -1) - if (errno != ENOENT) + /* + * Deleting the event drops its last reference, but the unregister + * above defers that put (and the freeing of the enabler) past an RCU + * grace period. The delete can therefore transiently fail with -EBUSY + * until that reference is dropped. Retry for up to ~10 seconds so the + * event is actually gone before the next test registers the same name. + */ + for (i = 0; i < 10000; ++i) { + ret = ioctl(fd, DIAG_IOCSDEL, "__test_event"); + + if (ret == 0 || errno == ENOENT) { + ret = 0; + break; + } + + if (errno != EBUSY) { + close(fd); return -1; + } + + usleep(1000); + } close(fd); - return 0; + return ret; } FIXTURE(user) {
--
2.53.0