From: Joe Lawrence <joe.lawrence@redhat.com>
To: live-patching@vger.kernel.org
Cc: Joe Lawrence <joe.lawrence@redhat.com>,
Miroslav Benes <mbenes@suse.cz>, Petr Mladek <pmladek@suse.com>,
Yannick Cote <ycote@suse.com>
Subject: [PATCH] selftests/livepatch: better synchronize test_klp_callbacks_busy
Date: Wed, 18 May 2022 13:34:24 -0400 [thread overview]
Message-ID: <20220518173424.911649-1-joe.lawrence@redhat.com> (raw)
The test_klp_callbacks_busy module conditionally blocks a future
livepatch transition by busy waiting inside its workqueue function,
busymod_work_func(). After scheduling this work, a test livepatch is
loaded, introducing the transition under test.
Both events are marked in the kernel log for later verification, but
there is no synchronization to ensure that busymod_work_func() logs its
function entry message before subsequent selftest commands log their own
messages. This can lead to a rare test failure due to unexpected
ordering like:
--- expected
+++ result
@@ -1,7 +1,7 @@
% modprobe test_klp_callbacks_busy block_transition=Y
test_klp_callbacks_busy: test_klp_callbacks_busy_init
-test_klp_callbacks_busy: busymod_work_func enter
% modprobe test_klp_callbacks_demo
+test_klp_callbacks_busy: busymod_work_func enter
livepatch: enabling patch 'test_klp_callbacks_demo'
livepatch: 'test_klp_callbacks_demo': initializing patching transition
test_klp_callbacks_demo: pre_patch_callback: vmlinux
Force the module init function to wait until busymod_work_func() has
started (and logged its message), before exiting to the next selftest
steps.
Fixes: 547840bd5ae5 ("selftests/livepatch: simplify test-klp-callbacks busy target tests")
Signed-off-by: Joe Lawrence <joe.lawrence@redhat.com>
---
Hi Petr, I remember you discouraged against a completion variable the
first time around [1], but is there any better way with the workqueue
API to ensure our "enter" message gets logged first? Or should we just
drop the msg altogether to avoid the situation? I don't think it's
absolutely necessary for the tests.
[1] https://lore.kernel.org/live-patching/20200602081654.GI27273@linux-b0ei/
lib/livepatch/test_klp_callbacks_busy.c | 7 +++++++
1 file changed, 7 insertions(+)
diff --git a/lib/livepatch/test_klp_callbacks_busy.c b/lib/livepatch/test_klp_callbacks_busy.c
index 7ac845f65be5..eb502b2bb3ef 100644
--- a/lib/livepatch/test_klp_callbacks_busy.c
+++ b/lib/livepatch/test_klp_callbacks_busy.c
@@ -16,10 +16,16 @@ MODULE_PARM_DESC(block_transition, "block_transition (default=false)");
static void busymod_work_func(struct work_struct *work);
static DECLARE_WORK(work, busymod_work_func);
+static DECLARE_COMPLETION(busymod_work_started);
static void busymod_work_func(struct work_struct *work)
{
+ /*
+ * Hold the init function from exiting until we've started and
+ * announced our appearence in the kernel log.
+ */
pr_info("%s enter\n", __func__);
+ complete(&busymod_work_started);
while (READ_ONCE(block_transition)) {
/*
@@ -36,6 +42,7 @@ static int test_klp_callbacks_busy_init(void)
{
pr_info("%s\n", __func__);
schedule_work(&work);
+ wait_for_completion(&busymod_work_started);
if (!block_transition) {
/*
--
2.26.3
next reply other threads:[~2022-05-18 17:34 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-05-18 17:34 Joe Lawrence [this message]
2022-05-18 18:18 ` [PATCH] selftests/livepatch: better synchronize test_klp_callbacks_busy Joe Lawrence
2022-05-23 15:28 ` Petr Mladek
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