From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 89FFF23B62B; Mon, 23 Mar 2026 20:28:30 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774297710; cv=none; b=LBLweTzRrVZRFQYuSmXC9vglCLLfVaCv4Q+Gh4/vJBwSeyuqaidYEUaIX4ipjiVXd91+Uc68IG3xiHV9wkQPlKNuER/1xHkvN7KYQQ/tm+bMGIqFiS5wCllxHxOXwuE6DhmdzCJQjaghICd7wWvGfB2LoaHeAdKWwRs/rsIghhU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774297710; c=relaxed/simple; bh=4HmpqGCnc/JeGi5fqb9LLF+uG4EQxB9xOBgK4+WfF/Q=; h=Date:Message-ID:From:To:Cc:Subject; b=Q2FTqcYXEim5/s9j4DOpcWMA68JK8fKj5BLQwk/Vo8wcA9DjcohSFq/AnaYW30Xn+36nhh/+qEdOjIPBFFS4n8NWgzZlfcr4ss5V2KosrBEDZugnVW1mBqToTsVivtnRM1cZ6LLN/VnXD2JCmYC1xHoZKD/1biqIJSv9eeNavTM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=jbO8WRc5; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="jbO8WRc5" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4FB64C4CEF7; Mon, 23 Mar 2026 20:28:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1774297710; bh=4HmpqGCnc/JeGi5fqb9LLF+uG4EQxB9xOBgK4+WfF/Q=; h=Date:From:To:Cc:Subject:From; b=jbO8WRc5iz9Eo5OTfuqyOljM7W6kP6Mk/j12QzvCor9p18ZUCweZ2PfRvPAZ8hF6P d815C2G8YJhQoQUdKf/f4f7U7BiZDwcpkWGXoCC5OCuhR0K4hQ2B0fuzsoVZnk8Yfn PCghewzpikBWv8HzumKtmAWnrxM23acdFjvtaKW3m6gIguDmZyLEjLRTQLzh87Njq3 pNNkXxK5mSUzA1icj53Y1hLA4nUPYL2luwMRXOW6dgy9oPR7eORHLGiBTXwHEbQ3t0 Lf+2fXhBykBmBhn7sg4Q16o82vNecUQm2xn7OI7iujZ8arcqZnepTSdFoCdpIJsyRG NYpL3fZrUbcSg== Date: Mon, 23 Mar 2026 10:28:29 -1000 Message-ID: <49dca9aa15c6c46de60f1ba4ef2b25d0@kernel.org> From: Tejun Heo To: cgroups@vger.kernel.org, linux-kernel@vger.kernel.org Cc: Sebastian Andrzej Siewior , Christian Brauner , Johannes Weiner , Michal Koutny , Shuah Khan , linux-kselftest@vger.kernel.org Subject: [PATCH cgroup/for-7.0-fixes] selftests/cgroup: Don't test populated synchrony against task exit Precedence: bulk X-Mailing-List: cgroups@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: test_cgcore_populated (test_core) and test_cgkill_{simple,tree,forkbomb} (test_kill) check cgroup.events "populated 0" immediately after reaping child tasks with waitpid(). This used to work because cgroup_task_exit() in do_exit() unlinked tasks from css_sets before exit_notify() woke up waitpid(). d245698d727a ("cgroup: Defer task cgroup unlink until after the task is done switching out") moved the unlink to cgroup_task_dead() in finish_task_switch(), which runs after exit_notify(). The populated counter is now decremented after the parent's waitpid() can return, so there is no longer a synchronous ordering guarantee. On PREEMPT_RT, where cgroup_task_dead() is further deferred through lazy irq_work, the race window is even larger. The synchronous populated transition was never part of the cgroup interface contract - it was an implementation artifact. Use cg_read_strcmp_wait() which retries for up to 1 second, matching what these tests actually need to verify: that the cgroup eventually becomes unpopulated after all tasks exit. Fixes: d245698d727a ("cgroup: Defer task cgroup unlink until after the task is done switching out") Reported-by: Sebastian Andrzej Siewior Signed-off-by: Tejun Heo Cc: Christian Brauner Cc: cgroups@vger.kernel.org --- tools/testing/selftests/cgroup/lib/cgroup_util.c | 15 +++++++++++++++ tools/testing/selftests/cgroup/lib/include/cgroup_util.h | 2 ++ tools/testing/selftests/cgroup/test_core.c | 3 ++- tools/testing/selftests/cgroup/test_kill.c | 7 ++++--- 4 files changed, 23 insertions(+), 4 deletions(-) --- a/tools/testing/selftests/cgroup/lib/cgroup_util.c +++ b/tools/testing/selftests/cgroup/lib/cgroup_util.c @@ -123,6 +123,21 @@ int cg_read_strcmp(const char *cgroup, c return ret; } +int cg_read_strcmp_wait(const char *cgroup, const char *control, + const char *expected) +{ + int i, ret; + + for (i = 0; i < 100; i++) { + ret = cg_read_strcmp(cgroup, control, expected); + if (!ret) + return ret; + usleep(10000); + } + + return ret; +} + int cg_read_strstr(const char *cgroup, const char *control, const char *needle) { char buf[PAGE_SIZE]; --- a/tools/testing/selftests/cgroup/lib/include/cgroup_util.h +++ b/tools/testing/selftests/cgroup/lib/include/cgroup_util.h @@ -61,6 +61,8 @@ extern int cg_read(const char *cgroup, c char *buf, size_t len); extern int cg_read_strcmp(const char *cgroup, const char *control, const char *expected); +extern int cg_read_strcmp_wait(const char *cgroup, const char *control, + const char *expected); extern int cg_read_strstr(const char *cgroup, const char *control, const char *needle); extern long cg_read_long(const char *cgroup, const char *control); --- a/tools/testing/selftests/cgroup/test_core.c +++ b/tools/testing/selftests/cgroup/test_core.c @@ -233,7 +233,8 @@ static int test_cgcore_populated(const c if (err) goto cleanup; - if (cg_read_strcmp(cg_test_d, "cgroup.events", "populated 0\n")) + if (cg_read_strcmp_wait(cg_test_d, "cgroup.events", + "populated 0\n")) goto cleanup; /* Remove cgroup. */ --- a/tools/testing/selftests/cgroup/test_kill.c +++ b/tools/testing/selftests/cgroup/test_kill.c @@ -86,7 +86,7 @@ cleanup: wait_for_pid(pids[i]); if (ret == KSFT_PASS && - cg_read_strcmp(cgroup, "cgroup.events", "populated 0\n")) + cg_read_strcmp_wait(cgroup, "cgroup.events", "populated 0\n")) ret = KSFT_FAIL; if (cgroup) @@ -190,7 +190,8 @@ cleanup: wait_for_pid(pids[i]); if (ret == KSFT_PASS && - cg_read_strcmp(cgroup[0], "cgroup.events", "populated 0\n")) + cg_read_strcmp_wait(cgroup[0], "cgroup.events", + "populated 0\n")) ret = KSFT_FAIL; for (i = 9; i >= 0 && cgroup[i]; i--) { @@ -251,7 +252,7 @@ cleanup: wait_for_pid(pid); if (ret == KSFT_PASS && - cg_read_strcmp(cgroup, "cgroup.events", "populated 0\n")) + cg_read_strcmp_wait(cgroup, "cgroup.events", "populated 0\n")) ret = KSFT_FAIL; if (cgroup)