linux-kernel - [PATCH 15/22] selftests/coredump: fix userspace coredump client detection

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Message-Id: <20251028-work-coredump-signal-v1-15-ca449b7b7aa0@kernel.org>
Date: Tue, 28 Oct 2025 09:46:00 +0100
From: Christian Brauner <brauner@...nel.org>
To: linux-fsdevel@...r.kernel.org
Cc: Oleg Nesterov <oleg@...hat.com>, Amir Goldstein <amir73il@...il.com>, 
 Aleksa Sarai <cyphar@...har.com>, 
 Yu Watanabe <watanabe.yu+github@...il.com>, 
 Josef Bacik <josef@...icpanda.com>, Jeff Layton <jlayton@...nel.org>, 
 Jann Horn <jannh@...gle.com>, Luca Boccassi <luca.boccassi@...il.com>, 
 Alexander Mikhalitsyn <alexander@...alicyn.com>, 
 linux-kernel@...r.kernel.org, Alexander Viro <viro@...iv.linux.org.uk>, 
 Jan Kara <jack@...e.cz>, Lennart Poettering <lennart@...ttering.net>, 
 Mike Yuan <me@...dnzj.com>, 
 Zbigniew Jędrzejewski-Szmek <zbyszek@...waw.pl>, 
 Christian Brauner <brauner@...nel.org>
Subject: [PATCH 15/22] selftests/coredump: fix userspace coredump client
 detection

PIDFD_INFO_COREDUMP is only retrievable until the task has exited. After
it has exited task->mm is NULL. So if the task didn't actually coredump
we can't retrieve it's dumpability settings anymore. Only if the task
did coredump will we have stashed the coredump information in the
respective struct pid.

Signed-off-by: Christian Brauner <brauner@...nel.org>
---
 tools/testing/selftests/coredump/coredump_socket_test.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/tools/testing/selftests/coredump/coredump_socket_test.c b/tools/testing/selftests/coredump/coredump_socket_test.c
index 658f3966064f..5103d9f13003 100644
--- a/tools/testing/selftests/coredump/coredump_socket_test.c
+++ b/tools/testing/selftests/coredump/coredump_socket_test.c
@@ -271,22 +271,26 @@ TEST_F(coredump, socket_detect_userspace_client)
 			_exit(EXIT_FAILURE);
 
 		close(fd_socket);
+		pause();
 		_exit(EXIT_SUCCESS);
 	}
 
 	pidfd = sys_pidfd_open(pid, 0);
 	ASSERT_GE(pidfd, 0);
 
-	waitpid(pid, &status, 0);
-	ASSERT_TRUE(WIFEXITED(status));
-	ASSERT_EQ(WEXITSTATUS(status), 0);
-
 	ASSERT_TRUE(get_pidfd_info(pidfd, &info));
 	ASSERT_GT((info.mask & PIDFD_INFO_COREDUMP), 0);
 	ASSERT_EQ((info.coredump_mask & PIDFD_COREDUMPED), 0);
 
 	wait_and_check_coredump_server(pid_coredump_server, _metadata, self);
 
+	ASSERT_EQ(sys_pidfd_send_signal(pidfd, SIGKILL, NULL, 0), 0);
+	ASSERT_EQ(close(pidfd), 0);
+
+	waitpid(pid, &status, 0);
+	ASSERT_TRUE(WIFSIGNALED(status));
+	ASSERT_EQ(WTERMSIG(status), SIGKILL);
+
 	ASSERT_NE(stat("/tmp/coredump.file", &st), 0);
 	ASSERT_EQ(errno, ENOENT);
 }

-- 
2.47.3