From nobody Tue Feb 10 18:21:28 2026 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 5C25F1EA7EA for ; Wed, 19 Feb 2025 13:01:01 +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=1739970062; cv=none; b=qtmus0bcU67KqRd8wJHbTBqhq9SnYGTOc7rQ533X35ujz94pSue42D5RwnzFki38tfI8Wa/cZLLsJWSvamWZy0/dycznZ0lC6PFTRYMPbVBOVybqS4pLAscEOIybU2NMkEwb5NJz4+AZoPYFV0NNSJ6u7Xe/cuUtxYhPt8rv3gc= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1739970062; c=relaxed/simple; bh=yRt/VaZXQuh0DYvzuCq9THX6LnIgF5KQbpuqcMQ4SZs=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=fsQ6t/14XaEROZT++0mpUTkpLtAUsNpPz8JuSPR9AKBDU6y2a43ry8150Xlvu1kSg/v+bZcERsNUIG/kdntV2TINPl0tTLqtVtXQ2s8Wq4T6JTKP31laMFWR+H79fVz/FMPycohDBL7j/SekWD0+yzSqn+L1J7QNrIbZCMI9cfk= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=lCcnFldD; 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="lCcnFldD" Received: by smtp.kernel.org (Postfix) with ESMTPSA id D690CC4CED1; Wed, 19 Feb 2025 13:00:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1739970061; bh=yRt/VaZXQuh0DYvzuCq9THX6LnIgF5KQbpuqcMQ4SZs=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=lCcnFldD0m+q/ylAlrkWh8wDO68zQUs+Fhb+80rATiw1vEBeLLczY8edQtLr6IImG 3BbLY0OILVuMSdiVFvaCkfG2IW/YwW2X2/iLIQl7Eff8xpp6PEODAgnvaeFPQIoo+e jNzEUCsNInV4iAX3kznlG26MnJ6DwpVRWH9LlqfNRXMLDJnsE7B+8LdZkC+MkpJZna KVRNSBPjgMPUij2X33DD4DdOuqDYRc++Gkzvc3ZmWLQc5bMdXHhHkN4iU/r0lzOT07 PyU/m/hL+YmuAOWIc8bS58GlQQ7MPTl1x9lNgkQA6pKJedBDf7d8hc88Gz7kqBDv7J bKUS9OnwgPNWQ== From: "Masami Hiramatsu (Google)" To: Peter Zijlstra , Ingo Molnar , Will Deacon , Andrew Morton Cc: Boqun Feng , Waiman Long , Joel Granados , Masami Hiramatsu , Anna Schumaker , Lance Yang , Kent Overstreet , Yongliang Gao , Steven Rostedt , Tomasz Figa , Sergey Senozhatsky , linux-kernel@vger.kernel.org Subject: [PATCH 2/2] samples: Add hung_task detector mutex blocking sample Date: Wed, 19 Feb 2025 22:00:58 +0900 Message-ID: <173997005819.2137198.2020111976324308587.stgit@mhiramat.tok.corp.google.com> X-Mailer: git-send-email 2.48.1.601.g30ceb7b040-goog In-Reply-To: <173997003868.2137198.9462617208992136056.stgit@mhiramat.tok.corp.google.com> References: <173997003868.2137198.9462617208992136056.stgit@mhiramat.tok.corp.google.com> User-Agent: StGit/0.19 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable From: Masami Hiramatsu (Google) Add a hung_task detector mutex blocking test sample code. This module will create a dummy file on the debugfs. That file will cause the read process to sleep for enough long time (256 seconds) while holding a mutex. As a result, the second process will wait on the mutex for a prolonged duration and be detected by the hung_task detector. Usage is; > cd /sys/kernel/debug/hung_task > cat mutex & cat mutex and wait for hung_task message. Signed-off-by: Masami Hiramatsu (Google) --- samples/Kconfig | 9 +++++ samples/Makefile | 1 + samples/hung_task/Makefile | 2 + samples/hung_task/hung_task_mutex.c | 66 +++++++++++++++++++++++++++++++= ++++ 4 files changed, 78 insertions(+) create mode 100644 samples/hung_task/Makefile create mode 100644 samples/hung_task/hung_task_mutex.c diff --git a/samples/Kconfig b/samples/Kconfig index 820e00b2ed68..09011be2391a 100644 --- a/samples/Kconfig +++ b/samples/Kconfig @@ -300,6 +300,15 @@ config SAMPLE_CHECK_EXEC demonstrate how they should be used with execveat(2) + AT_EXECVE_CHECK. =20 +config SAMPLE_HUNG_TASK + tristate "Hung task detector test code" + depends on DETECT_HUNG_TASK && DEBUG_FS + help + Build a module which provide a simple debugfs file. If user reads + the file, it will sleep long time (256 seconds) with holding a + mutex. Thus if there are 2 or more processes read this file, it + will be detected by the hung_task watchdog. + source "samples/rust/Kconfig" =20 source "samples/damon/Kconfig" diff --git a/samples/Makefile b/samples/Makefile index f24cd0d72dd0..bf6e6fca5410 100644 --- a/samples/Makefile +++ b/samples/Makefile @@ -42,3 +42,4 @@ obj-$(CONFIG_SAMPLE_FPROBE) +=3D fprobe/ obj-$(CONFIG_SAMPLES_RUST) +=3D rust/ obj-$(CONFIG_SAMPLE_DAMON_WSSE) +=3D damon/ obj-$(CONFIG_SAMPLE_DAMON_PRCL) +=3D damon/ +obj-$(CONFIG_SAMPLE_HUNG_TASK) +=3D hung_task/ diff --git a/samples/hung_task/Makefile b/samples/hung_task/Makefile new file mode 100644 index 000000000000..fe9dde799880 --- /dev/null +++ b/samples/hung_task/Makefile @@ -0,0 +1,2 @@ +# SPDX-License-Identifier: GPL-2.0-only +obj-$(CONFIG_SAMPLE_HUNG_TASK) +=3D hung_task_mutex.o \ No newline at end of file diff --git a/samples/hung_task/hung_task_mutex.c b/samples/hung_task/hung_t= ask_mutex.c new file mode 100644 index 000000000000..7a29f2246d22 --- /dev/null +++ b/samples/hung_task/hung_task_mutex.c @@ -0,0 +1,66 @@ +// SPDX-License-Identifier: GPL-2.0-or-later +/* + * hung_task_mutex.c - Sample code which causes hung task by mutex + * + * Usage: load this module and read `/hung_task/mutex` + * by 2 or more processes. + * + * This is for testing kernel hung_task error message. + * Note that this will make your system freeze and maybe + * cause panic. So do not use this except for the test. + */ + +#include +#include +#include +#include +#include + +#define HUNG_TASK_DIR "hung_task" +#define HUNG_TASK_FILE "mutex" +#define SLEEP_SECOND 256 + +static const char dummy_string[] =3D "This is a dummy string."; +static DEFINE_MUTEX(dummy_mutex); +struct dentry *hung_task_dir; + +static ssize_t read_dummy(struct file *file, char __user *user_buf, + size_t count, loff_t *ppos) +{ + /* If the second task waits on the lock, it is uninterruptible sleep. */ + guard(mutex)(&dummy_mutex); + + /* When the first task sleep here, it is interruptible. */ + msleep_interruptible(SLEEP_SECOND * 1000); + + return simple_read_from_buffer(user_buf, count, ppos, + dummy_string, sizeof(dummy_string)); +} + +static const struct file_operations hung_task_fops =3D { + .read =3D read_dummy, +}; + +static int __init hung_task_sample_init(void) +{ + hung_task_dir =3D debugfs_create_dir(HUNG_TASK_DIR, NULL); + if (IS_ERR(hung_task_dir)) + return PTR_ERR(hung_task_dir); + + debugfs_create_file(HUNG_TASK_FILE, 0400, hung_task_dir, + NULL, &hung_task_fops); + + return 0; +} + +static void __exit hung_task_sample_exit(void) +{ + debugfs_remove_recursive(hung_task_dir); +} + +module_init(hung_task_sample_init); +module_exit(hung_task_sample_exit); + +MODULE_LICENSE("GPL"); +MODULE_AUTHOR("Masami Hiramatsu"); +MODULE_DESCRIPTION("Simple sleep under mutex file for testing hung task");