| lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
|
Open Source and information security mailing list archives
| ||
|
Message-ID: <20250314144300.32542-4-ioworker0@gmail.com>
Date: Fri, 14 Mar 2025 22:43:00 +0800
From: Lance Yang <ioworker0@...il.com>
To: akpm@...ux-foundation.org
Cc: will@...nel.org,
peterz@...radead.org,
mingo@...hat.com,
longman@...hat.com,
mhiramat@...nel.org,
anna.schumaker@...cle.com,
boqun.feng@...il.com,
joel.granados@...nel.org,
kent.overstreet@...ux.dev,
leonylgao@...cent.com,
linux-kernel@...r.kernel.org,
rostedt@...dmis.org,
senozhatsky@...omium.org,
tfiga@...omium.org,
amaindex@...look.com,
Lance Yang <ioworker0@...il.com>
Subject: [PATCH RESEND v2 3/3] samples: add hung_task detector semaphore blocking sample
From: Zi Li <amaindex@...look.com>
Add a hung_task detector semaphore blocking test sample code.
This module will create a dummy file on the debugfs. That file will cause
the read process to sleep for a sufficiently long time (256 seconds)
while holding a semaphore. As a result, the second process will wait on
the semaphore for a prolonged duration and be detected by the hung_task
detector.
Usage is;
> cd /sys/kernel/debug/hung_task
> cat semaphore & cat semaphore
and wait for hung_task message.
Signed-off-by: Lance Yang <ioworker0@...il.com>
Signed-off-by: Zi Li <amaindex@...look.com>
---
samples/Kconfig | 11 ++--
samples/hung_task/Makefile | 3 +-
samples/hung_task/hung_task_mutex.c | 20 ++++---
samples/hung_task/hung_task_semaphore.c | 74 +++++++++++++++++++++++++
4 files changed, 96 insertions(+), 12 deletions(-)
create mode 100644 samples/hung_task/hung_task_semaphore.c
diff --git a/samples/Kconfig b/samples/Kconfig
index 09011be2391a..3a073d6b848b 100644
--- a/samples/Kconfig
+++ b/samples/Kconfig
@@ -304,10 +304,13 @@ 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.
+ Build multiple modules to test the hung task detector. Each module
+ provides a simple debugfs file corresponding to a specific
+ synchronization primitive (e.g., mutex, semaphore, etc.). When the
+ file is read, the module will sleep for a long time (256 seconds)
+ while holding the respective synchronizer. If multiple processes
+ attempt to read these files concurrently, the hung_task watchdog
+ can detect potential hangs or deadlocks.
source "samples/rust/Kconfig"
diff --git a/samples/hung_task/Makefile b/samples/hung_task/Makefile
index fe9dde799880..7483c2c0a0ef 100644
--- a/samples/hung_task/Makefile
+++ b/samples/hung_task/Makefile
@@ -1,2 +1,3 @@
# SPDX-License-Identifier: GPL-2.0-only
-obj-$(CONFIG_SAMPLE_HUNG_TASK) += hung_task_mutex.o
\ No newline at end of file
+obj-$(CONFIG_SAMPLE_HUNG_TASK) += hung_task_mutex.o
+obj-$(CONFIG_SAMPLE_HUNG_TASK) += hung_task_semaphore.o
\ No newline at end of file
diff --git a/samples/hung_task/hung_task_mutex.c b/samples/hung_task/hung_task_mutex.c
index 7a29f2246d22..e4d1d69618b8 100644
--- a/samples/hung_task/hung_task_mutex.c
+++ b/samples/hung_task/hung_task_mutex.c
@@ -22,7 +22,7 @@
static const char dummy_string[] = "This is a dummy string.";
static DEFINE_MUTEX(dummy_mutex);
-struct dentry *hung_task_dir;
+static struct dentry *hung_task_dir;
static ssize_t read_dummy(struct file *file, char __user *user_buf,
size_t count, loff_t *ppos)
@@ -43,19 +43,25 @@ static const struct file_operations hung_task_fops = {
static int __init hung_task_sample_init(void)
{
- hung_task_dir = debugfs_create_dir(HUNG_TASK_DIR, NULL);
- if (IS_ERR(hung_task_dir))
- return PTR_ERR(hung_task_dir);
+ hung_task_dir = debugfs_lookup(HUNG_TASK_DIR, NULL);
+ if (!hung_task_dir) {
+ hung_task_dir = 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);
+ 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);
+ debugfs_lookup_and_remove(HUNG_TASK_FILE, hung_task_dir);
+
+ if (simple_empty(hung_task_dir))
+ debugfs_remove(hung_task_dir);
}
module_init(hung_task_sample_init);
diff --git a/samples/hung_task/hung_task_semaphore.c b/samples/hung_task/hung_task_semaphore.c
new file mode 100644
index 000000000000..a5814971bfb8
--- /dev/null
+++ b/samples/hung_task/hung_task_semaphore.c
@@ -0,0 +1,74 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * hung_task_semaphore.c - Sample code which causes hung task by semaphore
+ *
+ * Usage: load this module and read `<debugfs>/hung_task/semaphore`
+ * 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 <linux/debugfs.h>
+#include <linux/delay.h>
+#include <linux/fs.h>
+#include <linux/module.h>
+#include <linux/semaphore.h>
+
+#define HUNG_TASK_DIR "hung_task"
+#define HUNG_TASK_FILE "semaphore"
+#define SLEEP_SECOND 256
+
+static const char dummy_string[] = "This is a dummy string.";
+static DEFINE_SEMAPHORE(dummy_sem, 1);
+static 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 semaphore, it is uninterruptible sleep. */
+ down(&dummy_sem);
+
+ /* When the first task sleep here, it is interruptible. */
+ msleep_interruptible(SLEEP_SECOND * 1000);
+
+ up(&dummy_sem);
+
+ return simple_read_from_buffer(user_buf, count, ppos, dummy_string,
+ sizeof(dummy_string));
+}
+
+static const struct file_operations hung_task_fops = {
+ .read = read_dummy,
+};
+
+static int __init hung_task_sample_init(void)
+{
+ hung_task_dir = debugfs_lookup(HUNG_TASK_DIR, NULL);
+ if (!hung_task_dir) {
+ hung_task_dir = 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_lookup_and_remove(HUNG_TASK_FILE, hung_task_dir);
+
+ if (simple_empty(hung_task_dir))
+ debugfs_remove(hung_task_dir);
+}
+
+module_init(hung_task_sample_init);
+module_exit(hung_task_sample_exit);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Zi Li");
+MODULE_DESCRIPTION("Simple sleep under semaphore file for testing hung task");
--
2.45.2
Powered by blists - more mailing lists