From 6668ed271eaefaa63e686bdfbedaeb7b8e492722 Mon Sep 17 00:00:00 2001 From: Kumar Kartikeya Dwivedi Date: Fri, 4 Sep 2026 10:43:19 +0200 Subject: selftests/bpf: Reject graph kptr use after RCU unlock Add a sleepable verifier test that loads a graph-node local kptr in an explicit RCU read-side critical section, then passes its node to bpf_rbtree_remove() after the section ends. Before the verifier fix, the stale NON_OWN_REF flag makes the node look like a live borrowed reference and the program is accepted. After the fix, the pointer is demoted without NON_OWN_REF and the graph kfunc argument is rejected. Also exercise a graph kptr loaded while a spin lock provides implicit RCU protection. The pointer must be invalidated when the lock is released, which guards the required ordering between non-owning-reference invalidation and RCU demotion. Update the existing fault-protected load test state description. The post-unlock pointer no longer carries NON_OWN_REF, but remains readable because the load is rewritten to use BPF_PROBE_MEM. Signed-off-by: Kumar Kartikeya Dwivedi Link: https://lore.kernel.org/r/20260904084325.52250-7-memxor@gmail.com Signed-off-by: Alexei Starovoitov --- samples/hung_task/Makefile | 2 + samples/hung_task/hung_task_tests.c | 164 ++++++++++++++++++++++++++++++++++++ 2 files changed, 166 insertions(+) create mode 100644 samples/hung_task/Makefile create mode 100644 samples/hung_task/hung_task_tests.c (limited to 'samples/hung_task') diff --git a/samples/hung_task/Makefile b/samples/hung_task/Makefile new file mode 100644 index 000000000..86036f1a2 --- /dev/null +++ b/samples/hung_task/Makefile @@ -0,0 +1,2 @@ +# SPDX-License-Identifier: GPL-2.0-only +obj-$(CONFIG_SAMPLE_HUNG_TASK) += hung_task_tests.o diff --git a/samples/hung_task/hung_task_tests.c b/samples/hung_task/hung_task_tests.c new file mode 100644 index 000000000..0360ec916 --- /dev/null +++ b/samples/hung_task/hung_task_tests.c @@ -0,0 +1,164 @@ +// SPDX-License-Identifier: GPL-2.0-or-later +/* + * hung_task_tests.c - Sample code for testing hung tasks with mutex, + * semaphore, etc. + * + * Usage: Load this module and read `/hung_task/mutex`, + * `/hung_task/semaphore`, `/hung_task/rw_semaphore_read`, + * `/hung_task/rw_semaphore_write`, etc., with 2 or more processes. + * + * This is for testing kernel hung_task error messages with various locking + * mechanisms (e.g., mutex, semaphore, rw_semaphore_read, rw_semaphore_write, etc.). + * Note that this may freeze your system or cause a panic. Use only for testing purposes. + */ + +#include +#include +#include +#include +#include +#include +#include + +#define HUNG_TASK_DIR "hung_task" +#define HUNG_TASK_MUTEX_FILE "mutex" +#define HUNG_TASK_SEM_FILE "semaphore" +#define HUNG_TASK_RWSEM_READ_FILE "rw_semaphore_read" +#define HUNG_TASK_RWSEM_WRITE_FILE "rw_semaphore_write" +#define SLEEP_SECOND 256 + +static const char dummy_string[] = "This is a dummy string."; +static DEFINE_MUTEX(dummy_mutex); +static DEFINE_SEMAPHORE(dummy_sem, 1); +static DECLARE_RWSEM(dummy_rwsem); +static struct dentry *hung_task_dir; + +/* Mutex-based read function */ +static ssize_t read_dummy_mutex(struct file *file, char __user *user_buf, + size_t count, loff_t *ppos) +{ + /* Check if data is already read */ + if (*ppos >= sizeof(dummy_string)) + return 0; + + /* Second task waits on mutex, entering uninterruptible sleep */ + guard(mutex)(&dummy_mutex); + + /* First task sleeps here, interruptible */ + msleep_interruptible(SLEEP_SECOND * 1000); + + return simple_read_from_buffer(user_buf, count, ppos, dummy_string, + sizeof(dummy_string)); +} + +/* Semaphore-based read function */ +static ssize_t read_dummy_semaphore(struct file *file, char __user *user_buf, + size_t count, loff_t *ppos) +{ + /* Check if data is already read */ + if (*ppos >= sizeof(dummy_string)) + return 0; + + /* Second task waits on semaphore, entering uninterruptible sleep */ + down(&dummy_sem); + + /* First task sleeps here, interruptible */ + msleep_interruptible(SLEEP_SECOND * 1000); + + up(&dummy_sem); + + return simple_read_from_buffer(user_buf, count, ppos, dummy_string, + sizeof(dummy_string)); +} + +/* Read-write semaphore read function */ +static ssize_t read_dummy_rwsem_read(struct file *file, char __user *user_buf, + size_t count, loff_t *ppos) +{ + /* Check if data is already read */ + if (*ppos >= sizeof(dummy_string)) + return 0; + + /* Acquires read lock, allowing concurrent readers but blocks if write lock is held */ + down_read(&dummy_rwsem); + + /* Sleeps here, potentially triggering hung task detection if lock is held too long */ + msleep_interruptible(SLEEP_SECOND * 1000); + + up_read(&dummy_rwsem); + + return simple_read_from_buffer(user_buf, count, ppos, dummy_string, + sizeof(dummy_string)); +} + +/* Read-write semaphore write function */ +static ssize_t read_dummy_rwsem_write(struct file *file, char __user *user_buf, + size_t count, loff_t *ppos) +{ + /* Check if data is already read */ + if (*ppos >= sizeof(dummy_string)) + return 0; + + /* Acquires exclusive write lock, blocking all other readers and writers */ + down_write(&dummy_rwsem); + + /* Sleeps here, potentially triggering hung task detection if lock is held too long */ + msleep_interruptible(SLEEP_SECOND * 1000); + + up_write(&dummy_rwsem); + + return simple_read_from_buffer(user_buf, count, ppos, dummy_string, + sizeof(dummy_string)); +} + +/* File operations for mutex */ +static const struct file_operations hung_task_mutex_fops = { + .read = read_dummy_mutex, +}; + +/* File operations for semaphore */ +static const struct file_operations hung_task_sem_fops = { + .read = read_dummy_semaphore, +}; + +/* File operations for rw_semaphore read */ +static const struct file_operations hung_task_rwsem_read_fops = { + .read = read_dummy_rwsem_read, +}; + +/* File operations for rw_semaphore write */ +static const struct file_operations hung_task_rwsem_write_fops = { + .read = read_dummy_rwsem_write, +}; + +static int __init hung_task_tests_init(void) +{ + hung_task_dir = debugfs_create_dir(HUNG_TASK_DIR, NULL); + if (IS_ERR(hung_task_dir)) + return PTR_ERR(hung_task_dir); + + /* Create debugfs files for mutex and semaphore tests */ + debugfs_create_file(HUNG_TASK_MUTEX_FILE, 0400, hung_task_dir, NULL, + &hung_task_mutex_fops); + debugfs_create_file(HUNG_TASK_SEM_FILE, 0400, hung_task_dir, NULL, + &hung_task_sem_fops); + debugfs_create_file(HUNG_TASK_RWSEM_READ_FILE, 0400, hung_task_dir, NULL, + &hung_task_rwsem_read_fops); + debugfs_create_file(HUNG_TASK_RWSEM_WRITE_FILE, 0400, hung_task_dir, NULL, + &hung_task_rwsem_write_fops); + + return 0; +} + +static void __exit hung_task_tests_exit(void) +{ + debugfs_remove_recursive(hung_task_dir); +} + +module_init(hung_task_tests_init); +module_exit(hung_task_tests_exit); + +MODULE_LICENSE("GPL"); +MODULE_AUTHOR("Masami Hiramatsu "); +MODULE_AUTHOR("Zi Li "); +MODULE_DESCRIPTION("Simple sleep under lock files for testing hung task"); -- cgit v1.3.1