From 9c37cb6e80b8fcdddc1236ba42ffd438f511192b Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Mon, 27 Oct 2025 09:44:55 +0100 Subject: [PATCH] rseq: Provide static branch for runtime debugging Config based debug is rarely turned on and is not available easily when things go wrong. Provide a static branch to allow permanent integration of debug mechanisms along with the usual toggles in Kconfig, command line and debugfs. Requested-by: Peter Zijlstra Signed-off-by: Thomas Gleixner Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Ingo Molnar Reviewed-by: Mathieu Desnoyers Link: https://patch.msgid.link/20251027084307.089270547@linutronix.de --- .../admin-guide/kernel-parameters.txt | 4 + include/linux/rseq_entry.h | 3 + init/Kconfig | 14 ++++ kernel/rseq.c | 73 ++++++++++++++++++- 4 files changed, 90 insertions(+), 4 deletions(-) diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index 6c42061ca20e5..e638274757927 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -6500,6 +6500,10 @@ Memory area to be used by remote processor image, managed by CMA. + rseq_debug= [KNL] Enable or disable restartable sequence + debug mode. Defaults to CONFIG_RSEQ_DEBUG_DEFAULT_ENABLE. + Format: + rt_group_sched= [KNL] Enable or disable SCHED_RR/FIFO group scheduling when CONFIG_RT_GROUP_SCHED=y. Defaults to !CONFIG_RT_GROUP_SCHED_DEFAULT_DISABLED. diff --git a/include/linux/rseq_entry.h b/include/linux/rseq_entry.h index ff9080b89be39..ed8e5f89499b3 100644 --- a/include/linux/rseq_entry.h +++ b/include/linux/rseq_entry.h @@ -34,6 +34,7 @@ DECLARE_PER_CPU(struct rseq_stats, rseq_stats); #endif /* !CONFIG_RSEQ_STATS */ #ifdef CONFIG_RSEQ +#include #include #include @@ -64,6 +65,8 @@ static inline void rseq_trace_ip_fixup(unsigned long ip, unsigned long start_ip, unsigned long offset, unsigned long abort_ip) { } #endif /* !CONFIG_TRACEPOINT */ +DECLARE_STATIC_KEY_MAYBE(CONFIG_RSEQ_DEBUG_DEFAULT_ENABLE, rseq_debug_enabled); + static __always_inline void rseq_note_user_irq_entry(void) { if (IS_ENABLED(CONFIG_GENERIC_IRQ_ENTRY)) diff --git a/init/Kconfig b/init/Kconfig index f39fdfb287978..bde40ab664e24 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -1925,10 +1925,24 @@ config RSEQ_STATS If unsure, say N. +config RSEQ_DEBUG_DEFAULT_ENABLE + default n + bool "Enable restartable sequences debug mode by default" if EXPERT + depends on RSEQ + help + This enables the static branch for debug mode of restartable + sequences. + + This also can be controlled on the kernel command line via the + command line parameter "rseq_debug=0/1" and through debugfs. + + If unsure, say N. + config DEBUG_RSEQ default n bool "Enable debugging of rseq() system call" if EXPERT depends on RSEQ && DEBUG_KERNEL + select RSEQ_DEBUG_DEFAULT_ENABLE help Enable extra debugging checks for the rseq system call. diff --git a/kernel/rseq.c b/kernel/rseq.c index c0dbe2ed26a89..679ab8ebdfd30 100644 --- a/kernel/rseq.c +++ b/kernel/rseq.c @@ -95,6 +95,27 @@ RSEQ_CS_FLAG_NO_RESTART_ON_SIGNAL | \ RSEQ_CS_FLAG_NO_RESTART_ON_MIGRATE) +DEFINE_STATIC_KEY_MAYBE(CONFIG_RSEQ_DEBUG_DEFAULT_ENABLE, rseq_debug_enabled); + +static inline void rseq_control_debug(bool on) +{ + if (on) + static_branch_enable(&rseq_debug_enabled); + else + static_branch_disable(&rseq_debug_enabled); +} + +static int __init rseq_setup_debug(char *str) +{ + bool on; + + if (kstrtobool(str, &on)) + return -EINVAL; + rseq_control_debug(on); + return 1; +} +__setup("rseq_debug=", rseq_setup_debug); + #ifdef CONFIG_TRACEPOINTS /* * Out of line, so the actual update functions can be in a header to be @@ -112,10 +133,11 @@ void __rseq_trace_ip_fixup(unsigned long ip, unsigned long start_ip, } #endif /* CONFIG_TRACEPOINTS */ +#ifdef CONFIG_DEBUG_FS #ifdef CONFIG_RSEQ_STATS DEFINE_PER_CPU(struct rseq_stats, rseq_stats); -static int rseq_debug_show(struct seq_file *m, void *p) +static int rseq_stats_show(struct seq_file *m, void *p) { struct rseq_stats stats = { }; unsigned int cpu; @@ -140,14 +162,56 @@ static int rseq_debug_show(struct seq_file *m, void *p) return 0; } +static int rseq_stats_open(struct inode *inode, struct file *file) +{ + return single_open(file, rseq_stats_show, inode->i_private); +} + +static const struct file_operations stat_ops = { + .open = rseq_stats_open, + .read = seq_read, + .llseek = seq_lseek, + .release = single_release, +}; + +static int __init rseq_stats_init(struct dentry *root_dir) +{ + debugfs_create_file("stats", 0444, root_dir, NULL, &stat_ops); + return 0; +} +#else +static inline void rseq_stats_init(struct dentry *root_dir) { } +#endif /* CONFIG_RSEQ_STATS */ + +static int rseq_debug_show(struct seq_file *m, void *p) +{ + bool on = static_branch_unlikely(&rseq_debug_enabled); + + seq_printf(m, "%d\n", on); + return 0; +} + +static ssize_t rseq_debug_write(struct file *file, const char __user *ubuf, + size_t count, loff_t *ppos) +{ + bool on; + + if (kstrtobool_from_user(ubuf, count, &on)) + return -EINVAL; + + rseq_control_debug(on); + return count; +} + static int rseq_debug_open(struct inode *inode, struct file *file) { return single_open(file, rseq_debug_show, inode->i_private); } -static const struct file_operations dfs_ops = { +static const struct file_operations debug_ops = { .open = rseq_debug_open, .read = seq_read, + .write = rseq_debug_write, .llseek = seq_lseek, .release = single_release, }; @@ -156,11 +220,12 @@ static int __init rseq_debugfs_init(void) { struct dentry *root_dir = debugfs_create_dir("rseq", NULL); - debugfs_create_file("stats", 0444, root_dir, NULL, &dfs_ops); + debugfs_create_file("debug", 0644, root_dir, NULL, &debug_ops); + rseq_stats_init(root_dir); return 0; } __initcall(rseq_debugfs_init); -#endif /* CONFIG_RSEQ_STATS */ +#endif /* CONFIG_DEBUG_FS */ #ifdef CONFIG_DEBUG_RSEQ static struct rseq *rseq_kernel_fields(struct task_struct *t) -- 2.47.3