Commit 9c37cb6e authored by Thomas Gleixner's avatar Thomas Gleixner Committed by Ingo Molnar
Browse files

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: default avatarPeter Zijlstra <peterz@infradead.org>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
Reviewed-by: default avatarMathieu Desnoyers <mathieu.desnoyers@efficios.com>
Link: https://patch.msgid.link/20251027084307.089270547@linutronix.de
parent 54129104

Documentation/admin-guide/kernel-parameters.txt

+4 −0
Original line number Diff line number Diff line
@@ -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: <bool>



	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.

include/linux/rseq_entry.h

+3 −0
Original line number Diff line number Diff line
@@ -34,6 +34,7 @@ DECLARE_PER_CPU(struct rseq_stats, rseq_stats); 
#endif /* !CONFIG_RSEQ_STATS */



#ifdef CONFIG_RSEQ

#include <linux/jump_label.h>

#include <linux/rseq.h>



#include <linux/tracepoint-defs.h>
@@ -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))

init/Kconfig

+14 −0
Original line number Diff line number Diff line
@@ -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.

kernel/rseq.c

+69 −4
Original line number Diff line number Diff line
@@ -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)