[patch V4 22/36] rseq: Use static branch for syscall exit debug when GENERIC_IRQ_ENTRY=y

Thomas Gleixner
2025-09-08T21:32:13Z

Make the syscall exit debug mechanism available via the static branch on
architectures which utilize the generic entry code.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

---
include/linux/entry-common.h | 2 +-
include/linux/rseq_entry.h | 9 +++++++++
kernel/rseq.c | 19 +++++++++++++------
3 files changed, 23 insertions(+), 7 deletions(-)

--- a/include/linux/entry-common.h
+++ b/include/linux/entry-common.h
@@ -146,7 +146,7 @@ static __always_inline void syscall_exit
local_irq_enable();
}

- rseq_syscall(regs);
+ rseq_debug_syscall_return(regs);

/*
* Do one-time syscall specific work. If these work items are
--- a/include/linux/rseq_entry.h
+++ b/include/linux/rseq_entry.h
@@ -286,9 +286,18 @@ static __always_inline void rseq_exit_to
ev->events = 0;
}

+void __rseq_debug_syscall_return(struct pt_regs *regs);
+
+static inline void rseq_debug_syscall_return(struct pt_regs *regs)
+{
+ if (static_branch_unlikely(&rseq_debug_enabled))
+ __rseq_debug_syscall_return(regs);
+}
+
#else /* CONFIG_RSEQ */
static inline void rseq_note_user_irq_entry(void) { }
static inline void rseq_exit_to_user_mode(void) { }
+static inline void rseq_debug_syscall_return(struct pt_regs *regs) { }
#endif /* !CONFIG_RSEQ */

#endif /* _LINUX_RSEQ_ENTRY_H */
--- a/kernel/rseq.c
+++ b/kernel/rseq.c
@@ -470,12 +470,7 @@ void __rseq_handle_notify_resume(struct
force_sigsegv(sig);
}

-#ifdef CONFIG_DEBUG_RSEQ
-/*
- * Terminate the process if a syscall is issued within a restartable
- * sequence.
- */
-void rseq_syscall(struct pt_regs *regs)
+void __rseq_debug_syscall_return(struct pt_regs *regs)
{
struct task_struct *t = current;
u64 csaddr;
@@ -493,6 +488,18 @@ void rseq_syscall(struct pt_regs *regs)
fail:
force_sig(SIGSEGV);
}
+
+#ifdef CONFIG_DEBUG_RSEQ
+/*
+ * Kept around to keep GENERIC_ENTRY=n architectures supported.
+ *
+ * Terminate the process if a syscall is issued within a restartable
+ * sequence.
+ */
+void rseq_syscall(struct pt_regs *regs)
+{
+ __rseq_debug_syscall_return(regs);
+}
#endif

/*