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

[Thomas Gleixner <tglx@linutronix.de>]

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
 
 /*