Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1734784

[PATCH -tip v3 5/7] kprobes/x86: Disable preempt ftrace-based jprobe

Show all headers | View raw

Disable preempt in ftrace-based jprobe handler as
described in Documentation/kprobes.txt, there is

"Probe handlers are run with preemption disabled."

This will fix jprobes behavior when CONFIG_PREEMPT=y.

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
---
 arch/x86/kernel/kprobes/ftrace.c |   23 ++++++++++++++---------
 1 file changed, 14 insertions(+), 9 deletions(-)

diff --git a/arch/x86/kernel/kprobes/ftrace.c b/arch/x86/kernel/kprobes/ftrace.c
index 041f7b6dfa0f..bcfee4f69b0e 100644
--- a/arch/x86/kernel/kprobes/ftrace.c
+++ b/arch/x86/kernel/kprobes/ftrace.c
@@ -26,7 +26,7 @@
 #include "common.h"
 
 static nokprobe_inline
-int __skip_singlestep(struct kprobe *p, struct pt_regs *regs,
+void __skip_singlestep(struct kprobe *p, struct pt_regs *regs,
 		      struct kprobe_ctlblk *kcb, unsigned long orig_ip)
 {
 	/*
@@ -41,20 +41,21 @@ int __skip_singlestep(struct kprobe *p, struct pt_regs *regs,
 	__this_cpu_write(current_kprobe, NULL);
 	if (orig_ip)
 		regs->ip = orig_ip;
-	return 1;
 }
 
 int skip_singlestep(struct kprobe *p, struct pt_regs *regs,
 		    struct kprobe_ctlblk *kcb)
 {
-	if (kprobe_ftrace(p))
-		return __skip_singlestep(p, regs, kcb, 0);
-	else
-		return 0;
+	if (kprobe_ftrace(p)) {
+		__skip_singlestep(p, regs, kcb, 0);
+		preempt_enable_no_resched();
+		return 1;
+	}
+	return 0;
 }
 NOKPROBE_SYMBOL(skip_singlestep);
 
-/* Ftrace callback handler for kprobes */
+/* Ftrace callback handler for kprobes -- called under preepmt disabed */
 void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip,
 			   struct ftrace_ops *ops, struct pt_regs *regs)
 {
@@ -77,13 +78,17 @@ void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip,
 		/* Kprobe handler expects regs->ip = ip + 1 as breakpoint hit */
 		regs->ip = ip + sizeof(kprobe_opcode_t);
 
+		/* To emulate trap based kprobes, preempt_disable here */
+		preempt_disable();
 		__this_cpu_write(current_kprobe, p);
 		kcb->kprobe_status = KPROBE_HIT_ACTIVE;
-		if (!p->pre_handler || !p->pre_handler(p, regs))
+		if (!p->pre_handler || !p->pre_handler(p, regs)) {
 			__skip_singlestep(p, regs, kcb, orig_ip);
+			preempt_enable_no_resched();
+		}
 		/*
 		 * If pre_handler returns !0, it sets regs->ip and
-		 * resets current kprobe.
+		 * resets current kprobe, and keep preempt count +1.
 		 */
 	}
 end:

Back to linux.kernel | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

[PATCH -tip v3 0/7] kprobes/x86: Preempt related enhancements Masami Hiramatsu <mhiramat@kernel.org> - 2017-09-19 12:00 +0200
  [PATCH -tip v3 1/7] kprobes: Improve smoke test to check preemptible Masami Hiramatsu <mhiramat@kernel.org> - 2017-09-19 12:00 +0200
  [PATCH -tip v3 7/7] kprobes: Use synchronize_rcu_tasks() for optprobe with CONFIG_PREEMPT Masami Hiramatsu <mhiramat@kernel.org> - 2017-09-19 12:10 +0200
  [PATCH -tip v3 3/7] kprobes: Warn if optprobe handler tries to change execution path Masami Hiramatsu <mhiramat@kernel.org> - 2017-09-19 12:10 +0200
  [PATCH -tip v3 5/7] kprobes/x86: Disable preempt ftrace-based jprobe Masami Hiramatsu <mhiramat@kernel.org> - 2017-09-19 12:10 +0200
  [PATCH -tip v3 4/7] kprobes/x86: Disable preempt in optprobe Masami Hiramatsu <mhiramat@kernel.org> - 2017-09-19 12:10 +0200
  [PATCH -tip v3 2/7] kprobes/x86: Move get_kprobe_ctlblk in irq-disabled block Masami Hiramatsu <mhiramat@kernel.org> - 2017-09-19 12:10 +0200
  [PATCH -tip v3 6/7] kprobes/x86: Remove disable_irq from ftrace-based/optimized kprobe Masami Hiramatsu <mhiramat@kernel.org> - 2017-09-19 12:10 +0200

csiph-web