[tip:perf/core] x86/signals: Clear RF EFLAGS bit for signal handler

[tip-bot for Jiri Olsa <tipbot@zytor.com>]

Commit-ID:  24cda10996f5420ab962f91cd03c15869a3a94b1
Gitweb:     http://git.kernel.org/tip/24cda10996f5420ab962f91cd03c15869a3a94b1
Author:     Jiri Olsa <jolsa@redhat.com>
AuthorDate: Wed, 1 May 2013 17:25:42 +0200
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Tue, 28 May 2013 08:46:52 +0200

x86/signals: Clear RF EFLAGS bit for signal handler

Clearing RF EFLAGS bit for signal handler. The reason is
that this flag is set by debug exception code to prevent
the recursive exception entry.

Leaving it set for signal handler might prevent debug
exception of the signal handler itself.

Signed-off-by: Jiri Olsa <jolsa@redhat.com>
Tested-by: Oleg Nesterov <oleg@redhat.com>
Reviewed-by: Frederic Weisbecker <fweisbec@gmail.com>
Originally-Reported-by: Vince Weaver <vincent.weaver@maine.edu>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Cc: Stephane Eranian <eranian@google.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1367421944-19082-3-git-send-email-jolsa@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 arch/x86/kernel/signal.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/arch/x86/kernel/signal.c b/arch/x86/kernel/signal.c
index 9df4c0b..cb12fc9 100644
--- a/arch/x86/kernel/signal.c
+++ b/arch/x86/kernel/signal.c
@@ -665,6 +665,12 @@ handle_signal(struct ksignal *ksig, struct pt_regs *regs)
 		 */
 		regs->flags &= ~X86_EFLAGS_DF;
 		/*
+		 * Clear RF when entering the signal handler, because
+		 * it might disable possible debug exception from the
+		 * signal handler.
+		 */
+		regs->flags &= ~X86_EFLAGS_RF;
+		/*
 		 * Clear TF when entering the signal handler, but
 		 * notify any tracer that was single-stepping it.
 		 * The tracer may want to single-step inside the