[tip:x86/urgent] x86, syscall: Fix _TIF_NOHZ handling in syscall_trace_enter_phase1

[tip-bot for Andy Lutomirski]

Commit-ID:  b5e212a3051b65e426a513901d9c7001681c7215
Gitweb:     http://git.kernel.org/tip/b5e212a3051b65e426a513901d9c7001681c7215
Author:     Andy Lutomirski <luto@xxxxxxxxxxxxxx>
AuthorDate: Wed, 19 Nov 2014 13:56:19 -0800
Committer:  Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitDate: Thu, 20 Nov 2014 23:01:53 +0100

x86, syscall: Fix _TIF_NOHZ handling in syscall_trace_enter_phase1

TIF_NOHZ is 19 (i.e. _TIF_SYSCALL_TRACE | _TIF_NOTIFY_RESUME |
_TIF_SINGLESTEP), not (1<<19).

This code is involved in Dave's trinity lockup, but I don't see why
it would cause any of the problems he's seeing, except inadvertently
by causing a different path through entry_64.S's syscall handling.

Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
Cc: Don Zickus <dzickus@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Dave Jones <davej@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/a6cd3b60a3f53afb6e1c8081b0ec30ff19003dd7.1416434075.git.luto@xxxxxxxxxxxxxx
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
---
 arch/x86/kernel/ptrace.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/ptrace.c b/arch/x86/kernel/ptrace.c
index 749b0e4..e510618 100644
--- a/arch/x86/kernel/ptrace.c
+++ b/arch/x86/kernel/ptrace.c
@@ -1484,7 +1484,7 @@ unsigned long syscall_trace_enter_phase1(struct pt_regs *regs, u32 arch)
 	 */
 	if (work & _TIF_NOHZ) {
 		user_exit();
-		work &= ~TIF_NOHZ;
+		work &= ~_TIF_NOHZ;
 	}
 
 #ifdef CONFIG_SECCOMP
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