linux-kernel - [tip: timers/nohz] x86/entry: Remove _TIF_NOHZ from _TIF_WORK_SYSCALL

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Message-ID: <158281639829.28353.14112883202818177824.tip-bot2@tip-bot2>
Date:   Thu, 27 Feb 2020 15:13:18 -0000
From:   "tip-bot2 for Thomas Gleixner" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Borislav Petkov <bp@...en8.de>,
        Andy Lutomirski <luto@...nel.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        x86 <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>
Subject: [tip: timers/nohz] x86/entry: Remove _TIF_NOHZ from _TIF_WORK_SYSCALL_ENTRY

The following commit has been merged into the timers/nohz branch of tip:

Commit-ID:     7c805795307b40af50a45b7db44dd09ac1700947
Gitweb:        https://git.kernel.org/tip/7c805795307b40af50a45b7db44dd09ac1700947
Author:        Thomas Gleixner <tglx@...utronix.de>
AuthorDate:    Wed, 23 Oct 2019 14:27:14 +02:00
Committer:     Frederic Weisbecker <frederic@...nel.org>
CommitterDate: Fri, 14 Feb 2020 16:04:35 +01:00

x86/entry: Remove _TIF_NOHZ from _TIF_WORK_SYSCALL_ENTRY

Evaluating _TIF_NOHZ to decide whether to use the slow syscall entry path
is not only pointless, it's actually counterproductive:

 1) Context tracking code is invoked unconditionally before that flag is
    evaluated.

 2) If the flag is set the slow path is invoked for nothing due to #1

Remove it.

Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Andy Lutomirski <luto@...nel.org>
Signed-off-by: Frederic Weisbecker <frederic@...nel.org>
---
 arch/x86/include/asm/thread_info.h | 8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)

diff --git a/arch/x86/include/asm/thread_info.h b/arch/x86/include/asm/thread_info.h
index cf43279..6cb9d1b 100644
--- a/arch/x86/include/asm/thread_info.h
+++ b/arch/x86/include/asm/thread_info.h
@@ -133,14 +133,10 @@ struct thread_info {
 #define _TIF_X32		(1 << TIF_X32)
 #define _TIF_FSCHECK		(1 << TIF_FSCHECK)
 
-/*
- * work to do in syscall_trace_enter().  Also includes TIF_NOHZ for
- * enter_from_user_mode()
- */
+/* Work to do before invoking the actual syscall. */
 #define _TIF_WORK_SYSCALL_ENTRY	\
 	(_TIF_SYSCALL_TRACE | _TIF_SYSCALL_EMU | _TIF_SYSCALL_AUDIT |	\
-	 _TIF_SECCOMP | _TIF_SYSCALL_TRACEPOINT |	\
-	 _TIF_NOHZ)
+	 _TIF_SECCOMP | _TIF_SYSCALL_TRACEPOINT)
 
 /* flags to check in __switch_to() */
 #define _TIF_WORK_CTXSW_BASE					\