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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@linutronix.de>
AuthorDate: Wed, 23 Oct 2019 14:27:14 +02:00
Committer: Frederic Weisbecker <frederic@kernel.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@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Frederic Weisbecker <frederic@kernel.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 \
\
 
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