linux-kernel - [PATCH 4.14 23/74] x86/mm: Remove superfluous barriers

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Date:   Wed, 27 Dec 2017 17:45:56 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andy Lutomirski <luto@...nel.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Borislav Petkov <bp@...en8.de>,
        Brian Gerst <brgerst@...il.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        David Laight <David.Laight@...lab.com>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        Eduardo Valentin <eduval@...zon.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Juergen Gross <jgross@...e.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Will Deacon <will.deacon@....com>, aliguori@...zon.com,
        daniel.gruss@...k.tugraz.at, hughd@...gle.com, keescook@...gle.com,
        linux-mm@...ck.org, Ingo Molnar <mingo@...nel.org>
Subject: [PATCH 4.14 23/74] x86/mm: Remove superfluous barriers

4.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Peter Zijlstra <peterz@...radead.org>

commit b5fc6d943808b570bdfbec80f40c6b3855f1c48b upstream.

atomic64_inc_return() already implies smp_mb() before and after.

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Boris Ostrovsky <boris.ostrovsky@...cle.com>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Brian Gerst <brgerst@...il.com>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: David Laight <David.Laight@...lab.com>
Cc: Denys Vlasenko <dvlasenk@...hat.com>
Cc: Eduardo Valentin <eduval@...zon.com>
Cc: Greg KH <gregkh@...uxfoundation.org>
Cc: H. Peter Anvin <hpa@...or.com>
Cc: Josh Poimboeuf <jpoimboe@...hat.com>
Cc: Juergen Gross <jgross@...e.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Will Deacon <will.deacon@....com>
Cc: aliguori@...zon.com
Cc: daniel.gruss@...k.tugraz.at
Cc: hughd@...gle.com
Cc: keescook@...gle.com
Cc: linux-mm@...ck.org
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 arch/x86/include/asm/tlbflush.h |    8 +-------
 1 file changed, 1 insertion(+), 7 deletions(-)

--- a/arch/x86/include/asm/tlbflush.h
+++ b/arch/x86/include/asm/tlbflush.h
@@ -60,19 +60,13 @@ static inline void invpcid_flush_all_non

 static inline u64 inc_mm_tlb_gen(struct mm_struct *mm)
 {
-	u64 new_tlb_gen;
-
 	/*
 	 * Bump the generation count.  This also serves as a full barrier
 	 * that synchronizes with switch_mm(): callers are required to order
 	 * their read of mm_cpumask after their writes to the paging
 	 * structures.
 	 */
-	smp_mb__before_atomic();
-	new_tlb_gen = atomic64_inc_return(&mm->context.tlb_gen);
-	smp_mb__after_atomic();
-
-	return new_tlb_gen;
+	return atomic64_inc_return(&mm->context.tlb_gen);
 }

 #ifdef CONFIG_PARAVIRT