linux-kernel - [tip:x86/fpu] x86/fpu: Don't reset thread.fpu

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Message-ID: <tip-a9241ea5fd709fc935dade130f4e3b2612bbe9e3@git.kernel.org>
Date:	Thu, 19 Feb 2015 03:32:24 -0800
From:	tip-bot for Oleg Nesterov <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	riel@...hat.com, torvalds@...ux-foundation.org, mingo@...nel.org,
	hpa@...or.com, oleg@...hat.com, tglx@...utronix.de, bp@...e.de,
	linux-kernel@...r.kernel.org
Subject: [tip:x86/fpu] x86/fpu: Don't reset thread.fpu_counter

Commit-ID:  a9241ea5fd709fc935dade130f4e3b2612bbe9e3
Gitweb:     http://git.kernel.org/tip/a9241ea5fd709fc935dade130f4e3b2612bbe9e3
Author:     Oleg Nesterov <oleg@...hat.com>
AuthorDate: Fri, 6 Feb 2015 15:01:58 -0500
Committer:  Borislav Petkov <bp@...e.de>
CommitDate: Thu, 19 Feb 2015 11:12:40 +0100

x86/fpu: Don't reset thread.fpu_counter

The "else" branch clears ->fpu_counter as a remnant of the lazy FPU
usage counting:

  e07e23e1fd30 ("[PATCH] non lazy "sleazy" fpu implementation")

However, switch_fpu_prepare() does this now so that else branch is
superfluous.

If we do use_eager_fpu(), then this has no effect. Otherwise, if we
actually wanted to prevent fpu preload after the context switch we would
need to reset it unconditionally, even if __thread_has_fpu().

Signed-off-by: Oleg Nesterov <oleg@...hat.com>
Signed-off-by: Rik van Riel <riel@...hat.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Link: http://lkml.kernel.org/r/1423252925-14451-2-git-send-email-riel@redhat.com
Signed-off-by: Borislav Petkov <bp@...e.de>
---
 arch/x86/kernel/i387.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/arch/x86/kernel/i387.c b/arch/x86/kernel/i387.c
index a9a4229..4d0db9e 100644
--- a/arch/x86/kernel/i387.c
+++ b/arch/x86/kernel/i387.c
@@ -108,8 +108,7 @@ void unlazy_fpu(struct task_struct *tsk)
 	if (__thread_has_fpu(tsk)) {
 		__save_init_fpu(tsk);
 		__thread_fpu_end(tsk);
-	} else
-		tsk->thread.fpu_counter = 0;
+	}
 	preempt_enable();
 }
 EXPORT_SYMBOL(unlazy_fpu);
--
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