linux-kernel - [PATCH 1/3] x86, fpu: unlazy_fpu: don't reset thread.fpu

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Message-ID: <20150129210752.GB31584@redhat.com>
Date:	Thu, 29 Jan 2015 22:07:52 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Rik van Riel <riel@...hat.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>
Cc:	Suresh Siddha <sbsiddha@...il.com>,
	Andy Lutomirski <luto@...capital.net>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Fenghua Yu <fenghua.yu@...el.com>,
	the arch/x86 maintainers <x86@...nel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: [PATCH 1/3] x86, fpu: unlazy_fpu: don't reset thread.fpu_counter

It is not clear why the "else" branch clears ->fpu_counter, this makes
no sense.

If 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>
---
 arch/x86/kernel/i387.c |    3 +--
 1 files changed, 1 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/i387.c b/arch/x86/kernel/i387.c
index 4734865..c3b92c0 100644
--- a/arch/x86/kernel/i387.c
+++ b/arch/x86/kernel/i387.c
@@ -122,8 +122,7 @@ 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);
-- 
1.5.5.1


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