linux-kernel - [PATCH 3/3] x86, fpu: kill save_init_fpu(), change math_error() to use unlazy

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Date:	Thu, 29 Jan 2015 22:08:37 +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 3/3] x86, fpu: kill save_init_fpu(), change math_error() to
	use unlazy_fpu()

math_error() calls save_init_fpu() after conditional_sti(), this means
that the caller can be preempted. If !use_eager_fpu() we can hit the
WARN_ON_ONCE(!__thread_has_fpu(tsk)) and/or save the wrong FPU state.

Change math_error() to use unlazy_fpu() and kill save_init_fpu().

Signed-off-by: Oleg Nesterov <oleg@...hat.com>
---
 arch/x86/include/asm/fpu-internal.h |   18 ------------------
 arch/x86/kernel/traps.c             |    2 +-
 2 files changed, 1 insertions(+), 19 deletions(-)

diff --git a/arch/x86/include/asm/fpu-internal.h b/arch/x86/include/asm/fpu-internal.h
index e97622f..02f2e08 100644
--- a/arch/x86/include/asm/fpu-internal.h
+++ b/arch/x86/include/asm/fpu-internal.h
@@ -518,24 +518,6 @@ static inline void __save_fpu(struct task_struct *tsk)
 }
 
 /*
- * These disable preemption on their own and are safe
- */
-static inline void save_init_fpu(struct task_struct *tsk)
-{
-	WARN_ON_ONCE(!__thread_has_fpu(tsk));
-
-	if (use_eager_fpu()) {
-		__save_fpu(tsk);
-		return;
-	}
-
-	preempt_disable();
-	__save_init_fpu(tsk);
-	__thread_fpu_end(tsk);
-	preempt_enable();
-}
-
-/*
  * i387 state interaction
  */
 static inline unsigned short get_fpu_cwd(struct task_struct *tsk)
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index fb4cb6a..51c4658 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -663,7 +663,7 @@ static void math_error(struct pt_regs *regs, int error_code, int trapnr)
 	/*
 	 * Save the info for the exception handler and clear the error.
 	 */
-	save_init_fpu(task);
+	unlazy_fpu(task);
 	task->thread.trap_nr = trapnr;
 	task->thread.error_code = error_code;
 	info.si_signo = SIGFPE;
-- 
1.5.5.1


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