linux-kernel - [PATCH 0/1] x86/cpu: don't allocate fpu->state for swapper/0

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Date:	Fri, 13 Mar 2015 19:26:56 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Dave Hansen <dave.hansen@...el.com>, Borislav Petkov <bp@...e.de>,
	Ingo Molnar <mingo@...nel.org>
Cc:	Andy Lutomirski <luto@...capital.net>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Pekka Riikonen <priikone@....fi>,
	Rik van Riel <riel@...hat.com>,
	Suresh Siddha <sbsiddha@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	"Yu, Fenghua" <fenghua.yu@...el.com>,
	Quentin Casasnovas <quentin.casasnovas@...cle.com>
Subject: [PATCH 0/1] x86/cpu: don't allocate fpu->state for swapper/0

Hello.

This patch is "out of order" a bit, but since Borislav mentioned this
during review...

And I was going to send the 2nd one (below), but it turns out that
__init_refok is not discarded? So is there any way to do

	void __init init_function();

	void non_init_func()
	{
		if (can_only_be_true_before_free_initmem)
			init_function();
	}

and avoid the warning?


Fenghua, could you please explain the SYSTEM_BOOTING check in __save_fpu?
It was added by f41d830fa8900 "x86/xsaves: Save xstate to task's xsave area
in __save_fpu during booting time", the changelog says:

	__save_fpu() can be called during early booting time

how? from where? Do we expect math_error()->unlazy_fpu() at boot time, or what?

Oleg.


--- a/arch/x86/kernel/xsave.c
+++ b/arch/x86/kernel/xsave.c
@@ -532,7 +532,7 @@ void setup_xstate_comp(void)
 /*
  * setup the xstate image representing the init state
  */
-static void __init setup_init_fpu_buf(void)
+static noinline void __init_refok setup_init_fpu_buf(void)
 {
 	/*
 	 * Setup init_xstate_buf to represent the init state of
@@ -677,16 +677,8 @@ void xsave_init(void)
 	this_func();
 }
 
-static inline void __init eager_fpu_init_bp(void)
-{
-	if (!init_xstate_buf)
-		setup_init_fpu_buf();
-}
-
 void eager_fpu_init(void)
 {
-	static __refdata void (*boot_func)(void) = eager_fpu_init_bp;
-
 	WARN_ON(used_math());
 	current_thread_info()->status = 0;
 
@@ -698,10 +690,8 @@ void eager_fpu_init(void)
 		return;
 	}
 
-	if (boot_func) {
-		boot_func();
-		boot_func = NULL;
-	}
+	if (!init_xstate_buf)
+		setup_init_fpu_buf();
 }
 
 /*

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