On Sat, Dec 25, 2004 at 04:24:30AM +0100, Andrea Arcangeli wrote:
> Here it is the first part. This makes memdie a TIF_MEMDIE. It's

And here is the final incremental part converting ->used_math to
PF_USED_MATH.

All combined patches work for me. I'm not going to apply these last two
(5/4 and 6/4) to the stable suse tree though, I'll apply 5/4 and 6/4
only to the future ones based on 2.6.10+, since the ev4 race on
SMP/PREEMPT is not relevant for the suse tree (those last two patches
are a bit too big to take any risk for a _purerly_theoretical_ race on
ev4 + SMP or ev4 + PREEMPT ;). The PF_MEMDIE was instead a more pratical
race (Wli said he triggered it in practice too) and it was triggering on
all archs, not just on ev4 + SMP or evr + PREEMPT, that's fixed with
[1-4]/4.

The below headers are from the SUSE patch format. I attached the script
I use to generate those just in case somebody can find it useful. It's
quite generic and it avoids to destroy the patch headers every time. If
you use quilt probably you don't need it. mkpatch.py works pretty fast
in combination with patch -p1 -b or alternatively in combination with
emacs autofile save.

Merry Christmas and Happy new Year to everyone, I'll be on vacations
until 2 Jan, so if there's any problem with this stuff we'll talk about
it next year ;). I just attempted to finish it before leaving.

From: Andrea Arcangeli <andrea@suse.de>
Subject: Convert the unsafe signed (16bit) used_math to a safe and optimal PF_USED_MATH

... and declare oomkilladj as an int since it can be changed via /proc.

I might have broken arm, see the very first change in the patch to
asm-offsets.c, rest looks ok at first glance.

If you want used_math to return 0 or 1 (instead of 0 or PF_USED_MATH),
just s/!!// in the below patch and place !! in sched.h::*used_math()
accordingly after applying the patch, it should work just fine. Using !!
only when necessary as the below is optimal.

Signed-off-by: Andrea Arcangeli <andrea@suse.de>

--- x/arch/arm26/kernel/asm-offsets.c.~1~	2003-07-17 01:52:38.000000000 +0200
+++ x/arch/arm26/kernel/asm-offsets.c	2004-12-25 15:18:54.589979544 +0100
@@ -42,7 +42,6 @@
 
 int main(void)
 {
-  DEFINE(TSK_USED_MATH,		offsetof(struct task_struct, used_math));
   DEFINE(TSK_ACTIVE_MM,		offsetof(struct task_struct, active_mm));
   BLANK();
   DEFINE(VMA_VM_MM,		offsetof(struct vm_area_struct, vm_mm));
--- x/arch/arm26/kernel/process.c.~1~	2004-08-25 02:47:33.000000000 +0200
+++ x/arch/arm26/kernel/process.c	2004-12-25 15:18:54.591979240 +0100
@@ -296,7 +296,7 @@ void flush_thread(void)
 	memset(&tsk->thread.debug, 0, sizeof(struct debug_info));
 	memset(&thread->fpstate, 0, sizeof(union fp_state));
 
-	current->used_math = 0;
+	clear_used_math();
 }
 
 void release_thread(struct task_struct *dead_task)
@@ -330,7 +330,7 @@ copy_thread(int nr, unsigned long clone_
 int dump_fpu (struct pt_regs *regs, struct user_fp *fp)
 {
 	struct thread_info *thread = current_thread_info();
-	int used_math = current->used_math;
+	int used_math = !!used_math();
 
 	if (used_math)
 		memcpy(fp, &thread->fpstate.soft, sizeof (*fp));
--- x/arch/arm26/kernel/ptrace.c.~1~	2004-12-04 08:56:19.000000000 +0100
+++ x/arch/arm26/kernel/ptrace.c	2004-12-25 15:18:54.592979088 +0100
@@ -540,7 +540,7 @@ static int ptrace_getfpregs(struct task_
  */
 static int ptrace_setfpregs(struct task_struct *tsk, void *ufp)
 {
-	tsk->used_math = 1;
+	set_stopped_child_used_math(tsk);
 	return copy_from_user(&tsk->thread_info->fpstate, ufp,
 			      sizeof(struct user_fp)) ? -EFAULT : 0;
 }
--- x/arch/i386/kernel/cpu/common.c.~1~	2004-12-04 08:54:53.000000000 +0100
+++ x/arch/i386/kernel/cpu/common.c	2004-12-25 15:18:54.593978936 +0100
@@ -580,6 +580,6 @@ void __init cpu_init (void)
 	 * Force FPU initialization:
 	 */
 	current_thread_info()->status = 0;
-	current->used_math = 0;
+	clear_used_math();
 	mxcsr_feature_mask_init();
 }
--- x/arch/i386/kernel/i387.c.~1~	2004-12-04 08:56:19.000000000 +0100
+++ x/arch/i386/kernel/i387.c	2004-12-25 15:18:54.594978784 +0100
@@ -60,7 +60,8 @@ void init_fpu(struct task_struct *tsk)
 		tsk->thread.i387.fsave.twd = 0xffffffffu;
 		tsk->thread.i387.fsave.fos = 0xffff0000u;
 	}
-	tsk->used_math = 1;
+	/* only the device not available exception or ptrace can call init_fpu */
+	set_stopped_child_used_math(tsk);
 }
 
 /*
@@ -330,13 +331,13 @@ static int save_i387_fxsave( struct _fps
 
 int save_i387( struct _fpstate __user *buf )
 {
-	if ( !current->used_math )
+	if ( !used_math() )
 		return 0;
 
 	/* This will cause a "finit" to be triggered by the next
 	 * attempted FPU operation by the 'current' process.
 	 */
-	current->used_math = 0;
+	clear_used_math();
 
 	if ( HAVE_HWFP ) {
 		if ( cpu_has_fxsr ) {
@@ -382,7 +383,7 @@ int restore_i387( struct _fpstate __user
 	} else {
 		err = restore_i387_soft( &current->thread.i387.soft, buf );
 	}
-	current->used_math = 1;
+	set_used_math();
 	return err;
 }
 
@@ -506,7 +507,7 @@ int dump_fpu( struct pt_regs *regs, stru
 	int fpvalid;
 	struct task_struct *tsk = current;
 
-	fpvalid = tsk->used_math;
+	fpvalid = !!used_math();
 	if ( fpvalid ) {
 		unlazy_fpu( tsk );
 		if ( cpu_has_fxsr ) {
@@ -521,7 +522,7 @@ int dump_fpu( struct pt_regs *regs, stru
 
 int dump_task_fpu(struct task_struct *tsk, struct user_i387_struct *fpu)
 {
-	int fpvalid = tsk->used_math;
+	int fpvalid = !!tsk_used_math(tsk);
 
 	if (fpvalid) {
 		if (tsk == current)
@@ -536,7 +537,7 @@ int dump_task_fpu(struct task_struct *ts
 
 int dump_task_extended_fpu(struct task_struct *tsk, struct user_fxsr_struct *fpu)
 {
-	int fpvalid = tsk->used_math && cpu_has_fxsr;
+	int fpvalid = tsk_used_math(tsk) && cpu_has_fxsr;
 
 	if (fpvalid) {
 		if (tsk == current)
--- x/arch/i386/kernel/process.c.~1~	2004-12-04 08:56:19.000000000 +0100
+++ x/arch/i386/kernel/process.c	2004-12-25 15:18:54.596978480 +0100
@@ -333,7 +333,7 @@ void flush_thread(void)
 	 * Forget coprocessor state..
 	 */
 	clear_fpu(tsk);
-	tsk->used_math = 0;
+	clear_used_math();
 }
 
 void release_thread(struct task_struct *dead_task)
--- x/arch/i386/kernel/ptrace.c.~1~	2004-12-04 08:56:19.000000000 +0100
+++ x/arch/i386/kernel/ptrace.c	2004-12-25 15:18:54.597978328 +0100
@@ -491,7 +491,7 @@ asmlinkage int sys_ptrace(long request, 
 			break;
 		}
 		ret = 0;
-		if (!child->used_math)
+		if (!tsk_used_math(child))
 			init_fpu(child);
 		get_fpregs((struct user_i387_struct __user *)data, child);
 		break;
@@ -503,7 +503,7 @@ asmlinkage int sys_ptrace(long request, 
 			ret = -EIO;
 			break;
 		}
-		child->used_math = 1;
+		set_stopped_child_used_math(child);
 		set_fpregs(child, (struct user_i387_struct __user *)data);
 		ret = 0;
 		break;
@@ -515,7 +515,7 @@ asmlinkage int sys_ptrace(long request, 
 			ret = -EIO;
 			break;
 		}
-		if (!child->used_math)
+		if (!tsk_used_math(child))
 			init_fpu(child);
 		ret = get_fpxregs((struct user_fxsr_struct __user *)data, child);
 		break;
@@ -527,7 +527,7 @@ asmlinkage int sys_ptrace(long request, 
 			ret = -EIO;
 			break;
 		}
-		child->used_math = 1;
+		set_stopped_child_used_math(child);
 		ret = set_fpxregs(child, (struct user_fxsr_struct __user *)data);
 		break;
 	}
--- x/arch/i386/kernel/traps.c.~1~	2004-12-04 08:56:19.000000000 +0100
+++ x/arch/i386/kernel/traps.c	2004-12-25 15:18:54.598978176 +0100
@@ -920,7 +920,7 @@ asmlinkage void math_state_restore(struc
 	struct task_struct *tsk = thread->task;
 
 	clts();		/* Allow maths ops (or we recurse) */
-	if (!tsk->used_math)
+	if (!tsk_used_math(tsk))
 		init_fpu(tsk);
 	restore_fpu(tsk);
 	thread->status |= TS_USEDFPU;	/* So we fnsave on switch_to() */
--- x/arch/i386/math-emu/fpu_entry.c.~1~	2004-08-25 02:47:49.000000000 +0200
+++ x/arch/i386/math-emu/fpu_entry.c	2004-12-25 15:18:54.599978024 +0100
@@ -155,10 +155,10 @@ asmlinkage void math_emulate(long arg)
   RE_ENTRANT_CHECK_ON;
 #endif /* RE_ENTRANT_CHECKING */
 
-  if (!current->used_math)
+  if (!used_math())
     {
       finit();
-      current->used_math = 1;
+      set_used_math();
     }
 
   SETUP_DATA_AREA(arg);
--- x/arch/ia64/ia32/elfcore32.h.~1~	2004-12-04 08:56:19.000000000 +0100
+++ x/arch/ia64/ia32/elfcore32.h	2004-12-25 15:18:54.600977872 +0100
@@ -106,7 +106,7 @@ elf_core_copy_task_fpregs(struct task_st
 	struct ia32_user_i387_struct *fpstate = (void*)fpu;
 	mm_segment_t old_fs;
 
-	if (!tsk->used_math)
+	if (!tsk_used_math(tsk))
 		return 0;
 	
 	old_fs = get_fs();
@@ -124,7 +124,7 @@ elf_core_copy_task_xfpregs(struct task_s
 	struct ia32_user_fxsr_struct *fpxstate = (void*) xfpu;
 	mm_segment_t old_fs;
 
-	if (!tsk->used_math)
+	if (!tsk_used_math(tsk))
 		return 0;
 
 	old_fs = get_fs();
--- x/arch/mips/kernel/irixsig.c.~1~	2004-12-04 08:56:20.000000000 +0100
+++ x/arch/mips/kernel/irixsig.c	2004-12-25 15:18:54.601977720 +0100
@@ -100,7 +100,7 @@ static void setup_irix_frame(struct k_si
 	__put_user((u64) regs->hi, &ctx->hi);
 	__put_user((u64) regs->lo, &ctx->lo);
 	__put_user((u64) regs->cp0_epc, &ctx->pc);
-	__put_user(current->used_math, &ctx->usedfp);
+	__put_user(!!used_math(), &ctx->usedfp);
 	__put_user((u64) regs->cp0_cause, &ctx->cp0_cause);
 	__put_user((u64) regs->cp0_badvaddr, &ctx->cp0_badvaddr);
 
@@ -728,7 +728,7 @@ asmlinkage int irix_getcontext(struct pt
 	__put_user(regs->cp0_epc, &ctx->regs[35]);
 
 	flags = 0x0f;
-	if(!current->used_math) {
+	if(!used_math()) {
 		flags &= ~(0x08);
 	} else {
 		/* XXX wheee... */
--- x/arch/mips/kernel/process.c.~1~	2004-12-04 08:56:20.000000000 +0100
+++ x/arch/mips/kernel/process.c	2004-12-25 15:18:54.602977568 +0100
@@ -76,7 +76,7 @@ void start_thread(struct pt_regs * regs,
 #endif
 	status |= KU_USER;
 	regs->cp0_status = status;
-	current->used_math = 0;
+	clear_used_math();
 	lose_fpu();
 	regs->cp0_epc = pc;
 	regs->regs[29] = sp;
--- x/arch/mips/kernel/ptrace.c.~1~	2004-12-04 08:56:20.000000000 +0100
+++ x/arch/mips/kernel/ptrace.c	2004-12-25 15:18:54.603977416 +0100
@@ -119,7 +119,7 @@ asmlinkage int sys_ptrace(long request, 
 			tmp = regs->regs[addr];
 			break;
 		case FPR_BASE ... FPR_BASE + 31:
-			if (child->used_math) {
+			if (tsk_used_math(child)) {
 				fpureg_t *fregs = get_fpu_regs(child);
 
 #ifdef CONFIG_MIPS32
@@ -205,7 +205,7 @@ asmlinkage int sys_ptrace(long request, 
 		case FPR_BASE ... FPR_BASE + 31: {
 			fpureg_t *fregs = get_fpu_regs(child);
 
-			if (!child->used_math) {
+			if (!tsk_used_math(child)) {
 				/* FP not yet used  */
 				memset(&child->thread.fpu.hard, ~0,
 				       sizeof(child->thread.fpu.hard));
--- x/arch/mips/kernel/ptrace32.c.~1~	2004-12-04 08:56:20.000000000 +0100
+++ x/arch/mips/kernel/ptrace32.c	2004-12-25 15:18:54.604977264 +0100
@@ -112,7 +112,7 @@ asmlinkage int sys32_ptrace(int request,
 			tmp = regs->regs[addr];
 			break;
 		case FPR_BASE ... FPR_BASE + 31:
-			if (child->used_math) {
+			if (tsk_used_math(child)) {
 				fpureg_t *fregs = get_fpu_regs(child);
 
 				/*
@@ -193,7 +193,7 @@ asmlinkage int sys32_ptrace(int request,
 		case FPR_BASE ... FPR_BASE + 31: {
 			fpureg_t *fregs = get_fpu_regs(child);
 
-			if (!child->used_math) {
+			if (!tsk_used_math(child)) {
 				/* FP not yet used  */
 				memset(&child->thread.fpu.hard, ~0,
 				       sizeof(child->thread.fpu.hard));
--- x/arch/mips/kernel/signal.c.~1~	2004-12-04 08:56:20.000000000 +0100
+++ x/arch/mips/kernel/signal.c	2004-12-25 15:18:54.605977112 +0100
@@ -179,11 +179,11 @@ asmlinkage int restore_sigcontext(struct
 	restore_gp_reg(31);
 #undef restore_gp_reg
 
-	err |= __get_user(current->used_math, &sc->sc_used_math);
+	err |= __get_user(!!used_math(), &sc->sc_used_math);
 
 	preempt_disable();
 
-	if (current->used_math) {
+	if (used_math()) {
 		/* restore fpu context if we have used it before */
 		own_fpu();
 		err |= restore_fp_context(sc);
@@ -324,9 +324,9 @@ inline int setup_sigcontext(struct pt_re
 	err |= __put_user(regs->cp0_cause, &sc->sc_cause);
 	err |= __put_user(regs->cp0_badvaddr, &sc->sc_badvaddr);
 
-	err |= __put_user(current->used_math, &sc->sc_used_math);
+	err |= __put_user(!!used_math(), &sc->sc_used_math);
 
-	if (!current->used_math)
+	if (!used_math())
 		goto out;
 
 	/*
--- x/arch/mips/kernel/signal32.c.~1~	2004-12-04 08:56:20.000000000 +0100
+++ x/arch/mips/kernel/signal32.c	2004-12-25 15:18:54.606976960 +0100
@@ -361,11 +361,11 @@ static asmlinkage int restore_sigcontext
 	restore_gp_reg(31);
 #undef restore_gp_reg
 
-	err |= __get_user(current->used_math, &sc->sc_used_math);
+	err |= __get_user(!!used_math(), &sc->sc_used_math);
 
 	preempt_disable();
 
-	if (current->used_math) {
+	if (used_math()) {
 		/* restore fpu context if we have used it before */
 		own_fpu();
 		err |= restore_fp_context32(sc);
@@ -552,9 +552,9 @@ static inline int setup_sigcontext32(str
 	err |= __put_user(regs->cp0_cause, &sc->sc_cause);
 	err |= __put_user(regs->cp0_badvaddr, &sc->sc_badvaddr);
 
-	err |= __put_user(current->used_math, &sc->sc_used_math);
+	err |= __put_user(!!used_math(), &sc->sc_used_math);
 
-	if (!current->used_math)
+	if (!used_math())
 		goto out;
 
 	/* 
--- x/arch/mips/kernel/traps.c.~1~	2004-12-04 08:56:20.000000000 +0100
+++ x/arch/mips/kernel/traps.c	2004-12-25 15:18:54.608976656 +0100
@@ -655,11 +655,11 @@ asmlinkage void do_cpu(struct pt_regs *r
 		preempt_disable();
 
 		own_fpu();
-		if (current->used_math) {	/* Using the FPU again.  */
+		if (used_math()) {	/* Using the FPU again.  */
 			restore_fp(current);
 		} else {			/* First time FPU user.  */
 			init_fpu();
-			current->used_math = 1;
+			set_used_math();
 		}
 
 		if (!cpu_has_fpu) {
--- x/arch/s390/kernel/process.c.~1~	2004-12-04 08:56:20.000000000 +0100
+++ x/arch/s390/kernel/process.c	2004-12-25 15:18:54.609976504 +0100
@@ -216,8 +216,7 @@ void exit_thread(void)
 
 void flush_thread(void)
 {
-
-        current->used_math = 0;
+	clear_used_math();
 	clear_tsk_thread_flag(current, TIF_USEDFPU);
 }
 
--- x/arch/s390/kernel/setup.c.~1~	2004-12-04 08:54:54.000000000 +0100
+++ x/arch/s390/kernel/setup.c	2004-12-25 15:18:54.610976352 +0100
@@ -96,7 +96,7 @@ void __devinit cpu_init (void)
          * Force FPU initialization:
          */
         clear_thread_flag(TIF_USEDFPU);
-        current->used_math = 0;
+        clear_used_math();
 
         /* Setup active_mm for idle_task  */
         atomic_inc(&init_mm.mm_count);
--- x/arch/sh/kernel/cpu/sh4/fpu.c.~1~	2004-02-20 17:26:36.000000000 +0100
+++ x/arch/sh/kernel/cpu/sh4/fpu.c	2004-12-25 15:18:54.611976200 +0100
@@ -323,13 +323,13 @@ do_fpu_state_restore(unsigned long r4, u
 		return;
 	}
 
-	if (tsk->used_math) {
+	if (used_math()) {
 		/* Using the FPU again.  */
 		restore_fpu(tsk);
 	} else	{
 		/* First time FPU user.  */
 		fpu_init();
-		tsk->used_math = 1;
+		set_used_math();
 	}
 	set_tsk_thread_flag(tsk, TIF_USEDFPU);
 }
--- x/arch/sh/kernel/cpu/init.c.~1~	2004-12-04 08:56:20.000000000 +0100
+++ x/arch/sh/kernel/cpu/init.c	2004-12-25 15:18:54.611976200 +0100
@@ -194,7 +194,7 @@ asmlinkage void __init sh_cpu_init(void)
 	/* FPU initialization */
 	if ((cpu_data->flags & CPU_HAS_FPU)) {
 		clear_thread_flag(TIF_USEDFPU);
-		current->used_math = 0;
+		clear_used_math();
 	}
 
 #ifdef CONFIG_SH_DSP
--- x/arch/sh/kernel/process.c.~1~	2004-12-04 08:56:21.000000000 +0100
+++ x/arch/sh/kernel/process.c	2004-12-25 15:18:54.612976048 +0100
@@ -208,7 +208,7 @@ void flush_thread(void)
 
 	/* Forget lazy FPU state */
 	clear_fpu(tsk, regs);
-	tsk->used_math = 0;
+	clear_used_math();
 #endif
 }
 
@@ -225,7 +225,7 @@ int dump_fpu(struct pt_regs *regs, elf_f
 #if defined(CONFIG_SH_FPU)
 	struct task_struct *tsk = current;
 
-	fpvalid = tsk->used_math;
+	fpvalid = !!tsk_used_math(tsk);
 	if (fpvalid) {
 		unlazy_fpu(tsk, regs);
 		memcpy(fpu, &tsk->thread.fpu.hard, sizeof(*fpu));
@@ -260,7 +260,7 @@ dump_task_fpu (struct task_struct *tsk, 
 	int fpvalid = 0;
 
 #if defined(CONFIG_SH_FPU)
-	fpvalid = tsk->used_math;
+	fpvalid = !!tsk_used_math(tsk);
 	if (fpvalid) {
 		struct pt_regs *regs = (struct pt_regs *)
 					((unsigned long)tsk->thread_info
@@ -286,7 +286,7 @@ int copy_thread(int nr, unsigned long cl
 
 	unlazy_fpu(tsk, regs);
 	p->thread.fpu = tsk->thread.fpu;
-	p->used_math = tsk->used_math;
+	copy_to_stopped_child_used_math(p);
 #endif
 
 	childregs = ((struct pt_regs *)
--- x/arch/sh/kernel/ptrace.c.~1~	2004-12-04 08:56:21.000000000 +0100
+++ x/arch/sh/kernel/ptrace.c	2004-12-25 15:18:54.613975896 +0100
@@ -150,7 +150,7 @@ asmlinkage int sys_ptrace(long request, 
 			tmp = get_stack_long(child, addr);
 		else if (addr >= (long) &dummy->fpu &&
 			 addr < (long) &dummy->u_fpvalid) {
-			if (!child->used_math) {
+			if (!tsk_used_math(child)) {
 				if (addr == (long)&dummy->fpu.fpscr)
 					tmp = FPSCR_INIT;
 				else
@@ -159,7 +159,7 @@ asmlinkage int sys_ptrace(long request, 
 				tmp = ((long *)&child->thread.fpu)
 					[(addr - (long)&dummy->fpu) >> 2];
 		} else if (addr == (long) &dummy->u_fpvalid)
-			tmp = child->used_math;
+			tmp = !!tsk_used_math(child);
 		else
 			tmp = 0;
 		ret = put_user(tmp, (unsigned long *)data);
@@ -185,12 +185,12 @@ asmlinkage int sys_ptrace(long request, 
 			ret = put_stack_long(child, addr, data);
 		else if (addr >= (long) &dummy->fpu &&
 			 addr < (long) &dummy->u_fpvalid) {
-			child->used_math = 1;
+			set_stopped_child_used_math(child);
 			((long *)&child->thread.fpu)
 				[(addr - (long)&dummy->fpu) >> 2] = data;
 			ret = 0;
 		} else if (addr == (long) &dummy->u_fpvalid) {
-			child->used_math = data?1:0;
+			conditional_stopped_child_used_math(data, child);
 			ret = 0;
 		}
 		break;
--- x/arch/sh/kernel/signal.c.~1~	2004-12-04 08:56:21.000000000 +0100
+++ x/arch/sh/kernel/signal.c	2004-12-25 15:18:54.614975744 +0100
@@ -163,7 +163,7 @@ static inline int restore_sigcontext_fpu
 	if (!(cpu_data->flags & CPU_HAS_FPU))
 		return 0;
 
-	tsk->used_math = 1;
+	set_used_math();
 	return __copy_from_user(&tsk->thread.fpu.hard, &sc->sc_fpregs[0],
 				sizeof(long)*(16*2+2));
 }
@@ -176,7 +176,7 @@ static inline int save_sigcontext_fpu(st
 	if (!(cpu_data->flags & CPU_HAS_FPU))
 		return 0;
 
-	if (!tsk->used_math) {
+	if (!used_math()) {
 		__put_user(0, &sc->sc_ownedfp);
 		return 0;
 	}
@@ -186,7 +186,7 @@ static inline int save_sigcontext_fpu(st
 	/* This will cause a "finit" to be triggered by the next
 	   attempted FPU operation by the 'current' process.
 	   */
-	tsk->used_math = 0;
+	clear_used_math();
 
 	unlazy_fpu(tsk, regs);
 	return __copy_to_user(&sc->sc_fpregs[0], &tsk->thread.fpu.hard,
@@ -220,7 +220,7 @@ restore_sigcontext(struct pt_regs *regs,
 
 		regs->sr |= SR_FD; /* Release FPU */
 		clear_fpu(tsk, regs);
-		tsk->used_math = 0;
+		clear_used_math();
 		__get_user (owned_fp, &sc->sc_ownedfp);
 		if (owned_fp)
 			err |= restore_sigcontext_fpu(sc);
--- x/arch/sh64/kernel/fpu.c.~1~	2004-08-25 02:47:49.000000000 +0200
+++ x/arch/sh64/kernel/fpu.c	2004-12-25 15:18:54.615975592 +0100
@@ -158,12 +158,12 @@ do_fpu_state_restore(unsigned long ex, s
 		fpsave(&last_task_used_math->thread.fpu.hard);
         }
         last_task_used_math = current;
-        if (current->used_math) {
+        if (used_math()) {
                 fpload(&current->thread.fpu.hard);
         } else {
 		/* First time FPU user.  */
 		fpload(&init_fpuregs.hard);
-                current->used_math = 1;
+                set_used_math();
         }
 	release_fpu();
 }
--- x/arch/sh64/kernel/process.c.~1~	2004-12-04 08:56:21.000000000 +0100
+++ x/arch/sh64/kernel/process.c	2004-12-25 15:18:54.616975440 +0100
@@ -688,7 +688,7 @@ void flush_thread(void)
 		last_task_used_math = NULL;
 	}
 	/* Force FPU state to be reinitialised after exec */
-	current->used_math = 0;
+	clear_used_math();
 #endif
 
 	/* if we are a kernel thread, about to change to user thread,
@@ -713,7 +713,7 @@ int dump_fpu(struct pt_regs *regs, elf_f
 	int fpvalid;
 	struct task_struct *tsk = current;
 
-	fpvalid = tsk->used_math;
+	fpvalid = !!tsk_used_math(tsk);
 	if (fpvalid) {
 		if (current == last_task_used_math) {
 			grab_fpu();
--- x/arch/sh64/kernel/ptrace.c.~1~	2004-12-04 08:56:21.000000000 +0100
+++ x/arch/sh64/kernel/ptrace.c	2004-12-25 15:18:54.617975288 +0100
@@ -63,7 +63,7 @@ get_fpu_long(struct task_struct *task, u
 	struct pt_regs *regs;
 	regs = (struct pt_regs*)((unsigned char *)task + THREAD_SIZE) - 1;
 
-	if (!task->used_math) {
+	if (!tsk_used_math(task)) {
 		if (addr == offsetof(struct user_fpu_struct, fpscr)) {
 			tmp = FPSCR_INIT;
 		} else {
@@ -105,9 +105,9 @@ put_fpu_long(struct task_struct *task, u
 
 	regs = (struct pt_regs*)((unsigned char *)task + THREAD_SIZE) - 1;
 
-	if (!task->used_math) {
+	if (!tsk_used_math(task)) {
 		fpinit(&task->thread.fpu.hard);
-		task->used_math = 1;
+		set_stopped_child_used_math(task);
 	} else if (last_task_used_math == task) {
 		grab_fpu();
 		fpsave(&task->thread.fpu.hard);
@@ -187,7 +187,7 @@ asmlinkage int sys_ptrace(long request, 
 			 (addr <  offsetof(struct user, u_fpvalid))) {
 			tmp = get_fpu_long(child, addr - offsetof(struct user, fpu));
 		} else if (addr == offsetof(struct user, u_fpvalid)) {
-			tmp = child->used_math;
+			tmp = !!tsk_used_math(child);
 		} else {
 			break;
 		}
--- x/arch/sh64/kernel/signal.c.~1~	2004-12-04 08:54:54.000000000 +0100
+++ x/arch/sh64/kernel/signal.c	2004-12-25 15:18:54.618975136 +0100
@@ -186,7 +186,7 @@ restore_sigcontext_fpu(struct pt_regs *r
 	int fpvalid;
 
 	err |= __get_user (fpvalid, &sc->sc_fpvalid);
-	current->used_math = fpvalid;
+	conditional_used_math(fpvalid);
 	if (! fpvalid)
 		return err;
 
@@ -207,7 +207,7 @@ setup_sigcontext_fpu(struct pt_regs *reg
 	int err = 0;
 	int fpvalid;
 
-	fpvalid = current->used_math;
+	fpvalid = !!used_math();
 	err |= __put_user(fpvalid, &sc->sc_fpvalid);
 	if (! fpvalid)
 		return err;
@@ -222,7 +222,7 @@ setup_sigcontext_fpu(struct pt_regs *reg
 
 	err |= __copy_to_user(&sc->sc_fpregs[0], &current->thread.fpu.hard,
 			      (sizeof(long long) * 32) + (sizeof(int) * 1));
-	current->used_math = 0;
+	clear_used_math();
 
 	return err;
 }
--- x/arch/sparc/kernel/process.c.~1~	2004-12-04 08:56:21.000000000 +0100
+++ x/arch/sparc/kernel/process.c	2004-12-25 15:18:54.619974984 +0100
@@ -602,7 +602,7 @@ void dump_thread(struct pt_regs * regs, 
  */
 int dump_fpu (struct pt_regs * regs, elf_fpregset_t * fpregs)
 {
-	if (current->used_math == 0) {
+	if (used_math()) {
 		memset(fpregs, 0, sizeof(*fpregs));
 		fpregs->pr_q_entrysize = 8;
 		return 1;
--- x/arch/sparc/kernel/signal.c.~1~	2004-12-04 08:56:21.000000000 +0100
+++ x/arch/sparc/kernel/signal.c	2004-12-25 15:18:54.621974680 +0100
@@ -202,7 +202,7 @@ restore_fpu_state(struct pt_regs *regs, 
 		regs->psr &= ~PSR_EF;
 	}
 #endif
-	current->used_math = 1;
+	set_used_math();
 	clear_tsk_thread_flag(current, TIF_USEDFPU);
 
 	if (verify_area(VERIFY_READ, fpu, sizeof(*fpu)))
@@ -584,7 +584,7 @@ save_fpu_state(struct pt_regs *regs, __s
 				      &current->thread.fpqueue[0],
 				      ((sizeof(unsigned long) +
 				      (sizeof(unsigned long *)))*16));
-	current->used_math = 0;
+	clear_used_math();
 	return err;
 }
 
@@ -599,7 +599,7 @@ new_setup_frame(struct k_sigaction *ka, 
 	synchronize_user_stack();
 
 	sigframe_size = NF_ALIGNEDSZ;
-	if (!current->used_math)
+	if (!used_math())
 		sigframe_size -= sizeof(__siginfo_fpu_t);
 
 	sf = (struct new_signal_frame __user *)
@@ -616,7 +616,7 @@ new_setup_frame(struct k_sigaction *ka, 
 	
 	err |= __put_user(0, &sf->extra_size);
 
-	if (current->used_math) {
+	if (used_math()) {
 		err |= save_fpu_state(regs, &sf->fpu_state);
 		err |= __put_user(&sf->fpu_state, &sf->fpu_save);
 	} else {
@@ -677,7 +677,7 @@ new_setup_rt_frame(struct k_sigaction *k
 
 	synchronize_user_stack();
 	sigframe_size = RT_ALIGNEDSZ;
-	if (!current->used_math)
+	if (!used_math())
 		sigframe_size -= sizeof(__siginfo_fpu_t);
 	sf = (struct rt_signal_frame __user *)
 		get_sigframe(&ka->sa, regs, sigframe_size);
@@ -690,7 +690,7 @@ new_setup_rt_frame(struct k_sigaction *k
 	err |= __put_user(regs->npc, &sf->regs.npc);
 	err |= __put_user(regs->y, &sf->regs.y);
 	psr = regs->psr;
-	if (current->used_math)
+	if (used_math())
 		psr |= PSR_EF;
 	err |= __put_user(psr, &sf->regs.psr);
 	err |= __copy_to_user(&sf->regs.u_regs, regs->u_regs, sizeof(regs->u_regs));
--- x/arch/sparc/kernel/traps.c.~1~	2004-08-25 02:47:49.000000000 +0200
+++ x/arch/sparc/kernel/traps.c	2004-12-25 15:18:54.622974528 +0100
@@ -246,17 +246,17 @@ void do_fpd_trap(struct pt_regs *regs, u
 		       &fptask->thread.fpqueue[0], &fptask->thread.fpqdepth);
 	}
 	last_task_used_math = current;
-	if(current->used_math) {
+	if(used_math()) {
 		fpload(&current->thread.float_regs[0], &current->thread.fsr);
 	} else {
 		/* Set initial sane state. */
 		fpload(&init_fregs[0], &init_fsr);
-		current->used_math = 1;
+		set_used_math();
 	}
 #else
-	if(!current->used_math) {
+	if(!used_math()) {
 		fpload(&init_fregs[0], &init_fsr);
-		current->used_math = 1;
+		set_used_math();
 	} else {
 		fpload(&current->thread.float_regs[0], &current->thread.fsr);
 	}
--- x/arch/x86_64/ia32/fpu32.c.~1~	2004-08-25 02:47:33.000000000 +0200
+++ x/arch/x86_64/ia32/fpu32.c	2004-12-25 15:18:54.623974376 +0100
@@ -156,7 +156,7 @@ int restore_i387_ia32(struct task_struct
 				     sizeof(struct i387_fxsave_struct)))
 			return -1;
 		tsk->thread.i387.fxsave.mxcsr &= mxcsr_feature_mask;
-		tsk->used_math = 1;
+		set_stopped_child_used_math(tsk);
 	} 
 	return convert_fxsr_from_user(&tsk->thread.i387.fxsave, buf);
 }  
--- x/arch/x86_64/ia32/ia32_binfmt.c.~1~	2004-12-04 08:56:21.000000000 +0100
+++ x/arch/x86_64/ia32/ia32_binfmt.c	2004-12-25 15:18:54.624974224 +0100
@@ -214,7 +214,7 @@ elf_core_copy_task_fpregs(struct task_st
 	struct _fpstate_ia32 *fpstate = (void*)fpu; 
 	mm_segment_t oldfs = get_fs();
 
-	if (!tsk->used_math) 
+	if (!tsk_used_math(tsk)) 
 		return 0;
 	if (!regs)
 		regs = (struct pt_regs *)tsk->thread.rsp0;
@@ -235,7 +235,7 @@ static inline int 
 elf_core_copy_task_xfpregs(struct task_struct *t, elf_fpxregset_t *xfpu)
 {
 	struct pt_regs *regs = ((struct pt_regs *)(t->thread.rsp0))-1; 
-	if (!t->used_math) 
+	if (!tsk_used_math(t)) 
 		return 0;
 	if (t == current)
 		unlazy_fpu(t); 
--- x/arch/x86_64/ia32/ia32_signal.c.~1~	2004-12-04 08:54:54.000000000 +0100
+++ x/arch/x86_64/ia32/ia32_signal.c	2004-12-25 15:18:54.625974072 +0100
@@ -383,7 +383,7 @@ ia32_setup_sigcontext(struct sigcontext_
 	if (tmp < 0)
 	  err = -EFAULT;
 	else { 
-		current->used_math = 0;
+		clear_used_math();
 		stts();
 	  err |= __put_user((u32)(u64)(tmp ? fpstate : NULL), &sc->fpstate);
 	}
--- x/arch/x86_64/ia32/ptrace32.c.~1~	2004-12-04 08:56:21.000000000 +0100
+++ x/arch/x86_64/ia32/ptrace32.c	2004-12-25 15:18:54.625974072 +0100
@@ -358,7 +358,7 @@ asmlinkage long sys32_ptrace(long reques
 			break;
 		/* no checking to be bug-to-bug compatible with i386 */
 		__copy_from_user(&child->thread.i387.fxsave, u, sizeof(*u));
-		child->used_math = 1;
+		set_stopped_child_used_math(child);
 		child->thread.i387.fxsave.mxcsr &= mxcsr_feature_mask;
 		ret = 0; 
 		break;
--- x/arch/x86_64/kernel/i387.c.~1~	2004-08-25 02:47:33.000000000 +0200
+++ x/arch/x86_64/kernel/i387.c	2004-12-25 15:18:54.626973920 +0100
@@ -57,12 +57,12 @@ void __init fpu_init(void)
 	mxcsr_feature_mask_init();
 	/* clean state in init */
 	current_thread_info()->status = 0;
-	current->used_math = 0;
+	clear_used_math();
 }
 
 void init_fpu(struct task_struct *child)
 {
-	if (child->used_math) { 
+	if (tsk_used_math(child)) { 
 		if (child == current)
 			unlazy_fpu(child);
 		return;
@@ -70,7 +70,8 @@ void init_fpu(struct task_struct *child)
 	memset(&child->thread.i387.fxsave, 0, sizeof(struct i387_fxsave_struct));
 	child->thread.i387.fxsave.cwd = 0x37f;
 	child->thread.i387.fxsave.mxcsr = 0x1f80;
-	child->used_math = 1;
+	/* only the device not available exception or ptrace can call init_fpu */
+	set_stopped_child_used_math(child);
 }
 
 /*
@@ -91,9 +92,9 @@ int save_i387(struct _fpstate __user *bu
 	if ((unsigned long)buf % 16) 
 		printk("save_i387: bad fpstate %p\n",buf); 
 
-	if (!tsk->used_math) 
+	if (!used_math()) 
 		return 0;
-	tsk->used_math = 0; /* trigger finit */ 
+	clear_used_math(); /* trigger finit */ 
 	if (tsk->thread_info->status & TS_USEDFPU) {
 		err = save_i387_checking((struct i387_fxsave_struct __user *)buf);
 		if (err) return err;
@@ -133,7 +134,7 @@ int dump_fpu( struct pt_regs *regs, stru
 {
 	struct task_struct *tsk = current;
 
-	if (!tsk->used_math) 
+	if (!used_math()) 
 		return 0;
 
 	unlazy_fpu(tsk);
@@ -143,7 +144,7 @@ int dump_fpu( struct pt_regs *regs, stru
 
 int dump_task_fpu(struct task_struct *tsk, struct user_i387_struct *fpu)
 {
-	int fpvalid = tsk->used_math;
+	int fpvalid = !!tsk_used_math(tsk);
 
 	if (fpvalid) {
 		if (tsk == current)
--- x/arch/x86_64/kernel/process.c.~1~	2004-12-04 08:56:21.000000000 +0100
+++ x/arch/x86_64/kernel/process.c	2004-12-25 15:18:54.627973768 +0100
@@ -297,7 +297,7 @@ void flush_thread(void)
 	 * Forget coprocessor state..
 	 */
 	clear_fpu(tsk);
-	tsk->used_math = 0;
+	clear_used_math();
 }
 
 void release_thread(struct task_struct *dead_task)
--- x/arch/x86_64/kernel/ptrace.c.~1~	2004-12-04 08:56:21.000000000 +0100
+++ x/arch/x86_64/kernel/ptrace.c	2004-12-25 15:18:54.628973616 +0100
@@ -480,7 +480,7 @@ asmlinkage long sys_ptrace(long request,
 			ret = -EIO;
 			break;
 		}
-		child->used_math = 1;
+		set_stopped_child_used_math(child);
 		ret = set_fpregs(child, (struct user_i387_struct __user *)data);
 		break;
 	}
--- x/arch/x86_64/kernel/signal.c.~1~	2004-12-04 08:56:21.000000000 +0100
+++ x/arch/x86_64/kernel/signal.c	2004-12-25 15:18:54.629973464 +0100
@@ -246,7 +246,7 @@ static void setup_rt_frame(int sig, stru
 	int err = 0;
 	struct task_struct *me = current;
 
-	if (me->used_math) {
+	if (used_math()) {
 		fp = get_stack(ka, regs, sizeof(struct _fpstate)); 
 		frame = (void __user *)round_down((unsigned long)fp - sizeof(struct rt_sigframe), 16) - 8;
 
--- x/arch/x86_64/kernel/traps.c.~1~	2004-12-04 08:56:21.000000000 +0100
+++ x/arch/x86_64/kernel/traps.c	2004-12-25 15:18:54.630973312 +0100
@@ -894,7 +894,7 @@ asmlinkage void math_state_restore(void)
 	struct task_struct *me = current;
 	clts();			/* Allow maths ops (or we recurse) */
 
-	if (!me->used_math)
+	if (!used_math())
 		init_fpu(me);
 	restore_fpu_checking(&me->thread.i387.fxsave);
 	me->thread_info->status |= TS_USEDFPU;
--- x/arch/m32r/kernel/ptrace.c.~1~	2004-12-04 08:56:19.000000000 +0100
+++ x/arch/m32r/kernel/ptrace.c	2004-12-25 15:22:37.271126864 +0100
@@ -130,7 +130,7 @@ static int ptrace_read_user(struct task_
 #ifndef NO_FPU
 		else if (off >= (long)(&dummy->fpu >> 2) &&
 			 off < (long)(&dummy->u_fpvalid >> 2)) {
-			if (!tsk->used_math) {
+			if (!tsk_used_math(tsk)) {
 				if (off == (long)(&dummy->fpu.fpscr >> 2))
 					tmp = FPSCR_INIT;
 				else
@@ -139,7 +139,7 @@ static int ptrace_read_user(struct task_
 				tmp = ((long *)(&tsk->thread.fpu >> 2))
 					[off - (long)&dummy->fpu];
 		} else if (off == (long)(&dummy->u_fpvalid >> 2))
-			tmp = tsk->used_math;
+			tmp = !!tsk_used_math(tsk);
 #endif /* not NO_FPU */
 		else
 			tmp = 0;
@@ -187,12 +187,12 @@ static int ptrace_write_user(struct task
 #ifndef NO_FPU
 		else if (off >= (long)(&dummy->fpu >> 2) &&
 			 off < (long)(&dummy->u_fpvalid >> 2)) {
-			tsk->used_math = 1;
+			set_stopped_child_used_math(tsk);
 			((long *)&tsk->thread.fpu)
 				[off - (long)&dummy->fpu] = data;
 			ret = 0;
 		} else if (off == (long)(&dummy->u_fpvalid >> 2)) {
-			tsk->used_math = data ? 1 : 0;
+			conditional_stopped_child_used_math(data, tsk);
 			ret = 0;
 		}
 #endif /* not NO_FPU */
--- x/arch/m32r/kernel/setup.c.~1~	2004-12-04 08:54:53.000000000 +0100
+++ x/arch/m32r/kernel/setup.c	2004-12-25 15:18:54.632973008 +0100
@@ -389,7 +389,7 @@ void __init cpu_init (void)
 
 	/* Force FPU initialization */
 	current_thread_info()->status = 0;
-	current->used_math = 0;
+	clear_used_math();
 
 #ifdef CONFIG_MMU
 	/* Set up MMU */
--- x/include/asm-arm26/constants.h.~1~	2003-06-08 18:21:42.000000000 +0200
+++ x/include/asm-arm26/constants.h	2004-12-25 15:18:54.633972856 +0100
@@ -7,7 +7,6 @@
  *
  */
 
-#define TSK_USED_MATH 788 /* offsetof(struct task_struct, used_math) */
 #define TSK_ACTIVE_MM 96 /* offsetof(struct task_struct, active_mm) */
 
 #define VMA_VM_MM 0 /* offsetof(struct vm_area_struct, vm_mm) */
--- x/include/asm-x86_64/i387.h.~1~	2004-12-04 08:55:04.000000000 +0100
+++ x/include/asm-x86_64/i387.h	2004-12-25 15:18:54.633972856 +0100
@@ -25,16 +25,6 @@ extern void mxcsr_feature_mask_init(void
 extern void init_fpu(struct task_struct *child);
 extern int save_i387(struct _fpstate __user *buf);
 
-static inline int need_signal_i387(struct task_struct *me) 
-{ 
-	if (!me->used_math)
-		return 0;
-	me->used_math = 0; 
-	if (me->thread_info->status & TS_USEDFPU)
-		return 0;
-	return 1;
-} 
-
 /*
  * FPU lazy state save handling...
  */
--- x/include/linux/sched.h.~1~	2004-12-25 03:59:16.000000000 +0100
+++ x/include/linux/sched.h	2004-12-25 15:18:54.635972552 +0100
@@ -600,19 +600,7 @@ struct task_struct {
 	struct key *process_keyring;	/* keyring private to this process (CLONE_THREAD) */
 	struct key *thread_keyring;	/* keyring private to this thread */
 #endif
-/*
- * Must be changed atomically so it shouldn't be
- * be a shareable bitflag.
- */
-	unsigned char used_math;
-/*
- * OOM kill score adjustment (bit shift).
- * Cannot live together with used_math since
- * used_math and oomkilladj can be changed at the
- * same time, so they would race if they're in the
- * same atomic block.
- */
-	short oomkilladj;
+	int oomkilladj; /* OOM kill score adjustment (bit shift). */
 	char comm[16];
 /* file system info */
 	int link_count, total_link_count;
@@ -674,7 +662,7 @@ struct task_struct {
 	wait_queue_t *io_wait;
 #ifdef CONFIG_NUMA
   	struct mempolicy *mempolicy;
-  	short il_next;		/* could be shared with used_math */
+  	short il_next;
 #endif
 };
 
@@ -716,7 +704,7 @@ do { if (atomic_dec_and_test(&(tsk)->usa
 #define PF_SIGNALED	0x00000400	/* killed by a signal */
 #define PF_MEMALLOC	0x00000800	/* Allocating memory */
 #define PF_FLUSHER	0x00001000	/* responsible for disk writeback */
-
+#define PF_USED_MATH	0x00002000	/* if unset the fpu must be initialized before use */
 #define PF_FREEZE	0x00004000	/* this task should be frozen for suspend */
 #define PF_NOFREEZE	0x00008000	/* this thread should not be frozen */
 #define PF_FROZEN	0x00010000	/* frozen for system suspend */
@@ -727,6 +715,31 @@ do { if (atomic_dec_and_test(&(tsk)->usa
 #define PF_SYNCWRITE	0x00200000	/* I am doing a sync write */
 #define PF_BORROWED_MM	0x00400000	/* I am a kthread doing use_mm */
 
+/*
+ * Only the _current_ task can read/write to tsk->flags, but other
+ * tasks can access tsk->flags in readonly mode for example
+ * with tsk_used_math (like during threaded core dumping).
+ * There is however an exception to this rule during ptrace
+ * or during fork: the ptracer task is allowed to write to the
+ * child->flags of its traced child (same goes for fork, the parent
+ * can write to the child->flags), because we're guaranteed the
+ * child is not running and in turn not changing child->flags
+ * at the same time the parent does it.
+ */
+#define clear_stopped_child_used_math(child) do { (child)->flags &= ~PF_USED_MATH; } while (0)
+#define set_stopped_child_used_math(child) do { (child)->flags |= PF_USED_MATH; } while (0)
+#define clear_used_math() clear_stopped_child_used_math(current)
+#define set_used_math() set_stopped_child_used_math(current)
+#define conditional_stopped_child_used_math(condition, child) \
+	do { (child)->flags &= ~PF_USED_MATH, (child)->flags |= (condition) ? PF_USED_MATH : 0; } while (0)
+#define conditional_used_math(condition) \
+	conditional_stopped_child_used_math(condition, current)
+#define copy_to_stopped_child_used_math(child) \
+	do { (child)->flags &= ~PF_USED_MATH, (child)->flags |= current->flags & PF_USED_MATH; } while (0)
+/* NOTE: this will return 0 or PF_USED_MATH, it will never return 1 */
+#define tsk_used_math(p) ((p)->flags & PF_USED_MATH)
+#define used_math() tsk_used_math(current)
+
 #ifdef CONFIG_SMP
 extern int set_cpus_allowed(task_t *p, cpumask_t new_mask);
 #else