[PATCH 1/3] do_fpe() cleanup

[PATCH 1/3] do_fpe() cleanup

[Atsushi Nemoto]

If we had already lost FPU before disabling preempt, we do not have to
own it at all.  And we do not prevent preemption when managing saved
FCR31 if we did not have FPU ownership.

Signed-off-by: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
---
 traps.c |   22 ++++++++--------------
 1 files changed, 8 insertions(+), 14 deletions(-)

diff --git a/arch/mips/kernel/traps.c b/arch/mips/kernel/traps.c
index 9fda1b8..b18aeb6 100644
--- a/arch/mips/kernel/traps.c
+++ b/arch/mips/kernel/traps.c
@@ -614,16 +614,6 @@ asmlinkage void do_fpe(struct pt_regs *r
 	if (fcr31 & FPU_CSR_UNI_X) {
 		int sig;
 
-		preempt_disable();
-
-#ifdef CONFIG_PREEMPT
-		if (!is_fpu_owner()) {
-			/* We might lose fpu before disabling preempt... */
-			own_fpu();
-			BUG_ON(!used_math());
-			restore_fp(current);
-		}
-#endif
 		/*
 		 * Unimplemented operation exception.  If we've got the full
 		 * software emulator on-board, let's use it...
@@ -634,7 +624,11 @@ #endif
 		 * register operands before invoking the emulator, which seems
 		 * a bit extreme for what should be an infrequent event.
 		 */
-		save_fp(current);
+		preempt_disable();
+
+		/* We might have lost fpu before disabling preempt... */
+		if (is_fpu_owner())
+			save_fp(current);
 		/* Ensure 'resume' not overwrite saved fp context again. */
 		lose_fpu();
 
@@ -643,15 +637,15 @@ #endif
 		/* Run the emulator */
 		sig = fpu_emulator_cop1Handler (regs, &current->thread.fpu, 1);
 
-		preempt_disable();
-
-		own_fpu();	/* Using the FPU again.  */
 		/*
 		 * We can't allow the emulated instruction to leave any of
 		 * the cause bit set in $fcr31.
 		 */
 		current->thread.fpu.fcr31 &= ~FPU_CSR_ALL_X;
 
+		preempt_disable();
+
+		own_fpu();	/* Using the FPU again.  */
 		/* Restore the hardware register state */
 		restore_fp(current);
 

Re: [PATCH 1/3] do_fpe() cleanup

[Atsushi Nemoto]

On Sat, 25 Nov 2006 00:03:44 +0900 (JST), Atsushi Nemoto <anemo@mba.ocn.ne.jp> wrote:
> If we had already lost FPU before disabling preempt, we do not have to
> own it at all.  And we do not prevent preemption when managing saved
> FCR31 if we did not have FPU ownership.
> 
> Signed-off-by: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
> ---
>  traps.c |   22 ++++++++--------------
>  1 files changed, 8 insertions(+), 14 deletions(-)

Ping.  This patch is dependent from other fp_context patches and
should be safe and harmless.  Are there any problems?


diff --git a/arch/mips/kernel/traps.c b/arch/mips/kernel/traps.c
index 9fda1b8..b18aeb6 100644
--- a/arch/mips/kernel/traps.c
+++ b/arch/mips/kernel/traps.c
@@ -614,16 +614,6 @@ asmlinkage void do_fpe(struct pt_regs *r
 	if (fcr31 & FPU_CSR_UNI_X) {
 		int sig;
 
-		preempt_disable();
-
-#ifdef CONFIG_PREEMPT
-		if (!is_fpu_owner()) {
-			/* We might lose fpu before disabling preempt... */
-			own_fpu();
-			BUG_ON(!used_math());
-			restore_fp(current);
-		}
-#endif
 		/*
 		 * Unimplemented operation exception.  If we've got the full
 		 * software emulator on-board, let's use it...
@@ -634,7 +624,11 @@ #endif
 		 * register operands before invoking the emulator, which seems
 		 * a bit extreme for what should be an infrequent event.
 		 */
-		save_fp(current);
+		preempt_disable();
+
+		/* We might have lost fpu before disabling preempt... */
+		if (is_fpu_owner())
+			save_fp(current);
 		/* Ensure 'resume' not overwrite saved fp context again. */
 		lose_fpu();
 
@@ -643,15 +637,15 @@ #endif
 		/* Run the emulator */
 		sig = fpu_emulator_cop1Handler (regs, &current->thread.fpu, 1);
 
-		preempt_disable();
-
-		own_fpu();	/* Using the FPU again.  */
 		/*
 		 * We can't allow the emulated instruction to leave any of
 		 * the cause bit set in $fcr31.
 		 */
 		current->thread.fpu.fcr31 &= ~FPU_CSR_ALL_X;
 
+		preempt_disable();
+
+		own_fpu();	/* Using the FPU again.  */
 		/* Restore the hardware register state */
 		restore_fp(current);