PREEMPT_RT + HIGHMEM = segfaults during boot on ppc32

PREEMPT_RT + HIGHMEM = segfaults during boot on ppc32

[Steve Rottinger]

Hi,

I'm using 2.6.29.5-rt22 on a custom ppc32 (8641D) board.  About half the
time, the board will boot up correctly. The other half of the time, I'll
get segfaults in various parts of the init process.  I've also noticed
that if I remove CONFIG_HIGHMEM from my configuration, I am able to boot
consistently without running into this problem.  Is there anyone else
experiencing this, or does anyone have any suggestions?

Thanks in advance,

-Steve

Re: PREEMPT_RT + HIGHMEM = segfaults during boot on ppc32

[Thomas Gleixner]

Steve,

On Thu, 2 Jul 2009, Steve Rottinger wrote:
> I'm using 2.6.29.5-rt22 on a custom ppc32 (8641D) board.  About half the
> time, the board will boot up correctly. The other half of the time, I'll
> get segfaults in various parts of the init process.  I've also noticed
> that if I remove CONFIG_HIGHMEM from my configuration, I am able to boot
> consistently without running into this problem.  Is there anyone else
> experiencing this, or does anyone have any suggestions?

does the patch below help ?

Thanks,

	tglx
---
Subject: powerpc-fixup-pagefault-disable-changes.patch
From: Thomas Gleixner <tglx@linutronix.de>
Date: Mon, 06 Jul 2009 17:36:01 +0200

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
 arch/powerpc/include/asm/highmem.h |    3 +++
 1 file changed, 3 insertions(+)

Index: linux-2.6-tip/arch/powerpc/include/asm/highmem.h
===================================================================
--- linux-2.6-tip.orig/arch/powerpc/include/asm/highmem.h
+++ linux-2.6-tip/arch/powerpc/include/asm/highmem.h
@@ -90,6 +90,7 @@ static inline void *kmap_atomic_prot(str
 	unsigned long vaddr;
 
 	/* even !CONFIG_PREEMPT needs this, for in_atomic in do_page_fault */
+	preempt_disable();
 	pagefault_disable();
 	if (!PageHighMem(page))
 		return page_address(page);
@@ -118,6 +119,7 @@ static inline void kunmap_atomic(void *k
 
 	if (vaddr < __fix_to_virt(FIX_KMAP_END)) {
 		pagefault_enable();
+		preempt_enable();
 		return;
 	}
 
@@ -131,6 +133,7 @@ static inline void kunmap_atomic(void *k
 	local_flush_tlb_page(NULL, vaddr);
 #endif
 	pagefault_enable();
+	preempt_enable();
 }
 
 static inline struct page *kmap_atomic_to_page(void *ptr)

Re: PREEMPT_RT + HIGHMEM = segfaults during boot on ppc32

[Steve Rottinger]

Hi Thomas,

This patch solved my problem.

Thanks!

-Steve

Thomas Gleixner wrote:

> does the patch below help ?
>
> Thanks,
>
>	tglx
> ---
> Subject: powerpc-fixup-pagefault-disable-changes.patch
> From: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Date: Mon, 06 Jul 2009 17:36:01 +0200
>
> Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> ---
> arch/powerpc/include/asm/highmem.h |    3 +++
> 1 file changed, 3 insertions(+)
>
> Index: linux-2.6-tip/arch/powerpc/include/asm/highmem.h
> ===================================================================
> --- linux-2.6-tip.orig/arch/powerpc/include/asm/highmem.h
> +++ linux-2.6-tip/arch/powerpc/include/asm/highmem.h
> @@ -90,6 +90,7 @@ static inline void *kmap_atomic_prot(str
>  	unsigned long vaddr;
>
>  	/* even !CONFIG_PREEMPT needs this, for in_atomic in
> do_page_fault */
> +	preempt_disable();
> 	pagefault_disable();
> 	if (!PageHighMem(page))
> 		return page_address(page);
> @@ -118,6 +119,7 @@ static inline void kunmap_atomic(void *k
>
> 	if (vaddr < __fix_to_virt(FIX_KMAP_END)) {
> 		pagefault_enable();
> +		preempt_enable();
> 		return;
> 	}
>
> @@ -131,6 +133,7 @@ static inline void kunmap_atomic(void *k
>  	local_flush_tlb_page(NULL, vaddr);
>  #endif
> 	pagefault_enable();
> +	preempt_enable();
> }
>
> static inline struct page *kmap_atomic_to_page(void *ptr)