linux-kernel - Re: 2.6.25-rc7-git2: Reported regressions from 2.6.24

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Date:	Fri, 28 Mar 2008 11:47:34 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	penberg@...helsinki.fi, clameter@....com, rjw@...k.pl,
	pstaszewski@...com.pl, linux-kernel@...r.kernel.org,
	bunk@...nel.org, protasnb@...il.com
Subject: Re: 2.6.25-rc7-git2: Reported regressions from 2.6.24

On Fri, 28 Mar 2008 11:20:52 -0700 (PDT)
Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> The code in question is __slab_alloc().

The bug we're discussing is http://bugzilla.kernel.org/show_bug.cgi?id=10318

It's a driver call stright into the page allocator - slab is not involved.

I was planning on plugging it this way:


From: Andrew Morton <akpm@...ux-foundation.org>

I believe http://bugzilla.kernel.org/show_bug.cgi?id=10318 is a false
positive.  There's no way in which networking will be using highmem pages
here, so it won't be taking the KM_USER0 kmap slot, so there's no point in
performing these checks.

Cc: Pawel Staszewski <pstaszewski@...com.pl>
Cc: Ingo Molnar <mingo@...e.hu>
Cc: Christoph Lameter <clameter@....com>
Cc: "David S. Miller" <davem@...emloft.net>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
---

 arch/x86/mm/highmem_32.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff -puN arch/x86/mm/highmem_32.c~x86-kmap_atomic-debugging-only-run-debug_kmap_atomic_prot-for-highmem-pages arch/x86/mm/highmem_32.c
--- a/arch/x86/mm/highmem_32.c~x86-kmap_atomic-debugging-only-run-debug_kmap_atomic_prot-for-highmem-pages
+++ a/arch/x86/mm/highmem_32.c
@@ -73,15 +73,15 @@ void *kmap_atomic_prot(struct page *page
 {
 	enum fixed_addresses idx;
 	unsigned long vaddr;
-	/* even !CONFIG_PREEMPT needs this, for in_atomic in do_page_fault */
-
-	debug_kmap_atomic_prot(type);
 
+	/* even !CONFIG_PREEMPT needs this, for in_atomic in do_page_fault */
 	pagefault_disable();
 
 	if (!PageHighMem(page))
 		return page_address(page);
 
+	debug_kmap_atomic_prot(type);
+
 	idx = type + KM_TYPE_NR*smp_processor_id();
 	vaddr = __fix_to_virt(FIX_KMAP_BEGIN + idx);
 	BUG_ON(!pte_none(*(kmap_pte-idx)));
_

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