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authorPeter Zijlstra <a.p.zijlstra@chello.nl>2010-10-27 22:32:58 (GMT)
committerLinus Torvalds <torvalds@linux-foundation.org>2010-10-28 01:03:05 (GMT)
commit20273941f2129aa5a432796d98a276ed73d60782 (patch)
tree85da0d951ac10f239f81ad7f69559fdeb692095b /arch/sparc/mm
parenta8e23a291852cd7c4fb5ca696dbb93912185ad10 (diff)
downloadlinux-20273941f2129aa5a432796d98a276ed73d60782.tar.xz
mm: fix race in kunmap_atomic()
Christoph reported a nice splat which illustrated a race in the new stack based kmap_atomic implementation. The problem is that we pop our stack slot before we're completely done resetting its state -- in particular clearing the PTE (sometimes that's CONFIG_DEBUG_HIGHMEM). If an interrupt happens before we actually clear the PTE used for the last slot, that interrupt can reuse the slot in a dirty state, which triggers a BUG in kmap_atomic(). Fix this by introducing kmap_atomic_idx() which reports the current slot index without actually releasing it and use that to find the PTE and delay the _pop() until after we're completely done. Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Reported-by: Christoph Hellwig <hch@infradead.org> Acked-by: Rik van Riel <riel@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'arch/sparc/mm')
-rw-r--r--arch/sparc/mm/highmem.c4
1 files changed, 3 insertions, 1 deletions
diff --git a/arch/sparc/mm/highmem.c b/arch/sparc/mm/highmem.c
index 5e50c09..4730eac 100644
--- a/arch/sparc/mm/highmem.c
+++ b/arch/sparc/mm/highmem.c
@@ -75,7 +75,7 @@ void __kunmap_atomic(void *kvaddr)
return;
}
- type = kmap_atomic_idx_pop();
+ type = kmap_atomic_idx();
#ifdef CONFIG_DEBUG_HIGHMEM
{
@@ -104,6 +104,8 @@ void __kunmap_atomic(void *kvaddr)
#endif
}
#endif
+
+ kmap_atomic_idx_pop();
pagefault_enable();
}
EXPORT_SYMBOL(__kunmap_atomic);