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authorPeter Zijlstra <a.p.zijlstra@chello.nl>2010-10-27 15:32:58 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2010-10-27 18:03:05 -0700
commit20273941f2129aa5a432796d98a276ed73d60782 (patch)
tree85da0d951ac10f239f81ad7f69559fdeb692095b /include/linux/highmem.h
parenta8e23a291852cd7c4fb5ca696dbb93912185ad10 (diff)
downloadop-kernel-dev-20273941f2129aa5a432796d98a276ed73d60782.zip
op-kernel-dev-20273941f2129aa5a432796d98a276ed73d60782.tar.gz
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 'include/linux/highmem.h')
-rw-r--r--include/linux/highmem.h5
1 files changed, 5 insertions, 0 deletions
diff --git a/include/linux/highmem.h b/include/linux/highmem.h
index 102f76b..e913819 100644
--- a/include/linux/highmem.h
+++ b/include/linux/highmem.h
@@ -88,6 +88,11 @@ static inline int kmap_atomic_idx_push(void)
return idx;
}
+static inline int kmap_atomic_idx(void)
+{
+ return __get_cpu_var(__kmap_atomic_idx) - 1;
+}
+
static inline int kmap_atomic_idx_pop(void)
{
int idx = --__get_cpu_var(__kmap_atomic_idx);
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