From 20273941f2129aa5a432796d98a276ed73d60782 Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Wed, 27 Oct 2010 15:32:58 -0700 Subject: 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 Reported-by: Christoph Hellwig Acked-by: Rik van Riel Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/highmem.h | 5 +++++ 1 file changed, 5 insertions(+) (limited to 'include') diff --git a/include/linux/highmem.h b/include/linux/highmem.h index 102f76be90d..e9138198e82 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); -- cgit v1.2.3