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 --- arch/sparc/mm/highmem.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) (limited to 'arch/sparc') diff --git a/arch/sparc/mm/highmem.c b/arch/sparc/mm/highmem.c index 5e50c09b7dc..4730eac0747 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); -- cgit v1.2.3-70-g09d2