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/x86/mm/iomap_32.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) (limited to 'arch/x86/mm/iomap_32.c') diff --git a/arch/x86/mm/iomap_32.c b/arch/x86/mm/iomap_32.c index 75a3d7f24a2c..7b179b499fa3 100644 --- a/arch/x86/mm/iomap_32.c +++ b/arch/x86/mm/iomap_32.c @@ -98,7 +98,7 @@ iounmap_atomic(void __iomem *kvaddr) vaddr <= __fix_to_virt(FIX_KMAP_BEGIN)) { int idx, type; - type = kmap_atomic_idx_pop(); + type = kmap_atomic_idx(); idx = type + KM_TYPE_NR * smp_processor_id(); #ifdef CONFIG_DEBUG_HIGHMEM @@ -111,6 +111,7 @@ iounmap_atomic(void __iomem *kvaddr) * attributes or becomes a protected page in a hypervisor. */ kpte_clear_flush(kmap_pte-idx, vaddr); + kmap_atomic_idx_pop(); } pagefault_enable(); -- cgit v1.2.3