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>
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@ -89,7 +89,7 @@ void __kunmap_atomic(void *kvaddr)
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int idx, type;
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if (kvaddr >= (void *)FIXADDR_START) {
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type = kmap_atomic_idx_pop();
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type = kmap_atomic_idx();
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idx = type + KM_TYPE_NR * smp_processor_id();
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if (cache_is_vivt())
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@ -101,6 +101,7 @@ void __kunmap_atomic(void *kvaddr)
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#else
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(void) idx; /* to kill a warning */
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#endif
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kmap_atomic_idx_pop();
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} else if (vaddr >= PKMAP_ADDR(0) && vaddr < PKMAP_ADDR(LAST_PKMAP)) {
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/* this address was obtained through kmap_high_get() */
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kunmap_high(pte_page(pkmap_page_table[PKMAP_NR(vaddr)]));
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@ -68,7 +68,7 @@ EXPORT_SYMBOL(__kmap_atomic);
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void __kunmap_atomic(void *kvaddr)
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{
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int type = kmap_atomic_idx_pop();
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int type = kmap_atomic_idx();
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switch (type) {
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case 0: __kunmap_atomic_primary(4, 6); break;
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case 1: __kunmap_atomic_primary(5, 7); break;
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@ -83,6 +83,7 @@ void __kunmap_atomic(void *kvaddr)
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default:
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BUG();
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}
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kmap_atomic_idx_pop();
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pagefault_enable();
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}
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EXPORT_SYMBOL(__kunmap_atomic);
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@ -74,7 +74,7 @@ void __kunmap_atomic(void *kvaddr)
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return;
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}
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type = kmap_atomic_idx_pop();
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type = kmap_atomic_idx();
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#ifdef CONFIG_DEBUG_HIGHMEM
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{
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int idx = type + KM_TYPE_NR * smp_processor_id();
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@ -89,6 +89,7 @@ void __kunmap_atomic(void *kvaddr)
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local_flush_tlb_one(vaddr);
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}
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#endif
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kmap_atomic_idx_pop();
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pagefault_enable();
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}
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EXPORT_SYMBOL(__kunmap_atomic);
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@ -101,7 +101,7 @@ static inline void __kunmap_atomic(unsigned long vaddr)
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return;
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}
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type = kmap_atomic_idx_pop();
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type = kmap_atomic_idx();
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#if HIGHMEM_DEBUG
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{
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@ -119,6 +119,8 @@ static inline void __kunmap_atomic(unsigned long vaddr)
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__flush_tlb_one(vaddr);
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}
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#endif
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kmap_atomic_idx_pop();
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pagefault_enable();
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}
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#endif /* __KERNEL__ */
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@ -62,7 +62,7 @@ void __kunmap_atomic(void *kvaddr)
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return;
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}
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type = kmap_atomic_idx_pop();
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type = kmap_atomic_idx();
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#ifdef CONFIG_DEBUG_HIGHMEM
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{
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@ -79,6 +79,8 @@ void __kunmap_atomic(void *kvaddr)
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local_flush_tlb_page(NULL, vaddr);
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}
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#endif
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kmap_atomic_idx_pop();
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pagefault_enable();
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}
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EXPORT_SYMBOL(__kunmap_atomic);
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@ -75,7 +75,7 @@ void __kunmap_atomic(void *kvaddr)
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return;
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}
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type = kmap_atomic_idx_pop();
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type = kmap_atomic_idx();
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#ifdef CONFIG_DEBUG_HIGHMEM
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{
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@ -104,6 +104,8 @@ void __kunmap_atomic(void *kvaddr)
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#endif
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}
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#endif
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kmap_atomic_idx_pop();
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pagefault_enable();
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}
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EXPORT_SYMBOL(__kunmap_atomic);
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@ -241,7 +241,7 @@ void __kunmap_atomic(void *kvaddr)
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pte_t pteval = *pte;
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int idx, type;
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type = kmap_atomic_idx_pop();
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type = kmap_atomic_idx();
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idx = type + KM_TYPE_NR*smp_processor_id();
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/*
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@ -252,6 +252,7 @@ void __kunmap_atomic(void *kvaddr)
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BUG_ON(!pte_present(pteval) && !pte_migrating(pteval));
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kmap_atomic_unregister(pte_page(pteval), vaddr);
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kpte_clear_flush(pte, vaddr);
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kmap_atomic_idx_pop();
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} else {
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/* Must be a lowmem page */
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BUG_ON(vaddr < PAGE_OFFSET);
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@ -74,7 +74,7 @@ void __kunmap_atomic(void *kvaddr)
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vaddr <= __fix_to_virt(FIX_KMAP_BEGIN)) {
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int idx, type;
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type = kmap_atomic_idx_pop();
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type = kmap_atomic_idx();
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idx = type + KM_TYPE_NR * smp_processor_id();
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#ifdef CONFIG_DEBUG_HIGHMEM
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@ -87,6 +87,7 @@ void __kunmap_atomic(void *kvaddr)
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* attributes or becomes a protected page in a hypervisor.
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*/
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kpte_clear_flush(kmap_pte-idx, vaddr);
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kmap_atomic_idx_pop();
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}
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#ifdef CONFIG_DEBUG_HIGHMEM
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else {
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@ -98,7 +98,7 @@ iounmap_atomic(void __iomem *kvaddr)
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vaddr <= __fix_to_virt(FIX_KMAP_BEGIN)) {
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int idx, type;
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type = kmap_atomic_idx_pop();
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type = kmap_atomic_idx();
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idx = type + KM_TYPE_NR * smp_processor_id();
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#ifdef CONFIG_DEBUG_HIGHMEM
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@ -111,6 +111,7 @@ iounmap_atomic(void __iomem *kvaddr)
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* attributes or becomes a protected page in a hypervisor.
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*/
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kpte_clear_flush(kmap_pte-idx, vaddr);
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kmap_atomic_idx_pop();
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}
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pagefault_enable();
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@ -88,6 +88,11 @@ static inline int kmap_atomic_idx_push(void)
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return idx;
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}
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static inline int kmap_atomic_idx(void)
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{
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return __get_cpu_var(__kmap_atomic_idx) - 1;
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}
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static inline int kmap_atomic_idx_pop(void)
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{
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int idx = --__get_cpu_var(__kmap_atomic_idx);
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