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>

9 files changed, 21 insertions, 9 deletions

diff --git a/arch/arm/mm/highmem.c b/arch/arm/mm/highmem.c
index c00f119babb..c435fd9e1da 100644
--- a/arch/arm/mm/highmem.c
+++ b/arch/arm/mm/highmem.c
@@ -89,7 +89,7 @@ void __kunmap_atomic(void *kvaddr)
         int idx, type;
 
         if (kvaddr >= (void *)FIXADDR_START) {
-                type = kmap_atomic_idx_pop();
+                type = kmap_atomic_idx();
                 idx = type + KM_TYPE_NR * smp_processor_id();
 
                 if (cache_is_vivt())
@@ -101,6 +101,7 @@ void __kunmap_atomic(void *kvaddr)
 #else
                 (void) idx;  /* to kill a warning */
 #endif
+                kmap_atomic_idx_pop();
         } else if (vaddr >= PKMAP_ADDR(0) && vaddr < PKMAP_ADDR(LAST_PKMAP)) {
                 /* this address was obtained through kmap_high_get() */
                 kunmap_high(pte_page(pkmap_page_table[PKMAP_NR(vaddr)]));
diff --git a/arch/frv/mm/highmem.c b/arch/frv/mm/highmem.c
index 61088dcc159..fd7fcd4c2e3 100644
--- a/arch/frv/mm/highmem.c
+++ b/arch/frv/mm/highmem.c
@@ -68,7 +68,7 @@ EXPORT_SYMBOL(__kmap_atomic);
 
 void __kunmap_atomic(void *kvaddr)
 {
-        int type = kmap_atomic_idx_pop();
+        int type = kmap_atomic_idx();
         switch (type) {
         case 0:         __kunmap_atomic_primary(4, 6);  break;
         case 1:         __kunmap_atomic_primary(5, 7);  break;
@@ -83,6 +83,7 @@ void __kunmap_atomic(void *kvaddr)
         default:
                 BUG();
         }
+        kmap_atomic_idx_pop();
         pagefault_enable();
 }
 EXPORT_SYMBOL(__kunmap_atomic);
diff --git a/arch/mips/mm/highmem.c b/arch/mips/mm/highmem.c
index 1e69b1fb4b8..3634c7ea06a 100644
--- a/arch/mips/mm/highmem.c
+++ b/arch/mips/mm/highmem.c
@@ -74,7 +74,7 @@ void __kunmap_atomic(void *kvaddr)
                 return;
         }
 
-        type = kmap_atomic_idx_pop();
+        type = kmap_atomic_idx();
 #ifdef CONFIG_DEBUG_HIGHMEM
         {
                 int idx = type + KM_TYPE_NR * smp_processor_id();
@@ -89,6 +89,7 @@ void __kunmap_atomic(void *kvaddr)
                 local_flush_tlb_one(vaddr);
         }
 #endif
+        kmap_atomic_idx_pop();
         pagefault_enable();
 }
 EXPORT_SYMBOL(__kunmap_atomic);
diff --git a/arch/mn10300/include/asm/highmem.h b/arch/mn10300/include/asm/highmem.h
index f577ba2268c..e2155e68645 100644
--- a/arch/mn10300/include/asm/highmem.h
+++ b/arch/mn10300/include/asm/highmem.h
@@ -101,7 +101,7 @@ static inline void __kunmap_atomic(unsigned long vaddr)
                 return;
         }
 
-        type = kmap_atomic_idx_pop();
+        type = kmap_atomic_idx();
 
 #if HIGHMEM_DEBUG
         {
@@ -119,6 +119,8 @@ static inline void __kunmap_atomic(unsigned long vaddr)
                 __flush_tlb_one(vaddr);
         }
 #endif
+
+        kmap_atomic_idx_pop();
         pagefault_enable();
 }
 #endif /* __KERNEL__ */
diff --git a/arch/powerpc/mm/highmem.c b/arch/powerpc/mm/highmem.c
index b0848b462bb..e7450bdbe83 100644
--- a/arch/powerpc/mm/highmem.c
+++ b/arch/powerpc/mm/highmem.c
@@ -62,7 +62,7 @@ void __kunmap_atomic(void *kvaddr)
                 return;
         }
 
-        type = kmap_atomic_idx_pop();
+        type = kmap_atomic_idx();
 
 #ifdef CONFIG_DEBUG_HIGHMEM
         {
@@ -79,6 +79,8 @@ void __kunmap_atomic(void *kvaddr)
                 local_flush_tlb_page(NULL, vaddr);
         }
 #endif
+
+        kmap_atomic_idx_pop();
         pagefault_enable();
 }
 EXPORT_SYMBOL(__kunmap_atomic);
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);
diff --git a/arch/tile/mm/highmem.c b/arch/tile/mm/highmem.c
index 8ef6595e162..abb57331cf6 100644
--- a/arch/tile/mm/highmem.c
+++ b/arch/tile/mm/highmem.c
@@ -241,7 +241,7 @@ void __kunmap_atomic(void *kvaddr)
                 pte_t pteval = *pte;
                 int idx, type;
 
-                type = kmap_atomic_idx_pop();
+                type = kmap_atomic_idx();
                 idx = type + KM_TYPE_NR*smp_processor_id();
 
                 /*
@@ -252,6 +252,7 @@ void __kunmap_atomic(void *kvaddr)
                 BUG_ON(!pte_present(pteval) && !pte_migrating(pteval));
                 kmap_atomic_unregister(pte_page(pteval), vaddr);
                 kpte_clear_flush(pte, vaddr);
+                kmap_atomic_idx_pop();
         } else {
                 /* Must be a lowmem page */
                 BUG_ON(vaddr < PAGE_OFFSET);
diff --git a/arch/x86/mm/highmem_32.c b/arch/x86/mm/highmem_32.c
index d723e369003..b4996266210 100644
--- a/arch/x86/mm/highmem_32.c
+++ b/arch/x86/mm/highmem_32.c
@@ -74,7 +74,7 @@ void __kunmap_atomic(void *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
@@ -87,6 +87,7 @@ void __kunmap_atomic(void *kvaddr)
                  * attributes or becomes a protected page in a hypervisor.
                  */
                 kpte_clear_flush(kmap_pte-idx, vaddr);
+                kmap_atomic_idx_pop();
         }
 #ifdef CONFIG_DEBUG_HIGHMEM
         else {
diff --git a/arch/x86/mm/iomap_32.c b/arch/x86/mm/iomap_32.c
index 75a3d7f24a2..7b179b499fa 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();