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Commit 20273941 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Linus Torvalds
Browse files

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: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
Reported-by: default avatarChristoph Hellwig <hch@infradead.org>
Acked-by: default avatarRik van Riel <riel@redhat.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent a8e23a29

arch/arm/mm/highmem.c

+2 −1
Original line number Diff line number Diff line
@@ -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)]));

arch/frv/mm/highmem.c

+2 −1
Original line number Diff line number Diff line
@@ -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);

arch/mips/mm/highmem.c

+2 −1
Original line number Diff line number Diff line
@@ -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);

arch/mn10300/include/asm/highmem.h

+3 −1
Original line number Diff line number Diff line
@@ -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__ */

arch/powerpc/mm/highmem.c

+3 −1
Original line number Diff line number Diff line
@@ -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);