| Date | Mon, 28 May 2012 04:13:16 +0100 | From | Ben Hutchings <> | Subject | [ 074/117] ARM: 7409/1: Do not call flush_cache_user_range with mmap_sem held |
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3.2-stable review patch. If anyone has any objections, please let me know.
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From: Dima Zavin <dima@android.com>
commit 435a7ef52db7d86e67a009b36cac1457f8972391 upstream.
We can't be holding the mmap_sem while calling flush_cache_user_range because the flush can fault. If we fault on a user address, the page fault handler will try to take mmap_sem again. Since both places acquire the read lock, most of the time it succeeds. However, if another thread tries to acquire the write lock on the mmap_sem (e.g. mmap) in between the call to flush_cache_user_range and the fault, the down_read in do_page_fault will deadlock.
[will: removed drop of vma parameter as already queued by rmk (7365/1)]
Acked-by: Catalin Marinas <catalin.marinas@arm.com> Signed-off-by: Dima Zavin <dima@android.com> Signed-off-by: John Stultz <john.stultz@linaro.org> Signed-off-by: Will Deacon <will.deacon@arm.com> Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk> Signed-off-by: Ben Hutchings <ben@decadent.org.uk> --- arch/arm/kernel/traps.c | 2 ++ 1 file changed, 2 insertions(+)
diff --git a/arch/arm/kernel/traps.c b/arch/arm/kernel/traps.c index 55b2f3d..63d402f 100644 --- a/arch/arm/kernel/traps.c +++ b/arch/arm/kernel/traps.c @@ -496,7 +496,9 @@ do_cache_op(unsigned long start, unsigned long end, int flags) if (end > vma->vm_end) end = vma->vm_end; + up_read(&mm->mmap_sem); flush_cache_user_range(start, end); + return; } up_read(&mm->mmap_sem); }
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