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    Subject[ 54/55] ARM: 7409/1: Do not call flush_cache_user_range with mmap_sem held
    3.0-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    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: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    arch/arm/kernel/traps.c | 2 ++
    1 file changed, 2 insertions(+)

    --- a/arch/arm/kernel/traps.c
    +++ b/arch/arm/kernel/traps.c
    @@ -451,7 +451,9 @@ do_cache_op(unsigned long start, unsigne
    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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