From: Dima Zavin <d...@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)] Cc: <stable@vger.kernel.org> # 2.6.32+: 4542b6a0: ARM: 7365/1 Cc: <stable@vger.kernel.org> # 2.6.32+ Acked-by: Catalin Marinas <catalin.mari...@arm.com> Signed-off-by: Dima Zavin <d...@android.com> Signed-off-by: John Stultz <john.stu...@linaro.org> Signed-off-by: Will Deacon <will.dea...@arm.com> Signed-off-by: Russell King <rmk+ker...@arm.linux.org.uk> --- Greg: This patch is a candidate for -stable, but its dependency (listed above) wasn't marked as such, hence this retrospective submission. arch/arm/kernel/traps.c | 2 ++ 1 files changed, 2 insertions(+), 0 deletions(-) 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); } -- 1.7.4.1 -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html