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From bf1dbf3f545a79e9ac5ff460053283f2760f095b Mon Sep 17 00:00:00 2001
From: Dima Zavin <dima@android.com>
Date: Mon, 30 Apr 2012 10:26:14 +0100
Subject: [PATCH 073/117] ARM: 7409/1: Do not call flush_cache_user_range with
mmap_sem held
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 f363ad9..160cb16 100644
--- a/arch/arm/kernel/traps.c
+++ b/arch/arm/kernel/traps.c
@@ -488,7 +488,9 @@ 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);
}
--
1.7.9.5
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