[STABLE PATCH] ARM: 7409/1: Do not call flush_cache_user_range with mmap_sem held
Will Deacon
will.deacon at arm.com
Fri May 25 10:38:04 EDT 2012
From: Dima Zavin <dima at 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 at vger.kernel.org> # 2.6.32+: 4542b6a0: ARM: 7365/1
Cc: <stable at vger.kernel.org> # 2.6.32+
Acked-by: Catalin Marinas <catalin.marinas at arm.com>
Signed-off-by: Dima Zavin <dima at android.com>
Signed-off-by: John Stultz <john.stultz at linaro.org>
Signed-off-by: Will Deacon <will.deacon at arm.com>
Signed-off-by: Russell King <rmk+kernel at 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
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