From mboxrd@z Thu Jan 1 00:00:00 1970 From: will.deacon@arm.com (Will Deacon) Date: Fri, 25 May 2012 15:38:04 +0100 Subject: [STABLE PATCH] ARM: 7409/1: Do not call flush_cache_user_range with mmap_sem held Message-ID: <1337956684-23569-1-git-send-email-will.deacon@arm.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org From: Dima Zavin 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: # 2.6.32+: 4542b6a0: ARM: 7365/1 Cc: # 2.6.32+ Acked-by: Catalin Marinas Signed-off-by: Dima Zavin Signed-off-by: John Stultz Signed-off-by: Will Deacon Signed-off-by: Russell King --- 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