From 840ff6a4f6174d7fe19c206b5f36ff64123a2f45 Mon Sep 17 00:00:00 2001 From: Russell King Date: Tue, 20 Sep 2005 17:52:13 +0100 Subject: [PATCH] [ARM] Prevent deadlock in page fault handler As per x86, we may deadlock while trying to get the mmap semaphore. Implement the same fix, which allows (eg) recursive faults to cause an oops instead of deadlocking. Signed-off-by: Russell King --- arch/arm/mm/fault.c | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-) diff --git a/arch/arm/mm/fault.c b/arch/arm/mm/fault.c index 0b6c4db44e..4a884baf3b 100644 --- a/arch/arm/mm/fault.c +++ b/arch/arm/mm/fault.c @@ -233,7 +233,17 @@ do_page_fault(unsigned long addr, unsigned int fsr, struct pt_regs *regs) if (in_interrupt() || !mm) goto no_context; - down_read(&mm->mmap_sem); + /* + * As per x86, we may deadlock here. However, since the kernel only + * validly references user space from well defined areas of the code, + * we can bug out early if this is from code which shouldn't. + */ + if (!down_read_trylock(&mm->mmap_sem)) { + if (!user_mode(regs) && !search_exception_tables(regs->ARM_pc)) + goto no_context; + down_read(&mm->mmap_sem); + } + fault = __do_page_fault(mm, addr, fsr, tsk); up_read(&mm->mmap_sem); -- 2.39.5