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-rw-r--r--arch/arm/mm/fault.c12
1 files changed, 11 insertions, 1 deletions
diff --git a/arch/arm/mm/fault.c b/arch/arm/mm/fault.c
index 0b6c4db44e0..4a884baf3b9 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);