Update from upstream with manual merge of Yasunori Goto's

changes to swiotlb.c made in commit 281dd25cdc0d6903929b79183816d151ea626341
since this file has been moved from arch/ia64/lib/swiotlb.c to
lib/swiotlb.c

Signed-off-by: Tony Luck <tony.luck@intel.com>

1 files changed, 11 insertions, 1 deletions

diff --git a/arch/arm/mm/fault.c b/arch/arm/mm/fault.c
index 0b6c4db44e08..4a884baf3b9c 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);