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[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 <rmk+kernel@arm.linux.org.uk>
hifive-unleashed-5.1
Russell King 2005-09-20 17:52:13 +01:00 committed by Russell King
parent 5fe10ab190
commit 840ff6a4f6
1 changed files with 11 additions and 1 deletions
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12
arch/arm/mm/fault.c
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@ -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);