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[ARM] Prevent deadlock in page fault handler

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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>
This commit is contained in:
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);