On Fri, Nov 21, 2014 at 08:38:07AM -0800, Andy Lutomirski wrote: > On Nov 21, 2014 8:27 AM, "Tejun Heo" <t...@kernel.org> wrote: > > > > Hello, Andy. > > > > On Thu, Nov 20, 2014 at 03:55:09PM -0800, Andy Lutomirski wrote: > > > That doesn't appear to have anything to with nmi though, right? > > > > I thought that was the main offender but, apparently, not any more. > > > > > Wouldn't this issue be fixed by moving the vmalloc_fault check into > > > do_page_fault before exception_enter? > > > > Can you please elaborate why that'd fix the issue? I'm not > > intimiately familiar with the fault handling so it'd be great if you > > can give me some pointers in terms of where to look at. > > do_page_fault is called directly from asm. It does: > > prev_state = exception_enter(); > __do_page_fault(regs, error_code, address); > exception_exit(prev_state); > > The vmalloc fixup is in __do_page_fault. > > exception_enter does various accounting and tracing things, and I > think that the recursion in stack trace I saw was in exception_enter. > > If you move the vmalloc fixup before exception_enter() and return if > the fault was from vmalloc, then you can't recurse. You need to be > careful not to touch anything that uses RCU before exception_enter, > though.
That fixes the exception_enter() recursion but surely more issues with per cpu memory faults are lurking somewhere now or in the future. I'm going to add recursion protection to user_exit()/user_enter() anyway. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
