Messages in this thread | | | Subject | Re: PFs on pages pinned with get_user_pages() | From | Peter Zijlstra <> | Date | Thu, 29 Jan 2009 15:52:37 +0100 |
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On Thu, 2009-01-29 at 15:41 +0100, Frank Mehnert wrote: > On Thursday 29 January 2009, Peter Zijlstra wrote: > > On Thu, 2009-01-29 at 15:02 +0100, Frank Mehnert wrote: > > > I'm one of the VirtualBox developers. We are trying to fix the annoying > > > kerneloops warning 'BUG: sleeping function called from invalid context' > > > reported by the Fedora folks. This warning occurs when do_swap_page() > > > calls lock_page() and in_atomic() returns true. > > > > > > This warning appears when we touch into memory which is pinned with > > > get_user_pages(). In VT-x/AMD-V mode we are executing some code in the > > > context of the Linux kernel. To prevent scheduling of the current CPU > > > core we disable the interripts. preempt_disable() would be probably the > > > better choice but this would oops as well if CONFIG_PREEMPT is enabled. > > > > but to get there, you'd have to have called handle_mm_fault() which > > requires the mmap_sem, which should also give that might_sleep() > > warning. > > The stacktrace is > > __might_sleep() > lock_page() > handle_mm_fault() > do_page_fault() > error_code > > So yes, handle_mm_fault() is called. But I assume that down_read_trylock() > succeeded before we were forced to call down_read(). > > > That aside, is there any reason you have to avoid scheduling? Otherwise > > I would just allow so and be done with it. > > The reason is that our code expects that to ensure syncing of the CPU > state with the saved state. I fear it is quite difficult to change that...
Ah, is that what KVM uses the preempt notifiers for? Could you too?
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