From: Sebastian Andrzej Siewior > Sent: 16 October 2018 21:25 > I've seen the WARN_ON_ONCE(__read_cr3() != build_cr3()) in > switch_mm_irqs_off() every once in a while during a snapshotted system > upgrade. > I also saw the warning early during which was introduced in commit > decab0888e6e ("x86/mm: Remove preempt_disable/enable() from > __native_flush_tlb()"). The callchain is > > get_page_from_freelist() -> post_alloc_hook() -> __kernel_map_pages() > > with CONFIG_DEBUG_PAGEALLOC enabled. > > Turns out, once I disable preemption around __flush_tlb_all() both > warnings do not appear. > > Disable preemption during CR3 reset / __flush_tlb_all(). > > Fixes: decab0888e6e ("x86/mm: Remove preempt_disable/enable() from > __native_flush_tlb()") > Signed-off-by: Sebastian Andrzej Siewior <bige...@linutronix.de> > --- > arch/x86/mm/pageattr.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c > index 51a5a69ecac9f..fe6b21f0a6631 100644 > --- a/arch/x86/mm/pageattr.c > +++ b/arch/x86/mm/pageattr.c > @@ -2088,7 +2088,9 @@ void __kernel_map_pages(struct page *page, int > numpages, int enable) > * We should perform an IPI and flush all tlbs, > * but that can deadlock->flush only current cpu: > */ > + preempt_disable(); > __flush_tlb_all(); > + preempt_enable();
Can it make any sense to flush the tlb with preemption enabled? Surely preemption must be disabled over something else as well? David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)