On Sat, Aug 15, 2020 at 10:42:50AM +0200, Peter Zijlstra wrote: > On Sat, Aug 15, 2020 at 01:14:53AM +0200, Thomas Gleixner wrote: > > > #1 trivial fix is to force switching to an high prio thread or a soft > > interrupt which does the allocation > > Yeah, push the alocation out to another context. I did consider it, but > why bother? > > Also, raising a softirq can't be done from every context, that's a whole > new problem. You can do irq_work I suppose, but not all architectures > support the self-IPI yet. > > All in all, it's just more complexity than the fairly trivial > __alloc_page_lockless(). > > Whichever way around, we can't rely on the allocation. One way to enforce that would be to put something like this at the beginning of the __alloc_page_lockless() function: if (IS_ENABLED(CONFIG_PROVE_LOCKING) && (prandom_u32() & 0xffff)) return NULL; I am sure that there is a better choice than CONFIG_PROVE_LOCKING. But whatever the choice, there is nothing quite like the occasional allocation failure during testing to convince people that such failure really can happen. Thanx, Paul
