On Tue 14-01-25 10:53:55, Peter Zijlstra wrote: > On Mon, Jan 13, 2025 at 06:19:17PM -0800, Alexei Starovoitov wrote: > > From: Alexei Starovoitov <ast@xxxxxxxxxx> > > > > Tracing BPF programs execute from tracepoints and kprobes where > > running context is unknown, but they need to request additional > > memory. > > > The prior workarounds were using pre-allocated memory and > > BPF specific freelists to satisfy such allocation requests. > > Instead, introduce gfpflags_allow_spinning() condition that signals > > to the allocator that running context is unknown. > > Then rely on percpu free list of pages to allocate a page. > > The rmqueue_pcplist() should be able to pop the page from. > > If it fails (due to IRQ re-entrancy or list being empty) then > > try_alloc_pages() attempts to spin_trylock zone->lock > > and refill percpu freelist as normal. > > > BPF program may execute with IRQs disabled and zone->lock is > > sleeping in RT, so trylock is the only option. > > how is spin_trylock() from IRQ context not utterly broken in RT? + if (IS_ENABLED(CONFIG_PREEMPT_RT) && (in_nmi() || in_hardirq())) + return NULL; Deals with that, right? -- Michal Hocko SUSE Labs
