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? It can lead to try to priority boost the idle thread, among other crazy things.
