| Message ID | 20240416-bpf_wq-v1-17-c9e66092f842@kernel.org (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | Introduce bpf_wq | expand |
On Tue, Apr 16, 2024 at 04:08:30PM +0200, Benjamin Tissoires wrote: > again, copy/paste from bpf_timer_start(). > > Signed-off-by: Benjamin Tissoires <bentiss@kernel.org> > --- > kernel/bpf/helpers.c | 24 ++++++++++++++++++++++++ > 1 file changed, 24 insertions(+) > > diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c > index e5c8adc44619..ed5309a37eda 100644 > --- a/kernel/bpf/helpers.c > +++ b/kernel/bpf/helpers.c > @@ -2728,6 +2728,29 @@ __bpf_kfunc int bpf_wq_init(struct bpf_wq *wq, void *map, unsigned int flags) > return __bpf_async_init(async, map, flags, BPF_ASYNC_TYPE_WQ); > } > > +__bpf_kfunc int bpf_wq_start(struct bpf_wq *wq, unsigned int flags) > +{ > + struct bpf_async_kern *async = (struct bpf_async_kern *)wq; > + struct bpf_work *w; > + int ret = 0; > + > + if (in_nmi()) > + return -EOPNOTSUPP; > + if (flags) > + return -EINVAL; > + __bpf_spin_lock_irqsave(&async->lock); > + w = async->work; > + if (!w || !w->cb.prog) { > + ret = -EINVAL; > + goto out; > + } > + > + schedule_work(&w->work); > +out: > + __bpf_spin_unlock_irqrestore(&async->lock); Looks like you're not adding wq_cancel kfunc in this patch set and it's probably a good thing not to expose async cancel to bpf users, since it's a foot gun. Even when we eventually add wq_cancel_sync kfunc it will not be removing a callback. So we can drop spinlock here. READ_ONCE of w and cb would be enough. Since they cannot get back to NULL once init-ed and cb is set.
On Apr 18 2024, Alexei Starovoitov wrote: > On Tue, Apr 16, 2024 at 04:08:30PM +0200, Benjamin Tissoires wrote: > > again, copy/paste from bpf_timer_start(). > > > > Signed-off-by: Benjamin Tissoires <bentiss@kernel.org> > > --- > > kernel/bpf/helpers.c | 24 ++++++++++++++++++++++++ > > 1 file changed, 24 insertions(+) > > > > diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c > > index e5c8adc44619..ed5309a37eda 100644 > > --- a/kernel/bpf/helpers.c > > +++ b/kernel/bpf/helpers.c > > @@ -2728,6 +2728,29 @@ __bpf_kfunc int bpf_wq_init(struct bpf_wq *wq, void *map, unsigned int flags) > > return __bpf_async_init(async, map, flags, BPF_ASYNC_TYPE_WQ); > > } > > > > +__bpf_kfunc int bpf_wq_start(struct bpf_wq *wq, unsigned int flags) > > +{ > > + struct bpf_async_kern *async = (struct bpf_async_kern *)wq; > > + struct bpf_work *w; > > + int ret = 0; > > + > > + if (in_nmi()) > > + return -EOPNOTSUPP; > > + if (flags) > > + return -EINVAL; > > + __bpf_spin_lock_irqsave(&async->lock); > > + w = async->work; > > + if (!w || !w->cb.prog) { > > + ret = -EINVAL; > > + goto out; > > + } > > + > > + schedule_work(&w->work); > > +out: > > + __bpf_spin_unlock_irqrestore(&async->lock); > > Looks like you're not adding wq_cancel kfunc in this patch set and > it's probably a good thing not to expose async cancel to bpf users, > since it's a foot gun. Honestly I just felt the patch series was big enough for a PoC and comparison with sleepable bpf_timer. But if we think this needs not to be added, I guess that works too :) > Even when we eventually add wq_cancel_sync kfunc it will not be > removing a callback. Yeah, I understood that bit :) > So we can drop spinlock here. > READ_ONCE of w and cb would be enough. > Since they cannot get back to NULL once init-ed and cb is set. Great, thanks for the review (and the other patches). I'll work toward v2. Cheers, Benjamin
On Fri, Apr 19, 2024 at 8:14 AM Benjamin Tissoires <bentiss@kernel.org> wrote: > > > Honestly I just felt the patch series was big enough for a PoC and > comparison with sleepable bpf_timer. But if we think this needs not to > be added, I guess that works too :) It certainly did its job to compare the two and imo bpf_wq with kfunc approach looks cleaner overall and will be easier to extend in the long term. I mean that we'll be adding 3 kfuncs initially: bpf_wq_init, bpf_wq_start, bpf_wq_set_callback. imo that's good enough to land it and get some exposure. I'll be using it right away to refactor bpf_arena_alloc.h into actual arena allocator for bpf progs that is not just a selftest. I'm currently working on locks for bpf_arena. Kumar has a patch set that adds bpf_preempt_disble kfunc and coupled with bpf_wq we'll have all mechanisms to build arbitrary data structures/algorithms as bpf programs.
On Apr 19 2024, Alexei Starovoitov wrote: > On Fri, Apr 19, 2024 at 8:14 AM Benjamin Tissoires <bentiss@kernel.org> wrote: > > > > > > Honestly I just felt the patch series was big enough for a PoC and > > comparison with sleepable bpf_timer. But if we think this needs not to > > be added, I guess that works too :) > > It certainly did its job to compare the two and imo bpf_wq with kfunc approach > looks cleaner overall and will be easier to extend in the long term. Yeah. I agree. I'm also glad we pick the bpf_wq approach as I gave it a lot more care :) Talking about extending, I think I'll need delayed_work soon enough. Most of the time when I receive an input event, the device is preventing any communication with it, and with plain bpf_wq, it's likely that when the code kicks in the device won't have processed the current input, meaning to a useless retry. With delayed_works, I can schedule it slightly later, and have a higher chance of not having to retry. I've got a quick hack locally that I can submit once this series get merged. > > I mean that we'll be adding 3 kfuncs initially: > bpf_wq_init, bpf_wq_start, bpf_wq_set_callback. > > imo that's good enough to land it and get some exposure. sounds good to me. > I'll be using it right away to refactor bpf_arena_alloc.h into > actual arena allocator for bpf progs that is not just a selftest. > > I'm currently working on locks for bpf_arena. > Kumar has a patch set that adds bpf_preempt_disble kfunc and > coupled with bpf_wq we'll have all mechanisms to build > arbitrary data structures/algorithms as bpf programs. Oh. I did not realize that it was that needed for outside of my playground. That's good to hear :) Cheers, Benjamin
diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c index e5c8adc44619..ed5309a37eda 100644 --- a/kernel/bpf/helpers.c +++ b/kernel/bpf/helpers.c @@ -2728,6 +2728,29 @@ __bpf_kfunc int bpf_wq_init(struct bpf_wq *wq, void *map, unsigned int flags) return __bpf_async_init(async, map, flags, BPF_ASYNC_TYPE_WQ); } +__bpf_kfunc int bpf_wq_start(struct bpf_wq *wq, unsigned int flags) +{ + struct bpf_async_kern *async = (struct bpf_async_kern *)wq; + struct bpf_work *w; + int ret = 0; + + if (in_nmi()) + return -EOPNOTSUPP; + if (flags) + return -EINVAL; + __bpf_spin_lock_irqsave(&async->lock); + w = async->work; + if (!w || !w->cb.prog) { + ret = -EINVAL; + goto out; + } + + schedule_work(&w->work); +out: + __bpf_spin_unlock_irqrestore(&async->lock); + return ret; +} + __bpf_kfunc int bpf_wq_set_callback_impl(struct bpf_wq *wq, int (callback_fn)(void *map, int *key, struct bpf_wq *wq), unsigned int flags__k, @@ -2821,6 +2844,7 @@ BTF_ID_FLAGS(func, bpf_dynptr_clone) BTF_ID_FLAGS(func, bpf_modify_return_test_tp) BTF_ID_FLAGS(func, bpf_wq_init) BTF_ID_FLAGS(func, bpf_wq_set_callback_impl) +BTF_ID_FLAGS(func, bpf_wq_start) BTF_KFUNCS_END(common_btf_ids) static const struct btf_kfunc_id_set common_kfunc_set = {
again, copy/paste from bpf_timer_start(). Signed-off-by: Benjamin Tissoires <bentiss@kernel.org> --- kernel/bpf/helpers.c | 24 ++++++++++++++++++++++++ 1 file changed, 24 insertions(+)