From: Kumar Kartikeya Dwivedi <memxor@gmail.com>
To: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc: Martin KaFai Lau <kafai@fb.com>,
"David S. Miller" <davem@davemloft.net>,
Daniel Borkmann <daniel@iogearbox.net>,
Andrii Nakryiko <andrii@kernel.org>, Tejun Heo <tj@kernel.org>,
Delyan Kratunov <delyank@fb.com>, linux-mm <linux-mm@kvack.org>,
bpf <bpf@vger.kernel.org>, Kernel Team <kernel-team@fb.com>
Subject: Re: [PATCH v4 bpf-next 01/15] bpf: Introduce any context BPF specific memory allocator.
Date: Tue, 30 Aug 2022 00:59:39 +0200 [thread overview]
Message-ID: <CAP01T76qn=+WZ3jVb=ue=+Zf5FyKbdQy0b9KxExzK9SN_4DeBA@mail.gmail.com> (raw)
In-Reply-To: <CAADnVQLR4nBvJ0RpEdcGF1MFOW=MmA5xicofCyt8sP_AHMzAsA@mail.gmail.com>
On Tue, 30 Aug 2022 at 00:43, Alexei Starovoitov
<alexei.starovoitov@gmail.com> wrote:
>
> On Mon, Aug 29, 2022 at 3:39 PM Martin KaFai Lau <kafai@fb.com> wrote:
> >
> > On Thu, Aug 25, 2022 at 07:44:16PM -0700, Alexei Starovoitov wrote:
> > > +/* Mostly runs from irq_work except __init phase. */
> > > +static void alloc_bulk(struct bpf_mem_cache *c, int cnt, int node)
> > > +{
> > > + struct mem_cgroup *memcg = NULL, *old_memcg;
> > > + unsigned long flags;
> > > + void *obj;
> > > + int i;
> > > +
> > > + memcg = get_memcg(c);
> > > + old_memcg = set_active_memcg(memcg);
> > > + for (i = 0; i < cnt; i++) {
> > > + obj = __alloc(c, node);
> > > + if (!obj)
> > > + break;
> > > + if (IS_ENABLED(CONFIG_PREEMPT_RT))
> > > + /* In RT irq_work runs in per-cpu kthread, so disable
> > > + * interrupts to avoid preemption and interrupts and
> > > + * reduce the chance of bpf prog executing on this cpu
> > > + * when active counter is busy.
> > > + */
> > > + local_irq_save(flags);
> > > + if (local_inc_return(&c->active) == 1) {
> > Is it because it is always '== 1' here so that there is
> > no need to free the obj when it is '!= 1' ?
>
> Great catch. It's a bug indeed.
Is it a bug? It seems it will always be true for alloc_bulk. IIUC it
is only needed to prevent NMI's unit_alloc, unit_free touching
free_llist, so that NMI llist_adds atomically to free_llist_nmi
instead. Since this runs from irq_work, we run exclusive to other
unit_free, otherwise the __llist_add wouldn't be safe either.
unit_free already does local_irq_save.
next prev parent reply other threads:[~2022-08-29 23:00 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-08-26 2:44 [PATCH v4 bpf-next 00/15] bpf: " Alexei Starovoitov
2022-08-26 2:44 ` [PATCH v4 bpf-next 01/15] bpf: Introduce any context " Alexei Starovoitov
2022-08-29 21:30 ` Daniel Borkmann
2022-08-29 21:45 ` Alexei Starovoitov
2022-08-29 21:59 ` Daniel Borkmann
2022-08-29 22:04 ` Alexei Starovoitov
2022-08-29 22:39 ` Martin KaFai Lau
2022-08-29 22:42 ` Alexei Starovoitov
2022-08-29 22:59 ` Kumar Kartikeya Dwivedi [this message]
2022-08-29 23:13 ` Alexei Starovoitov
2022-08-26 2:44 ` [PATCH v4 bpf-next 02/15] bpf: Convert hash map to bpf_mem_alloc Alexei Starovoitov
2022-08-26 2:44 ` [PATCH v4 bpf-next 03/15] selftests/bpf: Improve test coverage of test_maps Alexei Starovoitov
2022-08-26 2:44 ` [PATCH v4 bpf-next 04/15] samples/bpf: Reduce syscall overhead in map_perf_test Alexei Starovoitov
2022-08-26 2:44 ` [PATCH v4 bpf-next 05/15] bpf: Relax the requirement to use preallocated hash maps in tracing progs Alexei Starovoitov
2022-08-26 2:44 ` [PATCH v4 bpf-next 06/15] bpf: Optimize element count in non-preallocated hash map Alexei Starovoitov
2022-08-29 21:47 ` Daniel Borkmann
2022-08-29 21:57 ` Alexei Starovoitov
2022-08-26 2:44 ` [PATCH v4 bpf-next 07/15] bpf: Optimize call_rcu " Alexei Starovoitov
2022-08-26 2:44 ` [PATCH v4 bpf-next 08/15] bpf: Adjust low/high watermarks in bpf_mem_cache Alexei Starovoitov
2022-08-26 2:44 ` [PATCH v4 bpf-next 09/15] bpf: Batch call_rcu callbacks instead of SLAB_TYPESAFE_BY_RCU Alexei Starovoitov
2022-08-26 2:44 ` [PATCH v4 bpf-next 10/15] bpf: Add percpu allocation support to bpf_mem_alloc Alexei Starovoitov
2022-08-26 2:44 ` [PATCH v4 bpf-next 11/15] bpf: Convert percpu hash map to per-cpu bpf_mem_alloc Alexei Starovoitov
2022-08-26 2:44 ` [PATCH v4 bpf-next 12/15] bpf: Remove tracing program restriction on map types Alexei Starovoitov
2022-08-26 2:44 ` [PATCH v4 bpf-next 13/15] bpf: Prepare bpf_mem_alloc to be used by sleepable bpf programs Alexei Starovoitov
2022-08-26 2:44 ` [PATCH v4 bpf-next 14/15] bpf: Remove prealloc-only restriction for " Alexei Starovoitov
2022-08-26 2:44 ` [PATCH v4 bpf-next 15/15] bpf: Introduce sysctl kernel.bpf_force_dyn_alloc Alexei Starovoitov
[not found] ` <f0e3e3ab-99b7-4d87-4b5a-b71ca7724310@iogearbox.net>
2022-08-29 22:27 ` Alexei Starovoitov
2022-08-27 16:57 ` [PATCH v4 bpf-next 00/15] bpf: BPF specific memory allocator Andrii Nakryiko
2022-08-27 22:53 ` Kumar Kartikeya Dwivedi
2022-08-29 15:47 ` Alexei Starovoitov
2022-09-09 20:10 ` Andrii Nakryiko
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