linux-kernel - Re: [RFC v2 4/5] io_uring/bpf: add handle events callback

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <bf35d09b-e259-46b0-88d5-e950d9ced964@kernel.dk>
Date: Thu, 12 Jun 2025 08:07:26 -0600
From: Jens Axboe <axboe@...nel.dk>
To: Alexei Starovoitov <alexei.starovoitov@...il.com>,
 Pavel Begunkov <asml.silence@...il.com>
Cc: io-uring@...r.kernel.org, Martin KaFai Lau <martin.lau@...ux.dev>,
 bpf <bpf@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC v2 4/5] io_uring/bpf: add handle events callback

On 6/11/25 8:28 PM, Alexei Starovoitov wrote:
> On Fri, Jun 6, 2025 at 6:58?AM Pavel Begunkov <asml.silence@...il.com> wrote:
>>
>> +static inline int io_run_bpf(struct io_ring_ctx *ctx, struct iou_loop_state *state)
>> +{
>> +       scoped_guard(mutex, &ctx->uring_lock) {
>> +               if (!ctx->bpf_ops)
>> +                       return IOU_EVENTS_STOP;
>> +               return ctx->bpf_ops->handle_events(ctx, state);
>> +       }
>> +}
> 
> you're grabbing the mutex before calling bpf prog and doing
> it in a loop million times a second?
> Looks like massive overhead for program invocation.
> I'm surprised it's fast.

Grabbing a mutex is only expensive if it's contended, or obviously
if it's already held. Repeatedly grabbing it on submission where
submission is the only one expected to grab it (or off that path, at
least) means it should be very cheap.

-- 
Jens Axboe