From: Eduard Zingerman <eddyz87@gmail.com>
To: Emil Tsalapatis <emil@etsalapatis.com>
Cc: bpf@vger.kernel.org, ast@kernel.org, daniel@iogearbox.net,
andrii@kernel.org
Subject: Re: [PATCH 1/2] bpf: Allow bpf_for/bpf_repeat calls while holding a spinlock
Date: Sat, 04 Jan 2025 16:11:53 -0800 [thread overview]
Message-ID: <fbc6c684c4d374a3b7b08198bf4778c05963a313.camel@gmail.com> (raw)
In-Reply-To: <CABFh=a66Fk70ipHbrq+Jh-hA33vHq0fOJd+R9=1tRA1t212CzQ@mail.gmail.com>
On Sat, 2025-01-04 at 14:25 -0500, Emil Tsalapatis wrote:
[...]
> > > @@ -19048,7 +19066,7 @@ static int do_check(struct bpf_verifier_env *env)
> > > if (env->cur_state->active_locks) {
> > > if ((insn->src_reg == BPF_REG_0 && insn->imm != BPF_FUNC_spin_unlock) ||
> > > (insn->src_reg == BPF_PSEUDO_KFUNC_CALL &&
> > > - (insn->off != 0 || !is_bpf_graph_api_kfunc(insn->imm)))) {
> > > + (insn->off != 0 || !kfunc_spin_allowed(insn->imm)))) {
> > > verbose(env, "function calls are not allowed while holding a lock\n");
> > > return -EINVAL;
> > > }
> >
> >
> > Nit: technically, 'bpf_loop' is a helper function independent of iter_num API.
> > I suggest to change the name to is_bpf_iter_num_api_kfunc.
> > Also, if we decide that loops are ok with spin locks,
> > the condition above should be adjusted to allow calls to bpf_loop,
> > e.g. to make the following test work:
> >
>
> (Sorry for the duplicate, accidentally didn't send the email in plaintext)
>
> Will do, bpf_iter_num_api_kfunc is more reasonable. For bpf_loops
> AFAICT we would need to ensure the callback cannot sleep,
> which would need extra checks/changes to the verifier compared to
> bpf_for. IMO we can deal with it in a separate patch if we think
> allowing it is a good idea.
Not really, callbacks are verified "in-line". When a function call to
a function calling synchronous callback is verified, verifier steps
into callback body some number of times. If a sleeping call would
be discovered during callback function verification, verifier would
see that spin lock is currently taken and report error. So, this is
really just a check for particular helper call.
[...]
next prev parent reply other threads:[~2025-01-05 0:11 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-01-01 20:37 [PATCH 0/2] bpf: Allow bpf_for/bpf_repeat while holding spin Emil Tsalapatis
2025-01-01 20:37 ` [PATCH 1/2] bpf: Allow bpf_for/bpf_repeat calls while holding a spinlock Emil Tsalapatis
2025-01-02 18:02 ` Eduard Zingerman
2025-01-04 19:25 ` Emil Tsalapatis
2025-01-05 0:11 ` Eduard Zingerman [this message]
2025-01-06 14:56 ` Emil Tsalapatis
2025-01-06 18:59 ` Alexei Starovoitov
2025-01-01 20:37 ` [PATCH 2/2] selftests/bpf: test bpf_for within spin lock section Emil Tsalapatis
2025-01-02 18:05 ` Eduard Zingerman
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