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Wed, 01 Jul 2026 01:05:35 -0700 (PDT) Date: Wed, 1 Jul 2026 08:05:23 +0000 From: Sechang Lim To: Alexei Starovoitov Cc: Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Paul Moore , John Fastabend , Martin KaFai Lau , Eduard Zingerman , Kumar Kartikeya Dwivedi , Song Liu , Yonghong Song , Jiri Olsa , bpf@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH bpf] bpf: move security_bpf_prog_free() out of RCU callback Message-ID: <3o66qg4u2op5x4qnqehhf52zctn4so62zqxk3ib4llfabc6ctx@gxnstpfvhqjf> References: <20260626093711.2969648-1-rhkrqnwk98@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline In-Reply-To: On Tue, Jun 30, 2026 at 04:17:26PM -0700, Alexei Starovoitov wrote: >On Fri Jun 26, 2026 at 2:37 AM PDT, Sechang Lim wrote: >> __bpf_prog_put_rcu() is the call_rcu() callback for non-sleepable programs. >> security_bpf_prog_free() called from there fires bpf_prog_free in softirq; >> if a sleepable LSM prog is attached to that hook, might_fault() BUGs: >> >> BUG: sleeping function called from invalid context >> in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 5038 >> preempt_count: 101, expected: 0 >> Call Trace: >> >> __bpf_prog_enter_sleepable+0x1cd/0x320 kernel/bpf/trampoline.c:1255 >> bpf_trampoline_6442549705+0x53/0xd7 >> security_bpf_prog_free+0xde/0x130 security/security.c:5465 >> __bpf_prog_put_rcu+0xab/0xd0 kernel/bpf/syscall.c:2365 >> rcu_do_batch kernel/rcu/tree.c:2617 [inline] >> handle_softirqs+0x236/0x800 kernel/softirq.c:622 >> >> >> The call_rcu/call_rcu_tasks_trace split reflects the freed program's >> sleepability, not that of any attached observer. >> >> Move security_bpf_prog_free() to __bpf_prog_put_noref() before the RCU >> deferral. >> >> Fixes: 1b67772e4e3f ("bpf,lsm: Refactor bpf_prog_alloc/bpf_prog_free LSM hooks") >> Signed-off-by: Sechang Lim >> --- >> kernel/bpf/syscall.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c >> index 630d530782fe..f14c3f0f8827 100644 >> --- a/kernel/bpf/syscall.c >> +++ b/kernel/bpf/syscall.c >> @@ -2362,7 +2362,6 @@ static void __bpf_prog_put_rcu(struct rcu_head *rcu) >> kvfree(aux->func_info); >> kfree(aux->func_info_aux); >> free_uid(aux->user); >> - security_bpf_prog_free(aux->prog); >> bpf_prog_free(aux->prog); >> } >> >> @@ -2378,6 +2377,7 @@ static void __bpf_prog_put_noref(struct bpf_prog *prog, bool deferred) >> if (prog->aux->attach_btf) >> btf_put(prog->aux->attach_btf); >> >> + security_bpf_prog_free(prog); > >I don't think you can just move it like that, since LSM side >may rely on RCU GP. >I think removing security_bpf_prog_free from sleepable is cleaner. > Ah, that sounds right. Will fix in v2. Thanks! Bests, Sechang