From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-179.mta0.migadu.com (out-179.mta0.migadu.com [91.218.175.179]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id EE0693E63AE for ; Tue, 4 Aug 2026 09:16:31 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.179 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785834994; cv=none; b=mPFQvfmbF7aehdptFhDBRlmrpeorVRyIrfIGkAd2SDT5kLVT1zcF9EZdqePdGmJqBaT6IVkWqmk3OOY8PVHcxgRET7hYofAla4v9SN4qOpGC9gPRCaro+AqHuBwbUFvBd/STevc8NTBkKz843QOBohSZ5Wi3lc4Hx3W2CRJ4vuk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785834994; c=relaxed/simple; bh=4RnfTQVjVWJQ4mE5NBYc9aWk8W1gF/iUjTd0tcdfm4U=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=XAJE0FeOpJ3KinDbMrHeiVSdvgOqaqexufhl9CtUphlbEOP7ij11JtbJOXZD+eRlGURXfXf4NkV9gPSlxR9PBSCRsVJnT5hz8G9oY7ZSTbIRAS6zFYa0Z6UVw3rbod92a8RqRPmpO7bZpVZnzT17aL6UX3PBef183RdkeOuI0BM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=NdCR7OZT; arc=none smtp.client-ip=91.218.175.179 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="NdCR7OZT" Message-ID: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1785834989; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=d7WVS9+Dj1aYQt4n8Wp3bUj42/l8lW+B2HDlbRvzazE=; b=NdCR7OZTZLrUtL4NmxOGPkDTeYYjesw833waZosaz8i/8gIYwsQlqCk1/Iu29ogwIKLQQq mmwK0ZR7INhQFEoeuMqjUYaUZmrJXVj4YHstHNv+oFi3tTKUywPbjdOE4+EBwTmJHbtism oT4VePPoh9Btc12hpIojIhQdkTf4tDA= Date: Tue, 4 Aug 2026 17:15:39 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH] bpf: add KF_SPIN_LOCK flag for kfuncs under bpf_spin_lock To: Kaitao Cheng , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Eduard Zingerman , Kumar Kartikeya Dwivedi , Martin KaFai Lau , Song Liu , Yonghong Song , Jiri Olsa , Emil Tsalapatis , John Fastabend , Ihor Solodrai Cc: bpf@vger.kernel.org, linux-kernel@vger.kernel.org, Kaitao Cheng References: <20260804083212.79271-1-kaitao.cheng@linux.dev> Content-Language: en-US X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Leon Hwang In-Reply-To: <20260804083212.79271-1-kaitao.cheng@linux.dev> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT [PATCH bpf-next] bpf: ... On 4/8/26 16:32, Kaitao Cheng wrote: > From: Kaitao Cheng > > Introduce the KF_SPIN_LOCK kfunc metadata flag in BTF so kfuncs may be > explicitly marked as safe to call while holding bpf_spin_lock. > > Allow kfuncs defined in kernel modules to be marked with KF_SPIN_LOCK. Sounds reasonable to me. I did see the requirement when implementing a custom struct_ops. A selftest is required for this new flag. Thanks, Leon > > Example: BTF_ID_FLAGS(func, $kfunc_name, KF_SPIN_LOCK) > > Signed-off-by: Kaitao Cheng > --- > include/linux/btf.h | 1 + > kernel/bpf/verifier.c | 20 +++++++++++++++----- > 2 files changed, 16 insertions(+), 5 deletions(-) > > diff --git a/include/linux/btf.h b/include/linux/btf.h > index c09b7994de4e..380dc10b6750 100644 > --- a/include/linux/btf.h > +++ b/include/linux/btf.h > @@ -79,6 +79,7 @@ > #define KF_ARENA_ARG1 (1 << 14) /* kfunc takes an arena pointer as its first argument */ > #define KF_ARENA_ARG2 (1 << 15) /* kfunc takes an arena pointer as its second argument */ > #define KF_IMPLICIT_ARGS (1 << 16) /* kfunc has implicit arguments supplied by the verifier */ > +#define KF_SPIN_LOCK (1 << 17) /* kfunc is allowed inside bpf_spin_lock-ed region */ > > /* > * Tag marking a kernel function as a kfunc. This is meant to minimize the > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c > index 7aa47342dc65..9f3feba3c2fe 100644 > --- a/kernel/bpf/verifier.c > +++ b/kernel/bpf/verifier.c > @@ -11657,11 +11657,21 @@ static bool is_bpf_stream_kfunc(u32 btf_id) > btf_id == special_kfunc_list[KF_bpf_stream_print_stack]; > } > > -static bool kfunc_spin_allowed(u32 btf_id) > +static bool kfunc_spin_allowed(struct bpf_verifier_env *env, s32 func_id, s16 offset) > { > - return is_bpf_graph_api_kfunc(btf_id) || is_bpf_iter_num_api_kfunc(btf_id) || > - is_bpf_res_spin_lock_kfunc(btf_id) || is_bpf_arena_kfunc(btf_id) || > - is_bpf_stream_kfunc(btf_id); > + struct bpf_kfunc_meta kfunc; > + int err; > + > + if (is_bpf_graph_api_kfunc(func_id) || is_bpf_iter_num_api_kfunc(func_id) || > + is_bpf_res_spin_lock_kfunc(func_id) || is_bpf_arena_kfunc(func_id) || > + is_bpf_stream_kfunc(func_id)) > + return true; > + > + err = fetch_kfunc_meta(env, func_id, offset, &kfunc); > + if (err || !kfunc.flags) > + return false; > + > + return *kfunc.flags & KF_SPIN_LOCK; > } > > static bool is_sync_callback_calling_kfunc(u32 btf_id) > @@ -17289,7 +17299,7 @@ static int do_check_insn(struct bpf_verifier_env *env, bool *do_print_state) > insn->imm != BPF_FUNC_spin_unlock && > insn->imm != BPF_FUNC_kptr_xchg) || > (insn->src_reg == BPF_PSEUDO_KFUNC_CALL && > - (insn->off != 0 || !kfunc_spin_allowed(insn->imm)))) { > + !kfunc_spin_allowed(env, insn->imm, insn->off))) { > verbose(env, > "function calls are not allowed while holding a lock\n"); > return -EINVAL;