From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-171.mta0.migadu.com (out-171.mta0.migadu.com [91.218.175.171]) (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 7956844AB68 for ; Tue, 4 Aug 2026 10:10:53 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.171 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785838256; cv=none; b=rGaSv/xdw31k5to+cgWNCVU0onFtK3zZTPj8Moxr7m70OJVaxnE5J+nrHZfGU6scUiVQDk018XMcuh79jqKe/xIrEKFYe/DDMUnvXne8jVrrmhHKYMyjvQe0Td928IPDcAbpXBvL9TsO6eU3l2vz77bP+jCCxY2QUt8QW28RLCg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785838256; c=relaxed/simple; bh=3LS7SmQMPn4ZNyRcndgHfU64Fewo90PTywg0Ik5GaOE=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=jVEl2ADoyhFcV3h9XosmWbby/jYPWTjMcfnd9sXeHzFPtCq6s6CQBAEHhpRnylE9UhIu8AJIiZ93fAg7VDc7kdjkBljiHkUNnyk64qHrhlS/IxCXNmMTNYB1G6mnOGWyDfK2slDVw3Szj4JNjrttR1ptjYquUfIJF5v+csKgBAY= 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=U4/3lqSu; arc=none smtp.client-ip=91.218.175.171 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="U4/3lqSu" Message-ID: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1785838251; 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=GqmXyZ+ydu7k847fTb4+bNha4IF2MJ31SeOi++fTq9E=; b=U4/3lqSufnDD0WS5sbifzBSyaHsEbf5BNCXi/uyqz6hi+Xna/FK0CQnOcM3ZhkLu83pTr3 R3Hw8XFVfgc4di7forFSx9gLSZcWAXTpa/uTd1w8jWWaEbHDv6GkHSxQydN3qcwir9Ml9+ o08Az9uXAV9mqbmBmG42P/TBbx0veh0= Date: Tue, 4 Aug 2026 18:09:58 +0800 Precedence: bulk X-Mailing-List: bpf@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: Kumar Kartikeya Dwivedi , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Eduard Zingerman , 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> <4aa061ed-6640-42b4-9f12-e33edb8ba1b2@linux.dev> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Kaitao Cheng In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT 在 2026/8/4 17:42, Kumar Kartikeya Dwivedi 写道: > On Tue Aug 4, 2026 at 11:37 AM CEST, Kaitao Cheng wrote: >> 在 2026/8/4 16:43, Kumar Kartikeya Dwivedi 写道: >>> On Tue Aug 4, 2026 at 10:32 AM CEST, 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. >>>> >>>> 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; >>> >>> Why not apply it to all of the existing kfuncs? Also, use [PATCH bpf-next] subject. >> >> I do not think all kfuncs are suitable for the KF_SPIN_LOCK context. >> Kfuncs marked with KF_SLEEPABLE are an obvious example. Developers >> should add KF_SPIN_LOCK with great care and ensure that the kfunc >> does not sleep and is safe to call in atomic context; otherwise, it >> could easily introduce deadlocks. >> >> However, the kfuncs explicitly allowed by kfunc_spin_allowed(), such >> as those covered by is_bpf_graph_api_kfunc, is_bpf_iter_num_api_kfunc, >> is_bpf_res_spin_lock_kfunc, is_bpf_arena_kfunc and is_bpf_stream_kfunc, >> can be marked with KF_SPIN_LOCK. We can then simplify kfunc_spin_allowed() >> to rely solely on the flag. > > Yes, of course. I meant those that we maintain as a list in the verifier. > KF_SPIN_LOCK is not a very optimal name. Should we do KF_ALLOWED_IN_LOCK_CS? > A bit verbose but better captures the intended meaning. The existing KF_* flag names are generally concise, so a much longer name feels somewhat out of place. I would also prefer the name to preserve the full spin_lock semantics, since "lock" can refer to many different lock types, such as mutex. Alternatively, following the naming of GFP_ATOMIC, could we call it KF_ATOMIC? -- Thanks Kaitao Cheng