From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from plesk.hostmyservers.fr (plesk.hostmyservers.fr [45.145.164.37]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id D4E23274B29; Tue, 12 Aug 2025 19:32:15 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=45.145.164.37 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1755027139; cv=none; b=V/1PJZ90etxaTU3E7lR/tKtzQVcH3pOEv1WFjIhoiFw9AbQ6W1RhQzVopsVr7npkWkLvowiyGYRWta+AGJsMuTb+nqmYCXbZxH2SWeSh2R7l1hBetcrjaAj/jYtQywD0lAO1mQPNLghCNo2ADl05m7PwwSHM4dhQrJG6WTMYWjE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1755027139; c=relaxed/simple; bh=sw/YuyXbj0SKwdTzogkSVkX70Y3N33Yy9MoAIY+BExE=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=lE8idhYFuYkNCaylHWzEYH7pxmbmlx6O1wwIEpw9jybf/kK4fscnX81sbfz9eR7j6qDO4cEP+H8/YhGgZhgpDMXPACS9iYLJZGQNBCxYY5TsAwhL1MeFu25pE9rA49z6Rp5a4eJT7eHK0e+f4Bdx/m1LBEAP7Q52PeEZD2kaHxk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=arnaud-lcm.com; spf=pass smtp.mailfrom=arnaud-lcm.com; arc=none smtp.client-ip=45.145.164.37 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=arnaud-lcm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arnaud-lcm.com Received: from [IPV6:2a02:8084:255b:aa00:acd6:d96f:40a0:aee] (unknown [IPv6:2a02:8084:255b:aa00:acd6:d96f:40a0:aee]) by plesk.hostmyservers.fr (Postfix) with ESMTPSA id ED80F4139D; Tue, 12 Aug 2025 19:32:12 +0000 (UTC) Authentication-Results: Plesk; spf=pass (sender IP is 2a02:8084:255b:aa00:acd6:d96f:40a0:aee) smtp.mailfrom=contact@arnaud-lcm.com smtp.helo=[IPV6:2a02:8084:255b:aa00:acd6:d96f:40a0:aee] Received-SPF: pass (Plesk: connection is authenticated) Message-ID: <084a70f2-96ef-43a1-a1d0-863496c4547e@arnaud-lcm.com> Date: Tue, 12 Aug 2025 20:32:11 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH RESEND v2 1/2] bpf: refactor max_depth computation in bpf_get_stack() To: Yonghong Song Cc: andrii@kernel.org, ast@kernel.org, bpf@vger.kernel.org, daniel@iogearbox.net, eddyz87@gmail.com, haoluo@google.com, john.fastabend@gmail.com, jolsa@kernel.org, kpsingh@kernel.org, linux-kernel@vger.kernel.org, martin.lau@linux.dev, sdf@fomichev.me, song@kernel.org, syzbot+c9b724fbb41cf2538b7b@syzkaller.appspotmail.com, syzkaller-bugs@googlegroups.com References: <20250809115833.87033-1-contact@arnaud-lcm.com> <20250809120911.88670-1-contact@arnaud-lcm.com> Content-Language: en-US From: Arnaud Lecomte In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-PPP-Message-ID: <175502713383.30733.7319759797711796805@Plesk> X-PPP-Vhost: arnaud-lcm.com Thanks Yonghong for your feedbacks and your patience ! On 12/08/2025 05:39, Yonghong Song wrote: > > > On 8/9/25 5:09 AM, Arnaud Lecomte wrote: >> A new helper function stack_map_calculate_max_depth() that >> computes the max depth for a stackmap. > > Please add 'bpf-next' in the subject like [PATCH bpf-next v2 1/2] > so CI can properly test the patch set. > >> >> Changes in v2: >>   - Removed the checking 'map_size % map_elem_size' from >> stack_map_calculate_max_depth >>   - Changed stack_map_calculate_max_depth params name to be more generic >> >> Signed-off-by: Arnaud Lecomte >> --- >>   kernel/bpf/stackmap.c | 30 ++++++++++++++++++++++++------ >>   1 file changed, 24 insertions(+), 6 deletions(-) >> >> diff --git a/kernel/bpf/stackmap.c b/kernel/bpf/stackmap.c >> index 3615c06b7dfa..532447606532 100644 >> --- a/kernel/bpf/stackmap.c >> +++ b/kernel/bpf/stackmap.c >> @@ -42,6 +42,27 @@ static inline int stack_map_data_size(struct >> bpf_map *map) >>           sizeof(struct bpf_stack_build_id) : sizeof(u64); >>   } >>   +/** >> + * stack_map_calculate_max_depth - Calculate maximum allowed stack >> trace depth >> + * @map_size:        Size of the buffer/map value in bytes > > let us rename 'map_size' to 'size' since the size represents size of > buffer or map, not just for map. > >> + * @elem_size:       Size of each stack trace element >> + * @flags:       BPF stack trace flags (BPF_F_USER_STACK, >> BPF_F_USER_BUILD_ID, ...) >> + * >> + * Return: Maximum number of stack trace entries that can be safely >> stored >> + */ >> +static u32 stack_map_calculate_max_depth(u32 map_size, u32 >> elem_size, u64 flags) > > map_size -> size > Also, you can replace 'flags' to 'skip', so below 'u32 skip = flags & > BPF_F_SKIP_FIELD_MASK' > is not necessary. > >> +{ >> +    u32 skip = flags & BPF_F_SKIP_FIELD_MASK; >> +    u32 max_depth; >> + >> +    max_depth = map_size / elem_size; >> +    max_depth += skip; >> +    if (max_depth > sysctl_perf_event_max_stack) >> +        return sysctl_perf_event_max_stack; >> + >> +    return max_depth; >> +} >> + >>   static int prealloc_elems_and_freelist(struct bpf_stack_map *smap) >>   { >>       u64 elem_size = sizeof(struct stack_map_bucket) + >> @@ -406,7 +427,7 @@ static long __bpf_get_stack(struct pt_regs *regs, >> struct task_struct *task, >>                   struct perf_callchain_entry *trace_in, >>                   void *buf, u32 size, u64 flags, bool may_fault) >>   { >> -    u32 trace_nr, copy_len, elem_size, num_elem, max_depth; >> +    u32 trace_nr, copy_len, elem_size, max_depth; >>       bool user_build_id = flags & BPF_F_USER_BUILD_ID; >>       bool crosstask = task && task != current; >>       u32 skip = flags & BPF_F_SKIP_FIELD_MASK; >> @@ -438,10 +459,7 @@ static long __bpf_get_stack(struct pt_regs >> *regs, struct task_struct *task, >>           goto clear; >>       } >>   -    num_elem = size / elem_size; >> -    max_depth = num_elem + skip; >> -    if (sysctl_perf_event_max_stack < max_depth) >> -        max_depth = sysctl_perf_event_max_stack; >> +    max_depth = stack_map_calculate_max_depth(size, elem_size, flags); >>         if (may_fault) >>           rcu_read_lock(); /* need RCU for perf's callchain below */ >> @@ -461,7 +479,7 @@ static long __bpf_get_stack(struct pt_regs *regs, >> struct task_struct *task, >>       } >>         trace_nr = trace->nr - skip; >> -    trace_nr = (trace_nr <= num_elem) ? trace_nr : num_elem; >> +    trace_nr = min(trace_nr, max_depth - skip); >>       copy_len = trace_nr * elem_size; >>         ips = trace->ip + skip; > >