From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-178.mta1.migadu.com (out-178.mta1.migadu.com [95.215.58.178]) (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 082C41F78E6 for ; Tue, 12 Aug 2025 04:40:12 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.178 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1754973614; cv=none; b=jZpqWnHwv9adG1aQ6DlV4s/iRRJyDvETvzqm2CDEvp1/UHB28Eoy1/U1/SgNbyl09elgoeogURwEfAXitAlHr5GLix8v4L25papUJN0G95FoiTC8P7Czo73KxTI8kID+E7FJPDZS+yESW7SCJb6eq9SzxtnbsilIk5tL/min2cU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1754973614; c=relaxed/simple; bh=7QEfWkMj0Q5U/6xWS27ArDIWZyu+E2DhnlE//zrVl8M=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=fWslUVnVoUzk4kyJpHtH75VpcrQJaWO2tmoRo8HhDRCg2w4qq8D/fN+dAXqST3FWQ8tBUy+5yAcEqLt9jiQKsjAB6wHgaV0vVqGCaPV69MMqCOvSvlqywcBihHKOh3MV06N5X3b2MRUbd3w4vgUi16954CZj4ZaVZo5ehWw97IM= 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=YPlU8LcF; arc=none smtp.client-ip=95.215.58.178 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="YPlU8LcF" Message-ID: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1754973601; 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=5SSuoYQxuP4N4+wD3+d2H9S35beJT6qelRadMcdDN44=; b=YPlU8LcFpadrQflSfXw2q6rECE/dUO5/8etQGdMlcPhxYeBkWoooqQT98Nh7B4lPctPdln Tl9sG5VZ6XQyNBthPJCFbmXuwGRe9GEB1pyKyW30s2YdDmTODsoZ8JpLWtC/+wQzbkD2lh Y42I9oje8XRVS9jS67f+Lv2CSc8XNns= Date: Mon, 11 Aug 2025 21:39:44 -0700 Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH RESEND v2 1/2] bpf: refactor max_depth computation in bpf_get_stack() Content-Language: en-GB To: Arnaud Lecomte 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> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Yonghong Song In-Reply-To: <20250809120911.88670-1-contact@arnaud-lcm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT 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;