From: Roman Gushchin <roman.gushchin@linux.dev>
To: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc: bpf <bpf@vger.kernel.org>, linux-mm <linux-mm@kvack.org>,
LKML <linux-kernel@vger.kernel.org>,
JP Kobryn <inwardvessel@gmail.com>,
Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Shakeel Butt <shakeel.butt@linux.dev>,
Michal Hocko <mhocko@kernel.org>,
Johannes Weiner <hannes@cmpxchg.org>
Subject: Re: [PATCH bpf-next v3 4/6] mm: introduce BPF kfuncs to access memcg statistics and events
Date: Mon, 22 Dec 2025 19:09:14 -0800 [thread overview]
Message-ID: <87ms39c2sl.fsf@linux.dev> (raw)
In-Reply-To: <CAADnVQJ_WLMRXYV5p4Lk2+nxdC01iAaKQhYecMjx4rXdBeXjNw@mail.gmail.com> (Alexei Starovoitov's message of "Mon, 22 Dec 2025 16:11:19 -1000")
Alexei Starovoitov <alexei.starovoitov@gmail.com> writes:
> On Mon, Dec 22, 2025 at 12:18 PM Roman Gushchin
> <roman.gushchin@linux.dev> wrote:
>>
>> + if (idx < 0 || idx >= MEMCG_NR_STAT || !memcg_stat_item_valid(idx))
>> + return (unsigned long)-1;
>
> memcg_stat_item_valid() and memcg_stat_item_valid()
> helpers introduced specifically to be used in these kfuncs,
> so I feel it's cleaner to do all idx checking within them
> instead of splitting the checks like this.
> Then it will be easier to see that
> memcg_stat_item_valid(idx) access is in bounds when idx < MEMCG_NR_STAT
>
> Also I'd do one check like (u32)idx >= MEMCG_NR_STAT
> and drop idx < 0 part. Compiler is probably smart enough to
> optimize this way itself, but I'd still do one check.
Sure, good point.
Thanks for reviews!
next prev parent reply other threads:[~2025-12-23 3:09 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-12-22 22:17 [PATCH bpf-next v3 0/6] mm: bpf kfuncs to access memcg data Roman Gushchin
2025-12-22 22:17 ` [PATCH bpf-next v3 1/6] mm: declare memcg_page_state_output() in memcontrol.h Roman Gushchin
2025-12-22 22:17 ` [PATCH bpf-next v3 2/6] mm: introduce BPF kfuncs to deal with memcg pointers Roman Gushchin
2025-12-22 22:17 ` [PATCH bpf-next v3 3/6] mm: introduce bpf_get_root_mem_cgroup() BPF kfunc Roman Gushchin
2025-12-22 22:17 ` [PATCH bpf-next v3 4/6] mm: introduce BPF kfuncs to access memcg statistics and events Roman Gushchin
2025-12-23 2:11 ` Alexei Starovoitov
2025-12-23 3:09 ` Roman Gushchin [this message]
2025-12-22 22:17 ` [PATCH bpf-next v3 5/6] bpf: selftests: selftests for memcg stat kfuncs Roman Gushchin
2025-12-22 22:17 ` [PATCH bpf-next v3 6/6] MAINTAINERS: add an entry for MM BPF extensions Roman Gushchin
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