From: "Alexei Starovoitov" <alexei.starovoitov@gmail.com>
To: "Ömer Mete Kaya" <omermetekaya0@gmail.com>, daniel@iogearbox.net
Cc: <john.fastabend@gmail.com>, <andrii@kernel.org>,
<eddyz87@gmail.com>, <memxor@gmail.com>, <martin.lau@linux.dev>,
<song@kernel.org>, <yonghong.song@linux.dev>, <jolsa@kernel.org>,
<emil@etsalapatis.com>, <ihor.solodrai@linux.dev>,
<bpf@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
<syzbot+fd7e415d891073b83e1f@syzkaller.appspotmail.com>
Subject: Re: [PATCH bpf] bpf: Fix smp_processor_id() warning in rhtab_delete_elem()
Date: Tue, 29 Sep 2026 06:09:44 +0000 [thread overview]
Message-ID: <DLRKRNCH0N6U.2CRAUPOWA8P2D@gmail.com> (raw)
In-Reply-To: <20260928173703.504474-1-omermetekaya0@gmail.com>
On Mon, Sep 28, 2026 at 08:31 PM Ömer Mete Kaya <omermetekaya0@gmail.com> wrote:
> bpf_mem_cache_free_rcu() uses this_cpu_ptr() which requires preemption
> to be disabled. In rhtab_delete_elem(), this call happens after
> bpf_enable_instrumentation(), so preemption is re-enabled at that
> point and this_cpu_ptr() triggers:
bpf_disable_instrumentation() doesn't disable preemption.
It's migrate_disable() plus bpf_prog_active++.
bpf_mem_alloc relies on the callers to disable migration.
See the comment above bpf_mem_alloc().
All callers of rhtab_delete_elem() do that except
__rhtab_map_lookup_and_delete_batch(). That's the bug.
bpf_disable_instrumentation() in rhtab_delete_elem() protects
the bucket lock from NMI progs. rhtab_map_update_elem() calls
bpf_mem_cache_alloc/free() outside of it too.
Don't stretch it. Disable migration in the batch.
> Fixes: 6905f8601298 ("bpf: Allow special fields in resizable hashtab")
Wrong tag. The batch came in
commit 818e00848227 ("bpf: Implement iteration ops for resizable hashtab")
pw-bot: cr
prev parent reply other threads:[~2026-09-29 6:09 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-09-28 17:31 Ömer Mete Kaya
2026-09-28 18:16 ` bot+bpf-ci
2026-09-29 6:09 ` Alexei Starovoitov [this message]
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