From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) (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 D32AC1FBF6E; Tue, 12 Nov 2024 15:09:13 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=193.142.43.55 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1731424155; cv=none; b=lJkNECFZ+G675ErtVDgNPJfCEviJW5qJnxOHE5ECMcpYdPtxuq5i/ICd/t/xe5E372MCquHJoPRApWcft0JxeZU1+Xx+Em7dfPCBardp3LoW7nNh9NF2YIZik+40RfnwSadey7hkniknc1ucSZ1UBIweACWknDrAttdDxo3ti+A= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1731424155; c=relaxed/simple; bh=1yal8WnyDj7WFmQTjtVBqR/Cp2DayfFSKxcCh2gmJb4=; h=From:To:Cc:Subject:In-Reply-To:References:Date:Message-ID: MIME-Version:Content-Type; b=iirVO/SNFUIKvUp6qtd7n81n/qIg+WKMCJYlMAkuUdWKOnB7SnJ1UA40mgldV2rWjtyGIP9HCARTTV8GTml3nhv0YdlEeRamsg6BDO+c3i/KS0XwkE2WLwSvxQF6nLSGEiGBLsitj6HKYCa6N1982Qgufr+Q+hV3TgS/AlGhnr4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de; spf=pass smtp.mailfrom=linutronix.de; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=tSPx5jS9; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=p+/sOxN3; arc=none smtp.client-ip=193.142.43.55 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linutronix.de Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="tSPx5jS9"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="p+/sOxN3" From: Thomas Gleixner DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1731424152; 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: in-reply-to:in-reply-to:references:references; bh=+OwuircvxUSa0rTscRYfW7ivkxPcWV/LKtkFlw2hGKg=; b=tSPx5jS9oii0btPsjnoFzDrjL8q4vDgEm558vreVqWxdUWauz32a4YFHDA5Zm9DTWe/exO m/sFLgqyq0NaoM4ALjnXBvqKmkp2zFRxAIxBj3uAnInrZ4tCJ3ZDWZ/8wu8xYer7cdwS1i Vls7Bc+RMp2ybtDTFHdu5BQ0hgIzDVnLHprqxEkpmsN+YgklQyNfXSptRXteb20QKmgcxF bkEmEDJIyFIHzs3Rb5OxoXOcxV10phPPV69ZqtRiXVjUwzwFbwO6KprXIfuH+y5Xde8nn+ 5KkxYIg2zf5qdgTAWAw2rC+ZbzxkWSIYXrT+30Le8F2PMDud821tEcZxTcDuBQ== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1731424152; 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: in-reply-to:in-reply-to:references:references; bh=+OwuircvxUSa0rTscRYfW7ivkxPcWV/LKtkFlw2hGKg=; b=p+/sOxN3Bs0C7HUz9S8JdQpZDGBP1h0uNHRTlfS66d3H3AsogsfU6VQCumczuYdxB3dBdA 7de6h++tqZhrwmBg== To: Kunwu Chan , ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, martin.lau@linux.dev, eddyz87@gmail.com, song@kernel.org, yonghong.song@linux.dev, john.fastabend@gmail.com, kpsingh@kernel.org, sdf@fomichev.me, haoluo@google.com, jolsa@kernel.org, bigeasy@linutronix.de, clrkwllms@kernel.org, rostedt@goodmis.org Cc: bpf@vger.kernel.org, linux-kernel@vger.kernel.org, linux-rt-devel@lists.linux.dev, Kunwu Chan , syzbot+b506de56cbbb63148c33@syzkaller.appspotmail.com Subject: Re: [PATCH] bpf: Convert lpm_trie::lock to 'raw_spinlock_t' In-Reply-To: <20241108063214.578120-1-kunwu.chan@linux.dev> References: <20241108063214.578120-1-kunwu.chan@linux.dev> Date: Tue, 12 Nov 2024 16:08:47 +0100 Message-ID: <87v7wsmqv4.ffs@tglx> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain On Fri, Nov 08 2024 at 14:32, Kunwu Chan wrote: > When PREEMPT_RT is enabled, 'spinlock_t' becomes preemptible > and bpf program has owned a raw_spinlock under a interrupt handler, > which results in invalid lock acquire context. This explanation is just wrong. The problem has nothing to do with an interrupt handler. Interrupt handlers on RT kernels are force threaded. > __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline] > _raw_spin_lock_irqsave+0xd5/0x120 kernel/locking/spinlock.c:162 > trie_delete_elem+0x96/0x6a0 kernel/bpf/lpm_trie.c:462 > bpf_prog_2c29ac5cdc6b1842+0x43/0x47 > bpf_dispatcher_nop_func include/linux/bpf.h:1290 [inline] > __bpf_prog_run include/linux/filter.h:701 [inline] > bpf_prog_run include/linux/filter.h:708 [inline] > __bpf_trace_run kernel/trace/bpf_trace.c:2340 [inline] > bpf_trace_run1+0x2ca/0x520 kernel/trace/bpf_trace.c:2380 > trace_workqueue_activate_work+0x186/0x1f0 include/trace/events/workqueue.h:59 > __queue_work+0xc7b/0xf50 kernel/workqueue.c:2338 The problematic lock nesting is the work queue pool lock, which is a raw spinlock. > @@ -330,7 +330,7 @@ static long trie_update_elem(struct bpf_map *map, > if (key->prefixlen > trie->max_prefixlen) > return -EINVAL; > > - spin_lock_irqsave(&trie->lock, irq_flags); > + raw_spin_lock_irqsave(&trie->lock, irq_flags); > > /* Allocate and fill a new node */ Making this a raw spinlock moves the problem from the BPF trie code into the memory allocator. On RT the memory allocator cannot be invoked under a raw spinlock. Thanks, tglx