From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-187.mta1.migadu.com (out-187.mta1.migadu.com [95.215.58.187]) (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 6AF8A2F29 for ; Tue, 27 May 2025 05:34:10 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.187 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1748324052; cv=none; b=AOv9LBgXwbToI5srT7WasmfEj10zkI44Yyw0PRucZTCb69kPnfVS97/1P6FKeNIVw0kl3bVlV38wLVCxb8L4vQtlMlPJZ6vSBAwBC3O+/7ZEAC2n6MRTnntH0qNPWEV9ztQpAX1rkDY8aEAHFXZ+dOh+S2R9e+cJfwtHFKkH7oQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1748324052; c=relaxed/simple; bh=owmKOZ+LjHRRvTCtjxaqB/61XgX+EQg7MnF9vxRS2Cw=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=mAWIF1CX9zE6PFGHl7mcwSHjc6B2JaTy5mpbKqShcLzpWnkG6fy+5Ou0BjFY4bNMwN9a9gMXLFC9QmlkRAieRccq1B25s85EnI7U4Onbv+EM387N/qzZO16drmgMVHQCTB2Pc6GQZPvJeqo+BGmONMe3h66RepbfNPSdSrePX9M= 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=BPqGm6F3; arc=none smtp.client-ip=95.215.58.187 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="BPqGm6F3" Message-ID: <055a9abd-8137-4382-9830-551961cbcda2@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1748324048; 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=QtFxO4qrn8tZ4jKlC35uOPsc9iqCtcevGZOVYHd+UXs=; b=BPqGm6F3HWGvopIsRZJQ63ZQGlgUsEpMAm2AESEw7i90Q/7LnY2582ypHN8adZrQCmPfP2 9RU4HifVnQeGBb7d2YFtdXkZ/J03MWqoJSNklgycuazlNZ/295KpXuInPMs0Iv6YAmjUHp RRai0XHueLj1nmVKj5uVQx48zAlfT4k= Date: Tue, 27 May 2025 13:33:57 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [WARN] LOCKDEP: MAX_LOCKDEP_CHAIN_HLOCKS too low To: Waiman Long , peterz@infradead.org Cc: mingo@redhat.com, will@kernel.org, boqun.feng@gmail.com, linux-kernel@vger.kernel.org, Lance Yang , Zi Li References: <20250527020252.43684-1-lance.yang@linux.dev> Content-Language: en-US X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Lance Yang In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT Hi Longman, Thanks for looking into this! On 2025/5/27 12:48, Waiman Long wrote: > On 5/26/25 10:02 PM, Lance Yang wrote: >> From: Lance Yang >> >> Hi all, >> >> With CONFIG_LOCKDEP on, I got this warning during kernel builds: >> >> [Tue May 27 00:22:59 2025] BUG: MAX_LOCKDEP_CHAIN_HLOCKS too low! [...] >> >> $ cat .config|grep CONFIG_LOCKDEP >> CONFIG_LOCKDEP_SUPPORT=y >> CONFIG_LOCKDEP=y >> CONFIG_LOCKDEP_BITS=15 >> CONFIG_LOCKDEP_CHAINS_BITS=16 >> CONFIG_LOCKDEP_STACK_TRACE_BITS=19 >> CONFIG_LOCKDEP_STACK_TRACE_HASH_BITS=14 >> CONFIG_LOCKDEP_CIRCULAR_QUEUE_BITS=12 >> >> Is it safe? Or could this be a real locking issue? > > The lock chains store the locking order of nested locks. The default > value of 16 may be too low now as the kernel is becoming more complex in > term of possible nested locking orders. Anyway, I would suggest upping > the CONFIG_LOCKDEP_CHAIN_BITS to 17 or even 18 to prevent this kind of > problem. In fact, the latest RHEL debug kernel sets > CONFIG_LOCKDEP_CHAINS_BITS to 18. Yes, makes sense to me. Bumping it to 18 sounds reasonable as the kernel is getting more complex in terms of possible nested locking orders. It uses a bit more memory, but keeping LOCKDEP working is worth it ;) And if there are no objections, I’d be happy to send a patch making the change. Thanks, Lance > > Cheers, > Longman >