From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) (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 1E57179CE for ; Wed, 26 Jun 2024 00:39:06 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.129.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1719362348; cv=none; b=gLSAzvTIupDHNn4ynam+z+NF7tauwS74g49PE3oqXBj3qv8I/UDnZGLEuKXIxXZm4HThhOj9yliWnYI4MRaHFhKzuqTXxN5pvHkDSLp5C1nUS5oV4iKdKsubEqzpwBnQjC8I0nolTcryuTt3o7PmoFgN7xdKAIjd/dnGIvsUJCI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1719362348; c=relaxed/simple; bh=vph3snsBVbClZGIZjxHgwbgS1GlkN+zSDa1EVBnWpbQ=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=XEFXpPxAfbJUyC+wLBs0QjqMkGc51vRmQLhMDoBxyS19mkMuUpCspzEX75GhMabYlmn7nAZpAYXgsqTEp+SzJ15ltZXW1hhS5bpvDEdc+DlbUiOksaf5HEMwDa81skVu1GWtwuho5V+0KSGk3M5vbErynpiIXwOuIn6x/5EwoTk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=eRWwrH+T; arc=none smtp.client-ip=170.10.129.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="eRWwrH+T" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1719362346; 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=m7cosekoPKXkwrvYHFRpUSibVa04zhxh3op5EgjNV2M=; b=eRWwrH+TL69cofXtP9qbkfuft55T8GgtN2Bi449Y8A43mUuOYuBk8ry2UkZ7oGNN/g7Zz9 JCdlLiyl42O2XagHiJ1Ja0Ye50t+dg5MSlbEQ/njaRMl1qgxiAOgxlSoXMX6gSs55wbuzf fFJPE0okuCeHX7ZdA/ZJccbJvEZzAaE= Received: from mx-prod-mc-03.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-487-69KgG4rkNx2VmvWPFkVUAQ-1; Tue, 25 Jun 2024 20:39:03 -0400 X-MC-Unique: 69KgG4rkNx2VmvWPFkVUAQ-1 Received: from mx-prod-int-04.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-04.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.40]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 54DA419560B2; Wed, 26 Jun 2024 00:39:02 +0000 (UTC) Received: from localhost (unknown [10.72.116.8]) by mx-prod-int-04.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id E4B381956087; Wed, 26 Jun 2024 00:39:00 +0000 (UTC) Date: Wed, 26 Jun 2024 08:38:56 +0800 From: Baoquan He To: Uladzislau Rezki Cc: Nick Bowler , Hailong Liu , linux-kernel@vger.kernel.org, Linux regressions mailing list , linux-mm@kvack.org, sparclinux@vger.kernel.org, Andrew Morton Subject: Re: PROBLEM: kernel crashes when running xfsdump since ~6.4 Message-ID: References: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Scanned-By: MIMEDefang 3.0 on 10.30.177.40 On 06/25/24 at 10:05pm, Uladzislau Rezki wrote: > > > > > > /** > > > > > > * cpumask_next - get the next cpu in a cpumask > > > > > > * @n: the cpu prior to the place to search (i.e. return will be > @n) > > > > > > * @srcp: the cpumask pointer > > > > > > * > > > > > > * Return: >= nr_cpu_ids if no further cpus set. > > > > > > > > > > Ah, I got what you mean. In the vbq case, it may not have chance to get > > > > > a return number as nr_cpu_ids. Becuase the hashed index limits the > > > > > range to [0, nr_cpu_ids-1], and cpu_possible(index) will guarantee it > > > > > won't be the highest cpu number [nr_cpu_ids-1] since CPU[nr_cpu_ids-1] must > > > > > be possible CPU. > > > > > > > > > > Do I miss some corner cases? > > > > > > > > > Right. We guarantee that a highest CPU is available by doing: % nr_cpu_ids. > > > > So we do not need to use *next_wrap() variant. You do not miss anything :) > > > > > > > > Hailong Liu has proposed more simpler version: > > > > > > > > > > > > diff --git a/mm/vmalloc.c b/mm/vmalloc.c > > > > index 11fe5ea208aa..e1e63ffb9c57 100644 > > > > --- a/mm/vmalloc.c > > > > +++ b/mm/vmalloc.c > > > > @@ -1994,8 +1994,9 @@ static struct xarray * > > > > addr_to_vb_xa(unsigned long addr) > > > > { > > > > int index = (addr / VMAP_BLOCK_SIZE) % num_possible_cpus(); > > > > + int cpu = cpumask_nth(index, cpu_possible_mask); > > > > > > > > - return &per_cpu(vmap_block_queue, index).vmap_blocks; > > > > + return &per_cpu(vmap_block_queue, cpu).vmap_blocks; > > > > > > > > > > > > which just takes a next CPU if an index is not set in the cpu_possible_mask. > > > > > > > > The only thing that can be updated in the patch is to replace num_possible_cpu() > > > > by the nr_cpu_ids. > > > > > > > > Any thoughts? I think we need to fix it by a minor change so it is > > > > easier to back-port on stable kernels. > > > > > > Yeah, sounds good since the regresson commit is merged in v6.3. > > > Please feel free to post this and the hash array patch separately for > > > formal reviewing. > > > > > Agreed! The patch about hash array i will post later. > > > > > By the way, when I am replying this mail, I check the cpumask_nth() > > > again. I doubt it may take more checking then cpu_possible(), given most > > > of systems don't have gaps in cpu_possible_mask. I could be dizzy at > > > this moment. > > > > > > static inline unsigned int cpumask_nth(unsigned int cpu, const struct cpumask *srcp) > > > { > > > return find_nth_bit(cpumask_bits(srcp), small_cpumask_bits, cpumask_check(cpu)); > > > } > > > > > Yep, i do not think it is a big problem based on your noted fact. > > > Checked. There is a difference: > > 1. Default > > > ... > + 15.95% 6.05% [kernel] [k] __vmap_pages_range_noflush > + 15.91% 1.74% [kernel] [k] addr_to_vb_xa <--------------- > + 15.13% 12.05% [kernel] [k] vunmap_p4d_range > + 14.17% 13.38% [kernel] [k] __find_nth_bit <-------------- > + 10.62% 0.00% [kernel] [k] ret_from_fork_asm > + 10.62% 0.00% [kernel] [k] ret_from_fork > + 10.62% 0.00% [kernel] [k] kthread > ... > > > 2. Check if cpu_possible() and then fallback to cpumask_nth() if not > > > ... > + 6.84% 0.29% [kernel] [k] alloc_vmap_area > + 6.80% 6.70% [kernel] [k] native_queued_spin_lock_slowpath > + 4.24% 0.09% [kernel] [k] free_vmap_block > + 2.41% 2.38% [kernel] [k] addr_to_vb_xa <----------- > + 1.94% 1.91% [kernel] [k] xas_start > ... > > > It is _worth_ to check if an index is in possible mask: > > diff --git a/mm/vmalloc.c b/mm/vmalloc.c > index 45e1506d58c3..af20f78c2cbf 100644 > --- a/mm/vmalloc.c > +++ b/mm/vmalloc.c > @@ -2542,7 +2542,10 @@ static DEFINE_PER_CPU(struct vmap_block_queue, vmap_block_queue); > static struct xarray * > addr_to_vb_xa(unsigned long addr) > { > - int index = (addr / VMAP_BLOCK_SIZE) % num_possible_cpus(); > + int index = (addr / VMAP_BLOCK_SIZE) % nr_cpu_ids; > + > + if (!cpu_possible(index)) > + index = cpumask_nth(index, cpu_possible_mask); > > return &per_cpu(vmap_block_queue, index).vmap_blocks; > } > > cpumask_nth() is not cheap. My measurements are based on a synthetic > tight test and it detects a difference. In a real workloads it should > not be visible. Having gaps is not a common case plus a "slow path" > will be mitigated by the hit against possible mask. Ah, this is consistent with my understanding from the code, thanks for confirming by testing.