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Tue, 25 Jun 2024 09:02:53 -0400 X-MC-Unique: TdHssLFeNoemz-W2EyYJVQ-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-02.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 6A60F1956094; Tue, 25 Jun 2024 13:02:51 +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 095CF1956087; Tue, 25 Jun 2024 13:02:49 +0000 (UTC) Date: Tue, 25 Jun 2024 21:02:43 +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: <00d74f24-c49c-460e-871c-d5af64701306@draconx.ca> <20240621033005.6mccm7waduelb4m5@oppo.com> 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 X-Stat-Signature: dqfunsfbjopjc1t694iwdszzf8k4yhzq X-Rspamd-Queue-Id: A68F61C002A X-Rspam-User: X-Rspamd-Server: rspam10 X-HE-Tag: 1719320577-898336 X-HE-Meta: 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 cDysIGrB pJvOHcTJGsnUNKKDJMQiZ1CYvdsybwjPaI7JxrL2oC/8zNxwsxW7xW6iaBgKP9a+sfIm+R2cBZVI/7BYFUfTLDcVKjdkXpXyRpEi//dPF/SIkTdviRmh/MKOxq9kvGuuMyWom6PBghY9/RzLSpqD1vZbXIjT84kz5Ku7rfgTdhkund2dZIfCLhgT8o9uz3/slGMDw9yvDTUME5aDhpJiCnrRrb96SYCOo/x5PFWz0smP5go1EgaT7LIk51hPzWI+ClUww+AIGiqYZX0Hzxn+IEmTsCn1i/oKXmGGQ42Yl6FyhciYbO0zU/l71juscAzSYRPRHwjnOiV3Aaxk= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 06/25/24 at 02:40pm, Uladzislau Rezki wrote: > On Tue, Jun 25, 2024 at 07:40:21PM +0800, Baoquan He wrote: > > On 06/25/24 at 12:32pm, Uladzislau Rezki wrote: > > > On Tue, Jun 25, 2024 at 11:30:33AM +0800, Baoquan He wrote: > > > > On 06/24/24 at 02:16pm, Uladzislau Rezki wrote: > > > > > On Fri, Jun 21, 2024 at 10:02:50PM +0800, Baoquan He wrote: > > > > > > On 06/21/24 at 11:44am, Uladzislau Rezki wrote: > > > > > > > On Fri, Jun 21, 2024 at 03:07:16PM +0800, Baoquan He wrote: > > > > > > > > On 06/21/24 at 11:30am, Hailong Liu wrote: > > > > > > > > > On Thu, 20. Jun 14:02, Nick Bowler wrote: > > > > > > > > > > On 2024-06-20 02:19, Nick Bowler wrote: > > > > > > ...... > > > > > > > > diff --git a/mm/vmalloc.c b/mm/vmalloc.c > > > > > > > > index be2dd281ea76..18e87cafbaf2 100644 > > > > > > > > --- a/mm/vmalloc.c > > > > > > > > +++ b/mm/vmalloc.c > > > > > > > > @@ -2542,7 +2542,7 @@ 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; > > > > > > > > > > > > > > > > return &per_cpu(vmap_block_queue, index).vmap_blocks; > > > > > > > > } > > > > > > > > > > > > > > > The problem i see is about not-initializing of the: > > > > > > > > > > > > > > for_each_possible_cpu(i) { > > > > > > > struct vmap_block_queue *vbq; > > > > > > > struct vfree_deferred *p; > > > > > > > > > > > > > > vbq = &per_cpu(vmap_block_queue, i); > > > > > > > spin_lock_init(&vbq->lock); > > > > > > > INIT_LIST_HEAD(&vbq->free); > > > > > > > p = &per_cpu(vfree_deferred, i); > > > > > > > init_llist_head(&p->list); > > > > > > > INIT_WORK(&p->wq, delayed_vfree_work); > > > > > > > xa_init(&vbq->vmap_blocks); > > > > > > > } > > > > > > > > > > > > > > > > > > > > > correctly or fully. It is my bad i did not think that CPUs in a possible mask > > > > > > > can be non sequential :-/ > > > > > > > > > > > > > > nr_cpu_ids - is not the max possible CPU. For example, in Nick case, > > > > > > > when he has two CPUs, num_possible_cpus() and nr_cpu_ids are the same. > > > > > > > > > > > > I checked the generic version of setup_nr_cpu_ids(), from codes, they > > > > > > are different with my understanding. > > > > > > > > > > > > kernel/smp.c > > > > > > void __init setup_nr_cpu_ids(void) > > > > > > { > > > > > > set_nr_cpu_ids(find_last_bit(cpumask_bits(cpu_possible_mask), NR_CPUS) + 1); > > > > > > } > > > > > > > > > > > I see that it is not a weak function, so it is generic, thus the > > > > > behavior can not be overwritten, which is great. This does what we > > > > > need. > > > > > > > > > > Thank you for checking this you are right! > > > > > > > > Thanks for confirming this. > > > > > > > > > > > > > > Then it is just a matter of proper initialization of the hash: > > > > > > > > > > > > > > > diff --git a/mm/vmalloc.c b/mm/vmalloc.c > > > > > index 5d3aa2dc88a8..1733946f7a12 100644 > > > > > --- a/mm/vmalloc.c > > > > > +++ b/mm/vmalloc.c > > > > > @@ -5087,7 +5087,13 @@ void __init vmalloc_init(void) > > > > > */ > > > > > vmap_area_cachep = KMEM_CACHE(vmap_area, SLAB_PANIC); > > > > > > > > > > - for_each_possible_cpu(i) { > > > > > + /* > > > > > + * We use "nr_cpu_ids" here because some architectures > > > > > + * may have "gaps" in cpu-possible-mask. It is OK for > > > > > + * per-cpu approaches but is not OK for cases where it > > > > > + * can be used as hashes also. > > > > > + */ > > > > > + for (i = 0; i < nr_cpu_ids; i++) { > > > > > > > > I was wrong about earlier comments. Percpu variables are only available > > > > on possible CPUs. For those nonexistent possible CPUs of static percpu > > > > variable vmap_block_queue, there isn't memory allocated and mapped for > > > > them. So accessing into them will cause problem. > > > > > > > > In Nick's case, there are only CPU0, CPU2. If you access > > > > &per_cpu(vmap_block_queue, 1), problem occurs. So I think we may need to > > > > change to take other way for vbq. E.g: > > > > 1) Storing the vb in the nearest neighbouring vbq on possible CPU as > > > > below draft patch; > > > > 2) create an normal array to store vbq of size nr_cpu_ids, then we can > > > > store/fetch each vbq on non-possible CPU? > > > > > > > A correct way, i think, is to create a normal array. A quick fix can be > > > to stick to a next possible CPU. > > > > > > > The way 1) is simpler, the existing code can be adapted a little just as > > > > below. > > > > > > > > diff --git a/mm/vmalloc.c b/mm/vmalloc.c > > > > index 633363997dec..59a8951cc6c0 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(idex)) > > > > + index = cpumask_next(index, cpu_possible_mask); > > > > > > > cpumask_next() can return nr_cpu_ids if no next bits set. > > > > It won't. nr_cpu_ids is the largest index + 1, the hashed index will > > be: 0 =< index <= (nr_cpu_ids - 1) e.g cpu_possible_mask is > > b10001111, the nr_cpu_ids is 8, the largest bit is cpu7. > > cpu_possible(index) will check that. So the largest bit of cpumask_next() > > returns is (nr_cpu_ids - 1). > > > /** > * 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? > */ > static inline > unsigned int cpumask_next(int n, const struct cpumask *srcp) > { > /* -1 is a legal arg here. */ > if (n != -1) > cpumask_check(n); > return find_next_bit(cpumask_bits(srcp), small_cpumask_bits, n + 1); > } > > -- > Uladzislau Rezki >