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[185.121.47.193]) by smtp.gmail.com with ESMTPSA id 4fb4d7f45d1cf-57d30563440sm5853522a12.84.2024.06.25.05.40.21 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 25 Jun 2024 05:40:22 -0700 (PDT) From: Uladzislau Rezki X-Google-Original-From: Uladzislau Rezki Date: Tue, 25 Jun 2024 14:40:20 +0200 To: Baoquan He Cc: Uladzislau Rezki , 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: <75e17b57-1178-4288-b792-4ae68b19915e@draconx.ca> <00d74f24-c49c-460e-871c-d5af64701306@draconx.ca> <20240621033005.6mccm7waduelb4m5@oppo.com> Precedence: bulk X-Mailing-List: regressions@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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. */ 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