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Ts'o" , Jens Axboe , Ext4 Developers List , "linux-kernel@vger.kernel.org" , linux-block , Linux-MM , Andrew Morton , Johannes Weiner , Vlastimil Babka Content-Type: text/plain; charset="UTF-8" X-Bogosity: Ham, tests=bogofilter, spamicity=0.000345, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Fri, Sep 25, 2020 at 10:48 AM Roman Gushchin wrote: > > On Fri, Sep 25, 2020 at 10:35:03AM -0700, Shakeel Butt wrote: > > On Fri, Sep 25, 2020 at 10:22 AM Shakeel Butt wrote: > > > > > > On Fri, Sep 25, 2020 at 10:17 AM Linus Torvalds > > > wrote: > > > > > > > > On Fri, Sep 25, 2020 at 9:19 AM Ming Lei wrote: > > > > > > > > > > git bisect shows the first bad commit: > > > > > > > > > > [10befea91b61c4e2c2d1df06a2e978d182fcf792] mm: memcg/slab: use a single set of > > > > > kmem_caches for all allocations > > > > > > > > > > And I have double checked that the above commit is really the first bad > > > > > commit for the list corruption issue of 'list_del corruption, ffffe1c241b00408->next > > > > > is LIST_POISON1 (dead000000000100)', > > > > > > > > Thet commit doesn't revert cleanly, but I think that's purely because > > > > we'd also need to revert > > > > > > > > 849504809f86 ("mm: memcg/slab: remove unused argument by charge_slab_page()") > > > > 74d555bed5d0 ("mm: slab: rename (un)charge_slab_page() to > > > > (un)account_slab_page()") > > > > > > > > too. > > > > > > > > Can you verify that a > > > > > > > > git revert 74d555bed5d0 849504809f86 10befea91b61 > > > > > > > > on top of current -git makes things work for you again? > > > > > > > > I'm going to do an rc8 this release simply because we have another VM > > > > issue that I hope to get fixed - but there we know what the problem > > > > and the fix _is_, it just needs some care. > > > > > > > > So if Roman (or somebody else) can see what's wrong and we can fix > > > > this quickly, we don't need to go down the revert path, but .. > > > > > > > > > > I think I have a theory. The issue is happening due to the potential > > > infinite recursion: > > > > > > [ 5060.124412] ___cache_free+0x488/0x6b0 > > > *****Second recursion > > > [ 5060.128666] kfree+0xc9/0x1d0 > > > [ 5060.131947] kmem_freepages+0xa0/0xf0 > > > [ 5060.135746] slab_destroy+0x19/0x50 > > > [ 5060.139577] slabs_destroy+0x6d/0x90 > > > [ 5060.143379] ___cache_free+0x4a3/0x6b0 > > > *****First recursion > > > [ 5060.147896] kfree+0xc9/0x1d0 > > > [ 5060.151082] kmem_freepages+0xa0/0xf0 > > > [ 5060.155121] slab_destroy+0x19/0x50 > > > [ 5060.159028] slabs_destroy+0x6d/0x90 > > > [ 5060.162920] ___cache_free+0x4a3/0x6b0 > > > [ 5060.167097] kfree+0xc9/0x1d0 > > > > > > ___cache_free() is calling cache_flusharray() to flush the local cpu > > > array_cache if the cache has more elements than the limit (ac->avail > > > >= ac->limit). > > > > > > cache_flusharray() is removing batchcount number of element from local > > > cpu array_cache and pass it slabs_destroy (if the node shared cache is > > > also full). > > > > > > Note that we have not updated local cpu array_cache size yet and > > > called slabs_destroy() which can call kfree() through > > > unaccount_slab_page(). > > > > > > We are on the same CPU and this recursive kfree again check the > > > (ac->avail >= ac->limit) and call cache_flusharray() again and recurse > > > indefinitely. > > It's a coll theory! And it explains why we haven't seen it with SLUB. > > > > > I can see two possible fixes. We can either do async kfree of > > page_obj_cgroups(page) or we can update the local cpu array_cache's > > size before slabs_destroy(). > > I wonder if something like this can fix the problem? > (completely untested). > > -- > > diff --git a/mm/slab.c b/mm/slab.c > index 684ebe5b0c7a..c94b9ccfb803 100644 > --- a/mm/slab.c > +++ b/mm/slab.c > @@ -186,6 +186,7 @@ struct array_cache { > unsigned int limit; > unsigned int batchcount; > unsigned int touched; > + bool flushing; > void *entry[]; /* > * Must have this definition in here for the proper > * alignment of array_cache. Also simplifies accessing > @@ -526,6 +527,7 @@ static void init_arraycache(struct array_cache *ac, int limit, int batch) > ac->limit = limit; > ac->batchcount = batch; > ac->touched = 0; > + ac->flushing = false; > } > } > > @@ -3368,6 +3370,11 @@ static void cache_flusharray(struct kmem_cache *cachep, struct array_cache *ac) > int node = numa_mem_id(); > LIST_HEAD(list); > > + if (ac->flushing) > + return; > + > + ac->flushing = true; > + > batchcount = ac->batchcount; > > check_irq_off(); > @@ -3404,6 +3411,7 @@ static void cache_flusharray(struct kmem_cache *cachep, struct array_cache *ac) > spin_unlock(&n->list_lock); > slabs_destroy(cachep, &list); > ac->avail -= batchcount; > + ac->flushing = false; > memmove(ac->entry, &(ac->entry[batchcount]), sizeof(void *)*ac->avail); > } > I don't think you can ignore the flushing. The __free_once() in ___cache_free() assumes there is a space available. BTW do_drain() also have the same issue. Why not move slabs_destroy() after we update ac->avail and memmove()?