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Date: Tue, 10 Aug 2021 13:47:42 +0200 From: Mike Galbraith <efault@....de> To: Vlastimil Babka <vbabka@...e.cz>, Qian Cai <quic_qiancai@...cinc.com>, Andrew Morton <akpm@...ux-foundation.org>, Christoph Lameter <cl@...ux.com>, David Rientjes <rientjes@...gle.com>, Pekka Enberg <penberg@...nel.org>, Joonsoo Kim <iamjoonsoo.kim@....com> Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org, Sebastian Andrzej Siewior <bigeasy@...utronix.de>, Thomas Gleixner <tglx@...utronix.de>, Mel Gorman <mgorman@...hsingularity.net>, Jesper Dangaard Brouer <brouer@...hat.com>, Jann Horn <jannh@...gle.com> Subject: Re: [PATCH v4 29/35] mm: slub: Move flush_cpu_slab() invocations __free_slab() invocations out of IRQ context On Tue, 2021-08-10 at 11:03 +0200, Vlastimil Babka wrote: > On 8/9/21 3:41 PM, Qian Cai wrote: > > > > > > +static DEFINE_MUTEX(flush_lock); > > > +static DEFINE_PER_CPU(struct slub_flush_work, slub_flush); > > > + > > > static void flush_all(struct kmem_cache *s) > > > { > > > - on_each_cpu_cond(has_cpu_slab, flush_cpu_slab, s, 1); > > > + struct slub_flush_work *sfw; > > > + unsigned int cpu; > > > + > > > + mutex_lock(&flush_lock); > > > > Vlastimil, taking the lock here could trigger a warning during memory offline/online due to the locking order: > > > > slab_mutex -> flush_lock > > > > [ 91.374541] WARNING: possible circular locking dependency detected > > [ 91.381411] 5.14.0-rc5-next-20210809+ #84 Not tainted > > [ 91.387149] ------------------------------------------------------ > > [ 91.394016] lsbug/1523 is trying to acquire lock: > > [ 91.399406] ffff800018e76530 (flush_lock){+.+.}-{3:3}, at: flush_all+0x50/0x1c8 > > [ 91.407425] > > but task is already holding lock: > > [ 91.414638] ffff800018e48468 (slab_mutex){+.+.}-{3:3}, at: slab_memory_callback+0x44/0x280 > > [ 91.423603] > > which lock already depends on the new lock. > > > > OK, managed to reproduce in qemu and this fixes it for me on top of > next-20210809. Could you test as well, as your testing might be more > comprehensive? I will format is as a fixup for the proper patch in the series then. As it appeared it should, moving cpu_hotplug_lock outside slab_mutex in kmem_cache_destroy() on top of that silenced the cpu offline gripe. --- mm/slab_common.c | 2 ++ mm/slub.c | 2 +- 2 files changed, 3 insertions(+), 1 deletion(-) --- a/mm/slab_common.c +++ b/mm/slab_common.c @@ -502,6 +502,7 @@ void kmem_cache_destroy(struct kmem_cach if (unlikely(!s)) return; + cpus_read_lock(); mutex_lock(&slab_mutex); s->refcount--; @@ -516,6 +517,7 @@ void kmem_cache_destroy(struct kmem_cach } out_unlock: mutex_unlock(&slab_mutex); + cpus_read_unlock(); } EXPORT_SYMBOL(kmem_cache_destroy); --- a/mm/slub.c +++ b/mm/slub.c @@ -4234,7 +4234,7 @@ int __kmem_cache_shutdown(struct kmem_ca int node; struct kmem_cache_node *n; - flush_all(s); + flush_all_cpus_locked(s); /* Attempt to free all objects */ for_each_kmem_cache_node(s, node, n) { free_partial(s, n);
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