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Tue, 10 Aug 2021 09:03:03 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap1.suse-dmz.suse.de with ESMTPSA id uq9+DMdAEmHSYAAAGKfGzw (envelope-from ); Tue, 10 Aug 2021 09:03:03 +0000 Subject: Re: [PATCH v4 29/35] mm: slub: Move flush_cpu_slab() invocations __free_slab() invocations out of IRQ context To: Qian Cai , Andrew Morton , Christoph Lameter , David Rientjes , Pekka Enberg , Joonsoo Kim Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Mike Galbraith , Sebastian Andrzej Siewior , Thomas Gleixner , Mel Gorman , Jesper Dangaard Brouer , Jann Horn References: <20210805152000.12817-1-vbabka@suse.cz> <20210805152000.12817-30-vbabka@suse.cz> <0b36128c-3e12-77df-85fe-a153a714569b@quicinc.com> From: Vlastimil Babka Message-ID: Date: Tue, 10 Aug 2021 11:03:02 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.12.0 MIME-Version: 1.0 In-Reply-To: <0b36128c-3e12-77df-85fe-a153a714569b@quicinc.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: D54F07006216 Authentication-Results: imf02.hostedemail.com; dkim=pass header.d=suse.cz header.s=susede2_rsa header.b=yg60EuW5; dkim=pass header.d=suse.cz header.s=susede2_ed25519 header.b=eefVtVgL; dmarc=none; spf=pass (imf02.hostedemail.com: domain of vbabka@suse.cz designates 195.135.220.29 as permitted sender) smtp.mailfrom=vbabka@suse.cz X-Stat-Signature: jqeean6x3hw6e1dt5pkwnpg3f5a4smwg X-HE-Tag: 1628586184-354094 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: 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. ----8<---- >From 7ce71c7f9455e8b96dc1b728ea566b6ef5e424e4 Mon Sep 17 00:00:00 2001 From: Vlastimil Babka Date: Tue, 10 Aug 2021 10:58:07 +0200 Subject: [PATCH] mm, slub: fix memory offline lockdep splat Reverse order of flush_lock and cpus_read_lock() to prevent lockdep splat. In slab_mem_going_offline_callback() we already have cpus_read_lock() held so make sure it's not taken again. Signed-off-by: Vlastimil Babka --- mm/slub.c | 27 ++++++++++++++++++++------- 1 file changed, 20 insertions(+), 7 deletions(-) diff --git a/mm/slub.c b/mm/slub.c index 88a6c3ed2751..073cdd4b020f 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -2640,13 +2640,13 @@ static bool has_cpu_slab(int cpu, struct kmem_cache *s) static DEFINE_MUTEX(flush_lock); static DEFINE_PER_CPU(struct slub_flush_work, slub_flush); -static void flush_all(struct kmem_cache *s) +static void flush_all_cpus_locked(struct kmem_cache *s) { struct slub_flush_work *sfw; unsigned int cpu; + lockdep_assert_cpus_held(); mutex_lock(&flush_lock); - cpus_read_lock(); for_each_online_cpu(cpu) { sfw = &per_cpu(slub_flush, cpu); @@ -2667,10 +2667,16 @@ static void flush_all(struct kmem_cache *s) flush_work(&sfw->work); } - cpus_read_unlock(); mutex_unlock(&flush_lock); } +static void flush_all(struct kmem_cache *s) +{ + cpus_read_lock(); + flush_all_cpus_locked(s); + cpus_read_unlock(); +} + /* * Use the cpu notifier to insure that the cpu slabs are flushed when * necessary. @@ -4516,7 +4522,7 @@ EXPORT_SYMBOL(kfree); * being allocated from last increasing the chance that the last objects * are freed in them. */ -int __kmem_cache_shrink(struct kmem_cache *s) +int __kmem_cache_do_shrink(struct kmem_cache *s) { int node; int i; @@ -4528,7 +4534,6 @@ int __kmem_cache_shrink(struct kmem_cache *s) unsigned long flags; int ret = 0; - flush_all(s); for_each_kmem_cache_node(s, node, n) { INIT_LIST_HEAD(&discard); for (i = 0; i < SHRINK_PROMOTE_MAX; i++) @@ -4578,13 +4583,21 @@ int __kmem_cache_shrink(struct kmem_cache *s) return ret; } +int __kmem_cache_shrink(struct kmem_cache *s) +{ + flush_all(s); + return __kmem_cache_do_shrink(s); +} + static int slab_mem_going_offline_callback(void *arg) { struct kmem_cache *s; mutex_lock(&slab_mutex); - list_for_each_entry(s, &slab_caches, list) - __kmem_cache_shrink(s); + list_for_each_entry(s, &slab_caches, list) { + flush_all_cpus_locked(s); + __kmem_cache_do_shrink(s); + } mutex_unlock(&slab_mutex); return 0; -- 2.32.0