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Date:   Mon, 4 May 2020 14:25:12 -0700 (PDT)
From:   David Rientjes <rientjes@google.com>
To:     Kevin Hao <haokexin@gmail.com>
cc:     linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        Christoph Lameter <cl@linux.com>,
        Pekka Enberg <penberg@kernel.org>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
        Thomas Gleixner <tglx@linutronix.de>,
        Steven Rostedt <rostedt@goodmis.org>
Subject: Re: [PATCH v5.6-rt] mm: slub: Always flush the delayed empty slubs
 in flush_all()
In-Reply-To: <20200504033407.2385-1-haokexin@gmail.com>
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References: <20200504033407.2385-1-haokexin@gmail.com>
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On Mon, 4 May 2020, Kevin Hao wrote:

> After commit f0b231101c94 ("mm/SLUB: delay giving back empty slubs to
> IRQ enabled regions"), when the free_slab() is invoked with the IRQ
> disabled, the empty slubs are moved to a per-CPU list and will be
> freed after IRQ enabled later. But in the current codes, there is
> a check to see if there really has the cpu slub on a specific cpu
> before flushing the delayed empty slubs, this may cause a reference
> of already released kmem_cache in a scenario like below:
> 	cpu 0				cpu 1
>   kmem_cache_destroy()
>     flush_all()
>                          --->IPI       flush_cpu_slab()
>                                          flush_slab()
>                                            deactivate_slab()
>                                              discard_slab()
>                                                free_slab()
>                                              c->page = NULL;
>       for_each_online_cpu(cpu)
>         if (!has_cpu_slab(1, s))
>           continue
>         this skip to flush the delayed
>         empty slub released by cpu1
>     kmem_cache_free(kmem_cache, s)
> 
>                                        kmalloc()
>                                          __slab_alloc()
>                                             free_delayed()
>                                             __free_slab()
>                                             reference to released kmem_cache
> 
> Fixes: f0b231101c94 ("mm/SLUB: delay giving back empty slubs to IRQ enabled regions")
> Signed-off-by: Kevin Hao <haokexin@gmail.com>

Acked-by: David Rientjes <rientjes@google.com>