Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Subject: Re: [PATCH v4 35/35] mm, slub: convert kmem_cpu_slab protection to
 local_lock
To:     Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc:     Sven Eckelmann <sven@narfation.org>, akpm@linux-foundation.org,
        brouer@redhat.com, cl@linux.com, efault@gmx.de,
        iamjoonsoo.kim@lge.com, jannh@google.com,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        mgorman@techsingularity.net, penberg@kernel.org,
        rientjes@google.com, tglx@linutronix.de,
        Stephen Rothwell <sfr@canb.auug.org.au>,
        Peter Zijlstra <peterz@infradead.org>
References: <2666777.vCjUEy5FO1@sven-desktop>
 <7329198a-2a4e-ebc2-abf8-f7f38f00d5e1@suse.cz>
 <20210817091224.nqnrro34cyb67chj@linutronix.de>
From:   Vlastimil Babka <vbabka@suse.cz>
Message-ID: <3da13f0a-2720-a38c-33a7-744668013390@suse.cz>
Date:   Tue, 17 Aug 2021 11:31:56 +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: <20210817091224.nqnrro34cyb67chj@linutronix.de>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Precedence: bulk

On 8/17/21 11:12 AM, Sebastian Andrzej Siewior wrote:
> On 2021-08-17 10:37:48 [+0200], Vlastimil Babka wrote:
>> OK reproduced. Thanks, will investigate.
> 
> With the local_lock at the top, the needed alignment gets broken for dbl
> cmpxchg.

Right. I wondered why the checks in __pcpu_double_call_return_bool
didn't trigger. They are VM_BUG_ON() so they did trigger after enabling
DEBUG_VM.

> 
> diff --git a/include/linux/slub_def.h b/include/linux/slub_def.h
> index b5bcac29b979c..cd14aa1f9bc3c 100644
> --- a/include/linux/slub_def.h
> +++ b/include/linux/slub_def.h
> @@ -42,9 +42,9 @@ enum stat_item {
>  	NR_SLUB_STAT_ITEMS };
>  
>  struct kmem_cache_cpu {
> -	local_lock_t lock;	/* Protects the fields below except stat */
>  	void **freelist;	/* Pointer to next available object */
>  	unsigned long tid;	/* Globally unique transaction id */
> +	local_lock_t lock;	/* Protects the fields below except stat */
>  	struct page *page;	/* The slab from which we are allocating */
>  #ifdef CONFIG_SLUB_CPU_PARTIAL
>  	struct page *partial;	/* Partially allocated frozen slabs */
> 
> Sebastian
>