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Date:   Tue, 17 Aug 2021 11:12:24 +0200
From:   Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To:     Vlastimil Babka <vbabka@suse.cz>
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>
Subject: Re: [PATCH v4 35/35] mm, slub: convert kmem_cpu_slab protection to
 local_lock
Message-ID: <20210817091224.nqnrro34cyb67chj@linutronix.de>
References: <2666777.vCjUEy5FO1@sven-desktop>
 <7329198a-2a4e-ebc2-abf8-f7f38f00d5e1@suse.cz>
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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. On RT it was working ;)

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