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Date:   Tue, 17 Aug 2021 11:34:08 +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: <20210817093408.zanfoybsbnrdnav7@linutronix.de>
References: <2666777.vCjUEy5FO1@sven-desktop>
 <7329198a-2a4e-ebc2-abf8-f7f38f00d5e1@suse.cz>
 <20210817091224.nqnrro34cyb67chj@linutronix.de>
 <3da13f0a-2720-a38c-33a7-744668013390@suse.cz>
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On 2021-08-17 11:31:56 [+0200], Vlastimil Babka wrote:
> 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.

Without the right debugging enabled

| typedef struct {
| #ifdef CONFIG_DEBUG_LOCK_ALLOC
|         struct lockdep_map      dep_map;
|         struct task_struct      *owner;
| #endif
| } local_lock_t;

the struct is just empty.

Sebastian