linux-kernel - Re: [PATCH v3 31/35] mm, slub: optionally save/restore irqs in slab

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Message-ID: <20210729154302.GF3809@techsingularity.net>
Date:   Thu, 29 Jul 2021 16:43:02 +0100
From:   Mel Gorman <mgorman@...hsingularity.net>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Christoph Lameter <cl@...ux.com>,
        David Rientjes <rientjes@...gle.com>,
        Pekka Enberg <penberg@...nel.org>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Mike Galbraith <efault@....de>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Jann Horn <jannh@...gle.com>
Subject: Re: [PATCH v3 31/35] mm, slub: optionally save/restore irqs in
 slab_[un]lock()/

On Thu, Jul 29, 2021 at 03:21:28PM +0200, Vlastimil Babka wrote:
> For PREEMPT_RT we will need to disable irqs for this bit spinlock. As a
> preparation, add a flags parameter, and an internal version that takes
> additional bool parameter to control irq saving/restoring (the flags
> parameter is compile-time unused if the bool is a constant false).
> 
> Convert ___cmpxchg_double_slab(), which also comes with the same bool
> parameter, to use the internal version.
> 
> Signed-off-by: Vlastimil Babka <vbabka@...e.cz>

On arm64 allmodconfig, the following build warning was new

 In file included from ./include/linux/spinlock.h:54,
                  from ./include/linux/mmzone.h:8,
                  from ./include/linux/gfp.h:6,
                  from ./include/linux/mm.h:10,
                  from mm/slub.c:13:
 mm/slub.c: In function '___cmpxchg_double_slab.isra.0':
 ./include/linux/irqflags.h:177:3: warning: 'flags' may be used uninitialized in this function [-Wmaybe-uninitialized]
   177 |   arch_local_irq_restore(flags);  \
       |   ^~~~~~~~~~~~~~~~~~~~~~
 mm/slub.c:408:17: note: 'flags' was declared here
   408 |   unsigned long flags;
       |                 ^~~~~
 In file included from ./include/linux/string.h:262,
                  from ./include/linux/bitmap.h:10,
                  from ./include/linux/cpumask.h:12,

No idea what's special about arm allmodconfig that confuses the
compiler.

-- 
Mel Gorman
SUSE Labs