linux-kernel - initialization of static per-cpu variables

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Date:	Wed, 21 May 2008 20:28:02 +0200
From:	"Vegard Nossum" <vegard.nossum@...il.com>
To:	"Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>
Cc:	"Rusty Russel" <rusty@...tcorp.com.au>
Subject: initialization of static per-cpu variables

Hi,

I encountered this comment in kernel/softirq.c:

/* Some compilers disobey section attribute on statics when not
   initialized -- RR */
static DEFINE_PER_CPU(struct tasklet_head, tasklet_vec) = { NULL };
static DEFINE_PER_CPU(struct tasklet_head, tasklet_hi_vec) = { NULL };

So I assume it's the combination of static and whatever section
DFINE_PER_CPU puts the variable in which is the problem.

However, there's a LOT of these "static DEFINE_PER_CPU" without any
initializer in the rest of the code, e.g.:

$ g 'static DEFINE_PER_CPU' kernel/sched.c
static DEFINE_PER_CPU(struct sched_entity, init_sched_entity);
static DEFINE_PER_CPU(struct cfs_rq, init_cfs_rq) ____cacheline_aligned_in_smp;
static DEFINE_PER_CPU(struct sched_rt_entity, init_sched_rt_entity);
static DEFINE_PER_CPU(struct rt_rq, init_rt_rq) ____cacheline_aligned_in_smp;
static DEFINE_PER_CPU_SHARED_ALIGNED(struct rq, runqueues);
static DEFINE_PER_CPU(unsigned long long, time_offset);
static DEFINE_PER_CPU(unsigned long long, prev_cpu_time);
static DEFINE_PER_CPU(spinlock_t, aggregate_lock);
static DEFINE_PER_CPU(struct sched_domain, cpu_domains);
static DEFINE_PER_CPU(struct sched_group, sched_group_cpus);
static DEFINE_PER_CPU(struct sched_domain, core_domains);
static DEFINE_PER_CPU(struct sched_group, sched_group_core);
static DEFINE_PER_CPU(struct sched_domain, phys_domains);
static DEFINE_PER_CPU(struct sched_group, sched_group_phys);
static DEFINE_PER_CPU(struct sched_domain, node_domains);
static DEFINE_PER_CPU(struct sched_domain, allnodes_domains);
static DEFINE_PER_CPU(struct sched_group, sched_group_allnodes);

The comment seems to be ancient and I don't know who wrote it, so I'm
making a guess that it's Rusty Russel (Cced).

So which do we do, delete the comment (on the grounds that it is
invalid) or fix these other declarations (there's a lot of them)?

Vegard

-- 
"The animistic metaphor of the bug that maliciously sneaked in while
the programmer was not looking is intellectually dishonest as it
disguises that the error is the programmer's own creation."
	-- E. W. Dijkstra, EWD1036
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