> -----Original Message-----
> From: Henrique de Moraes Holschuh [mailto:h...@hmh.eng.br]
> Sent: Friday, September 26, 2014 12:51 AM
> To: Chao Yu
> Cc: ne...@suse.de; linux-r...@vger.kernel.org; linux-kernel@vger.kernel.org
> Subject: Re: [PATCH] md: avoid potential long delay under pers_lock
>
> On Thu, 25 Sep 2014, Chao Yu wrote:
> > printk may cause long time lapse if value of printk_delay in sysctl is
> > configured large by user. If register_md_personality takes long time to
> > print in
> > spinlock pers_lock, we may encounter high CPU usage rate when there are
> > other
> > pers_lock competitors who may be blocked to spin.
> > We can avoid this condition by moving printk out of coverage of pers_lock
> > spinlock.
> >
> > Signed-off-by: Chao Yu <chao2...@samsung.com>
> > ---
> > drivers/md/md.c | 3 ++-
> > 1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/md/md.c b/drivers/md/md.c
> > index e02de05..5fcf215 100644
> > --- a/drivers/md/md.c
> > +++ b/drivers/md/md.c
> > @@ -7200,9 +7200,10 @@ static const struct file_operations md_seq_fops = {
> >
> > int register_md_personality(struct md_personality *p)
> > {
> > + printk(KERN_INFO "md: %s personality registered for level %d\n",
> > + p->name, p->level);
> > spin_lock(&pers_lock);
> > list_add_tail(&p->list, &pers_list);
> > - printk(KERN_INFO "md: %s personality registered for level %d\n",
> > p->name, p->level);
> > spin_unlock(&pers_lock);
> > return 0;
> > }
>
> Wouldn't it make more sense to move the printk after the spin_unlock ?
As original printk msg in {,un}register_md_personality shows '{,un}registered'
which means the main job is done before printk, it's better to move the printk
after spin_unlock in both {,un}register_md_personality. But IMHO, it's another
minor issue, should we fix in this patch?
Thanks,
Yu
>
> --
> "One disk to rule them all, One disk to find them. One disk to bring
> them all and in the darkness grind them. In the Land of Redmond
> where the shadows lie." -- The Silicon Valley Tarot
> Henrique Holschuh
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