From: Peter Zijlstra <peterz@infradead.org>
To: Josh Don <joshdon@google.com>
Cc: Joel Fernandes <joel@joelfernandes.org>,
"Hyser,Chris" <chris.hyser@oracle.com>,
Ingo Molnar <mingo@kernel.org>,
Vincent Guittot <vincent.guittot@linaro.org>,
Valentin Schneider <valentin.schneider@arm.com>,
Mel Gorman <mgorman@suse.de>,
linux-kernel <linux-kernel@vger.kernel.org>,
Tejun Heo <tj@kernel.org>, Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH 9/9] sched: prctl() and cgroup interaction
Date: Tue, 6 Apr 2021 17:12:53 +0200 [thread overview]
Message-ID: <YGx6dZiAZFpN7QBt@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <CABk29NvYfAAREeBV-gcoQa+LijphCUJXqeJLWjgPr_PTYumUMQ@mail.gmail.com>
On Fri, Apr 02, 2021 at 06:30:48PM -0700, Josh Don wrote:
> Hi Peter,
>
> I walked through the reference counting, and it seems good to me
> (though it did take a few passes to fully digest the invariants for
> the fat cookie stuff).
>
> > +unsigned long sched_core_alloc_cookie(unsigned int type)
> > {
> > struct sched_core_cookie *ck = kmalloc(sizeof(*ck), GFP_KERNEL);
> > if (!ck)
> > return 0;
> > - refcount_set(&ck->refcnt, 1);
> > + WARN_ON_ONCE(type > GROUP_COOKIE);
> > + sched_core_init_cookie(ck, type);
> > sched_core_get();
> >
> > - return (unsigned long)ck;
> > + return (unsigned long)ck | type;
> > }
>
> This feels like it needs to be stronger than a WARN_ON_ONCE; could
> create a corrupted address that we later try to kfree().
The fattie is also released with kfree(), not a real problem that.
> Also, for my own edification, why will the bottom two bits here always be 0?
#define ARCH_KMALLOC_MINALIGN __alignof__(unsigned long long)
> > -unsigned long sched_core_alloc_cookie(void)
> > +static inline void *cookie_ptr(unsigned long cookie)
> > +{
> > + return (void *)(cookie & ~3UL);
> > +}
> > +
> > +static inline int cookie_type(unsigned long cookie)
> > +{
> > + return cookie & 3;
> > +}
>
> s/3/FAT_COOKIE
COOKIE_MASK if anything..
> > +#define FAT_COOKIE 0x03
>
> Move to sched.h to group with TASK/GROUP_COOKIE?
Didn't want to expose FAT outside the ifdef
> > +static unsigned long __sched_core_fat_cookie(struct task_struct *p,
> > + void **spare_fat,
> > + unsigned long cookie)
> > +{
>
> This function looks good to me, but could use some more comments about
> the pre/post-condition assumptions. Ie. cookie already has a get()
> associated with it, caller is expected to kfree the spare_fat.
Fair enough. I'll go write up something. I had to fix a refcount issue
here, which should've been clue a comment it required.
There's actually a bug with the rb tree magic too, I'll go fix.
> > + raw_spin_lock_irqsave(&fat_lock, flags);
> > + n = rb_find_add(&fat->node, &fat_root, fat_cmp);
> > + raw_spin_unlock_irqrestore(&fat_lock, flags);
> > +
> > + if (n) {
> > + sched_core_put_fat(fat);
> > + fat = node_2_fat(n);
>
> This put() doesn't seem strictly necessary; caller will be
> unconditionally freeing the spare_fat. Keep anyway for completeness,
> but add a comment?
It needs to put the references we got on constructing the new fat.
next prev parent reply other threads:[~2021-04-06 15:17 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-01 13:10 [PATCH 0/9] sched: Core scheduling interfaces Peter Zijlstra
2021-04-01 13:10 ` [PATCH 1/9] sched: Allow sched_core_put() from atomic context Peter Zijlstra
2021-04-01 13:10 ` [PATCH 2/9] sched: Implement core-sched assertions Peter Zijlstra
2021-04-01 13:10 ` [PATCH 3/9] sched: Trivial core scheduling cookie management Peter Zijlstra
2021-04-01 20:04 ` Josh Don
2021-04-02 7:13 ` Peter Zijlstra
2021-04-01 13:10 ` [PATCH 4/9] sched: Default core-sched policy Peter Zijlstra
2021-04-21 13:33 ` Peter Zijlstra
2021-04-21 14:31 ` Chris Hyser
2021-04-01 13:10 ` [PATCH 5/9] sched: prctl() core-scheduling interface Peter Zijlstra
2021-04-07 17:00 ` Peter Zijlstra
2021-04-18 3:52 ` Joel Fernandes
2021-04-01 13:10 ` [PATCH 6/9] kselftest: Add test for core sched prctl interface Peter Zijlstra
2021-04-01 13:10 ` [PATCH 7/9] sched: Cgroup core-scheduling interface Peter Zijlstra
2021-04-02 0:34 ` Josh Don
2021-04-01 13:10 ` [PATCH 8/9] rbtree: Remove const from the rb_find_add() comparator Peter Zijlstra
2021-04-01 13:10 ` [PATCH 9/9] sched: prctl() and cgroup interaction Peter Zijlstra
2021-04-03 1:30 ` Josh Don
2021-04-06 15:12 ` Peter Zijlstra [this message]
2021-04-04 23:39 ` [PATCH 0/9] sched: Core scheduling interfaces Tejun Heo
2021-04-05 18:46 ` Joel Fernandes
2021-04-06 14:16 ` Tejun Heo
2021-04-18 1:35 ` Joel Fernandes
2021-04-19 9:00 ` Peter Zijlstra
2021-04-21 13:35 ` Peter Zijlstra
2021-04-21 14:45 ` Chris Hyser
2021-04-06 15:32 ` Peter Zijlstra
2021-04-06 16:08 ` Tejun Heo
2021-04-07 18:39 ` Peter Zijlstra
2021-04-07 16:50 ` Michal Koutný
2021-04-07 18:34 ` Peter Zijlstra
2021-04-08 13:25 ` Michal Koutný
2021-04-08 15:02 ` Peter Zijlstra
2021-04-09 0:16 ` Josh Don
2021-04-19 11:30 ` Tejun Heo
2021-04-20 1:17 ` Josh Don
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