From: Vlastimil Babka <vbabka@suse.cz>
To: Mike Galbraith <efault@gmx.de>,
Thomas Gleixner <tglx@linutronix.de>,
LKML <linux-kernel@vger.kernel.org>
Cc: linux-rt-users@vger.kernel.org,
Mel Gorman <mgorman@techsingularity.net>,
Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Subject: Re: [rfc/patch] mm/slub: restore/expand unfreeze_partials() local exclusion scope
Date: Sat, 24 Jul 2021 00:39:20 +0200 [thread overview]
Message-ID: <5be1a703-9a0a-4115-1d69-634e5e8ecefd@suse.cz> (raw)
In-Reply-To: <84a7bd02cf109c6a5a8c7cc2bfc2898cb98270aa.camel@gmx.de>
On 7/21/21 11:33 AM, Mike Galbraith wrote:
> On Wed, 2021-07-21 at 10:44 +0200, Vlastimil Babka wrote:
>>
>> So this doesn't look like our put_cpu_partial() preempted a
>> __slab_alloc() on the same cpu, right?
>
> No, likely it was the one preempted by someone long gone, but we'll
> never know without setting a trap.
>
>> BTW did my ugly patch work?
>
> Nope. I guess you missed my reporting it to have been a -ENOBOOT, and
Indeed, I misunderstood it as you talking about your patch.
> that cutting it in half, ie snagging only __slab_free() does boot, and
> seems to cure all of the RT fireworks.
OK, so depending on drain=1 makes this apply only to put_cpu_partial()
called from __slab_free and not get_partial_node(). One notable
difference is that in __slab_free we don't have n->list_lock locked and
in get_partial_node() we do. I guess in case your list_lock is made raw
again by another patch, that explains a local_lock can't nest under it.
If not, then I would expect this to work (I don't think they ever nest
in the opposite order, also lockdep should tell us instead of
-ENOBOOT?), but might be missing something...
I'd rather not nest those locks in any case. I just need to convince
myself that the scenario the half-fix fixes is indeed the only one
that's needed and we're not leaving there other races that are just
harder to trigger...
> (chainsaw noises...)
>
> ---
> mm/slub.c | 12 +++++++++++-
> 1 file changed, 11 insertions(+), 1 deletion(-)
>
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -2551,6 +2551,8 @@ static void put_cpu_partial(struct kmem_
> int pobjects;
>
> slub_get_cpu_ptr(s->cpu_slab);
> + if (IS_ENABLED(CONFIG_PREEMPT_RT) && drain)
> + local_lock(&s->cpu_slab->lock);
> do {
> pages = 0;
> pobjects = 0;
> @@ -2564,7 +2566,13 @@ static void put_cpu_partial(struct kmem_
> * partial array is full. Move the existing
> * set to the per node partial list.
> */
> - unfreeze_partials(s);
> + this_cpu_write(s->cpu_slab->partial, NULL);
> + if (IS_ENABLED(CONFIG_PREEMPT_RT) && drain)
> + local_unlock(&s->cpu_slab->lock);
> + __unfreeze_partials(s, oldpage);
> + if (IS_ENABLED(CONFIG_PREEMPT_RT) && drain)
> + local_lock(&s->cpu_slab->lock);
> +
> oldpage = NULL;
> pobjects = 0;
> pages = 0;
> @@ -2581,6 +2589,8 @@ static void put_cpu_partial(struct kmem_
>
> } while (this_cpu_cmpxchg(s->cpu_slab->partial, oldpage, page)
> != oldpage);
> + if (IS_ENABLED(CONFIG_PREEMPT_RT) && drain)
> + local_unlock(&s->cpu_slab->lock);
> slub_put_cpu_ptr(s->cpu_slab);
> #endif /* CONFIG_SLUB_CPU_PARTIAL */
> }
>
>
next prev parent reply other threads:[~2021-07-23 22:39 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-08 9:42 [ANNOUNCE] v5.13-rt1 Thomas Gleixner
2021-07-09 5:20 ` [patch] mm/slub: Fix kmem_cache_alloc_bulk() error path Mike Galbraith
2021-07-09 5:20 ` [patch] mm/slub: Replace do_slab_free() local_lock_irqsave/restore() calls in PREEMPT_RT scope Mike Galbraith
2021-07-09 5:21 ` [rfc/patch] mm/slub: restore/expand unfreeze_partials() local exclusion scope Mike Galbraith
2021-07-09 5:25 ` Mike Galbraith
2021-07-09 19:28 ` Thomas Gleixner
2021-07-10 1:12 ` Mike Galbraith
2021-07-15 16:34 ` Mike Galbraith
2021-07-17 14:58 ` [patch] v2 " Mike Galbraith
2021-07-18 7:58 ` Vlastimil Babka
2021-07-18 8:11 ` Mike Galbraith
2021-07-18 15:43 ` Mike Galbraith
2021-07-18 21:19 ` Vlastimil Babka
2021-07-19 4:01 ` Mike Galbraith
2021-07-19 13:15 ` Mike Galbraith
2021-07-20 2:46 ` kernel test robot
2021-07-20 8:56 ` [rfc/patch] " Vlastimil Babka
2021-07-20 11:26 ` Mike Galbraith
2021-07-21 4:56 ` Mike Galbraith
2021-07-21 8:44 ` Vlastimil Babka
2021-07-21 9:33 ` Mike Galbraith
2021-07-23 22:39 ` Vlastimil Babka [this message]
2021-07-24 2:25 ` Mike Galbraith
2021-07-25 14:09 ` Mike Galbraith
2021-07-25 14:16 ` Vlastimil Babka
2021-07-25 15:02 ` Mike Galbraith
2021-07-25 16:27 ` Vlastimil Babka
2021-07-25 19:12 ` Vlastimil Babka
2021-07-25 19:34 ` Vlastimil Babka
2021-07-26 10:04 ` Mike Galbraith
2021-07-26 17:00 ` Mike Galbraith
2021-07-26 21:26 ` Vlastimil Babka
2021-07-27 4:09 ` Mike Galbraith
2021-07-28 16:59 ` Vlastimil Babka
2021-07-29 4:51 ` Mike Galbraith
2021-07-29 9:51 ` Vlastimil Babka
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