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From: Waiman Long <llong@redhat.com>
To: Thomas Gleixner <tglx@linutronix.de>,
	Johannes Weiner <hannes@cmpxchg.org>,
	Michal Hocko <mhocko@kernel.org>,
	Vladimir Davydov <vdavydov.dev@gmail.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Vlastimil Babka <vbabka@suse.cz>, Roman Gushchin <guro@fb.com>
Cc: linux-kernel@vger.kernel.org, cgroups@vger.kernel.org,
	linux-mm@kvack.org, Shakeel Butt <shakeelb@google.com>,
	Muchun Song <songmuchun@bytedance.com>,
	Luis Goncalves <lgoncalv@redhat.com>,
	Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
	Daniel Bristot de Oliveira <bristot@redhat.com>,
	Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [PATCH] mm/memcg: Disable task obj_stock for PREEMPT_RT
Date: Wed, 4 Aug 2021 12:00:47 -0400	[thread overview]
Message-ID: <ce048e8b-bd2d-7517-d8e0-f74be98b8dee@redhat.com> (raw)
In-Reply-To: <8953e099-356e-ee09-a701-f4c7f4cda487@redhat.com>

On 8/3/21 9:40 PM, Waiman Long wrote:
> On 8/3/21 7:21 PM, Thomas Gleixner wrote:
>> To complete the analysis of drain_local_stock(). AFAICT that function
>> can only be called from task context. So what is the purpose of this
>> in_task() conditional there?
>>
>>     if (in_task())
>>            drain_obj_stock(&stock->task_obj);
> I haven't done a full analysis to see if it can be called from task 
> context only. Maybe in_task() check isn't needed, but having it there 
> provides the safety that it will still work in case it can be called 
> from interrupt context. 

After looking at possible call chains that can lead to 
drain_local_stock(), one call chain comes from the allocation of slab 
objects which I had previously determined to be callable from interrupt 
context. So it is prudent to add a in_task() check here.

Cheers,
Longman


WARNING: multiple messages have this Message-ID (diff)
From: Waiman Long <llong-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
To: Thomas Gleixner <tglx-hfZtesqFncYOwBW4kG4KsQ@public.gmane.org>,
	Johannes Weiner <hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org>,
	Michal Hocko <mhocko-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>,
	Vladimir Davydov
	<vdavydov.dev-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>,
	Andrew Morton
	<akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>,
	Vlastimil Babka <vbabka-AlSwsSmVLrQ@public.gmane.org>,
	Roman Gushchin <guro-b10kYP2dOMg@public.gmane.org>
Cc: linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org,
	Shakeel Butt <shakeelb-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>,
	Muchun Song <songmuchun-EC8Uxl6Npydl57MIdRCFDg@public.gmane.org>,
	Luis Goncalves <lgoncalv-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>,
	Sebastian Andrzej Siewior
	<bigeasy-hfZtesqFncYOwBW4kG4KsQ@public.gmane.org>,
	Daniel Bristot de Oliveira
	<bristot-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>,
	Linus Torvalds
	<torvalds-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>
Subject: Re: [PATCH] mm/memcg: Disable task obj_stock for PREEMPT_RT
Date: Wed, 4 Aug 2021 12:00:47 -0400	[thread overview]
Message-ID: <ce048e8b-bd2d-7517-d8e0-f74be98b8dee@redhat.com> (raw)
In-Reply-To: <8953e099-356e-ee09-a701-f4c7f4cda487-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>

On 8/3/21 9:40 PM, Waiman Long wrote:
> On 8/3/21 7:21 PM, Thomas Gleixner wrote:
>> To complete the analysis of drain_local_stock(). AFAICT that function
>> can only be called from task context. So what is the purpose of this
>> in_task() conditional there?
>>
>>     if (in_task())
>>            drain_obj_stock(&stock->task_obj);
> I haven't done a full analysis to see if it can be called from task 
> context only. Maybe in_task() check isn't needed, but having it there 
> provides the safety that it will still work in case it can be called 
> from interrupt context. 

After looking at possible call chains that can lead to 
drain_local_stock(), one call chain comes from the allocation of slab 
objects which I had previously determined to be callable from interrupt 
context. So it is prudent to add a in_task() check here.

Cheers,
Longman


  parent reply	other threads:[~2021-08-04 16:00 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-03 17:55 [PATCH] mm/memcg: Disable task obj_stock for PREEMPT_RT Waiman Long
2021-08-03 17:55 ` Waiman Long
2021-08-03 23:21 ` Thomas Gleixner
2021-08-03 23:21   ` Thomas Gleixner
2021-08-03 23:21   ` Thomas Gleixner
2021-08-04  1:40   ` Waiman Long
2021-08-04  1:40     ` Waiman Long
2021-08-04  8:52     ` Michal Hocko
2021-08-04  8:52       ` Michal Hocko
2021-08-04 16:00     ` Waiman Long [this message]
2021-08-04 16:00       ` Waiman Long
2021-08-04  7:39   ` Vlastimil Babka
2021-08-04  7:39     ` Vlastimil Babka
2021-08-04  8:33     ` Michal Hocko
2021-08-09  9:07       ` Michal Hocko
2021-08-09  9:07         ` Michal Hocko
2021-08-09  9:28         ` Vlastimil Babka
2021-08-09  9:28           ` Vlastimil Babka

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