From: David Hildenbrand <david@redhat.com>
To: Michal Hocko <mhocko@kernel.org>, Qian Cai <cai@lca.pw>
Cc: Petr Mladek <pmladek@suse.com>,
Christian Borntraeger <borntraeger@de.ibm.com>,
Heiko Carstens <heiko.carstens@de.ibm.com>,
sergey.senozhatsky.work@gmail.com, rostedt@goodmis.org,
peterz@infradead.org, linux-mm@kvack.org,
john.ogness@linutronix.de, akpm@linux-foundation.org,
Vasily Gorbik <gor@linux.ibm.com>,
Peter Oberparleiter <oberpar@linux.ibm.com>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] mm/page_isolation: fix a deadlock with printk()
Date: Thu, 10 Oct 2019 20:59:35 +0200 [thread overview]
Message-ID: <31b7049d-ba43-10a0-8434-18c9769ac0a5@redhat.com> (raw)
In-Reply-To: <20191010180626.GL18412@dhcp22.suse.cz>
On 10.10.19 20:06, Michal Hocko wrote:
> On Thu 10-10-19 13:48:06, Qian Cai wrote:
>> On Thu, 2019-10-10 at 19:30 +0200, Michal Hocko wrote:
>>> On Thu 10-10-19 10:47:38, Qian Cai wrote:
>>>> On Thu, 2019-10-10 at 16:18 +0200, Michal Hocko wrote:
>>>>> On Thu 10-10-19 09:11:52, Qian Cai wrote:
>>>>>> On Thu, 2019-10-10 at 12:59 +0200, Michal Hocko wrote:
>>>>>>> On Thu 10-10-19 05:01:44, Qian Cai wrote:
>>>>>>>>
>>>>>>>>
>>>>>>>>> On Oct 9, 2019, at 12:23 PM, Michal Hocko <mhocko@kernel.org> wrote:
>>>>>>>>>
>>>>>>>>> If this was only about the memory offline code then I would agree. But
>>>>>>>>> we are talking about any printk from the zone->lock context and that is
>>>>>>>>> a bigger deal. Besides that it is quite natural that the printk code
>>>>>>>>> should be more universal and allow to be also called from the MM
>>>>>>>>> contexts as much as possible. If there is any really strong reason this
>>>>>>>>> is not possible then it should be documented at least.
>>>>>>>>
>>>>>>>> Where is the best place to document this? I am thinking about under
>>>>>>>> the “struct zone” definition’s lock field in mmzone.h.
>>>>>>>
>>>>>>> I am not sure TBH and I do not think we have reached the state where
>>>>>>> this would be the only way forward.
>>>>>>
>>>>>> How about I revised the changelog to focus on memory offline rather than making
>>>>>> a rule that nobody should call printk() with zone->lock held?
>>>>>
>>>>> If you are to remove the CONFIG_DEBUG_VM printk then I am all for it. I
>>>>> am still not convinced that fiddling with dump_page in the isolation
>>>>> code is justified though.
>>>>
>>>> No, dump_page() there has to be fixed together for memory offline to be useful.
>>>> What's the other options it has here?
>>>
>>> I would really prefer to not repeat myself
>>> http://lkml.kernel.org/r/20191010074049.GD18412@dhcp22.suse.cz
>>
>> Care to elaborate what does that mean? I am confused on if you finally agree on
>> no printk() while held zone->lock or not. You said "If there is absolutely
>> no way around that then we might have to bite a bullet and consider some
>> of MM locks a land of no printk." which makes me think you agreed, but your
>> stance from the last reply seems you were opposite to it.
>
> I really do mean that the first step is to remove the dependency from
> the printk and remove any allocation from the console callbacks. If that
> turns out to be infeasible then we have to bite the bullet and think of
> a way to drop all printks from all locks that participate in an atomic
> allocation requests.
>
I second that and dropping the useless printk() as Michal mentioned. I
would beg to not uglify the offlining/isolation code with __nolock
variants or dropping locks somewhere down in a function. If everything
fails, I rather want to see the prinkt's gone or returning details in a
struct back to the caller, that can print it instead.
e.g.,
struct unmovable_page_info {
const char *reason;
struct page *page;
...
};
You should get the idea.
--
Thanks,
David / dhildenb
next prev parent reply other threads:[~2019-10-10 18:59 UTC|newest]
Thread overview: 73+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-04 22:26 [PATCH v2] mm/page_isolation: fix a deadlock with printk() Qian Cai
2019-10-07 8:07 ` Michal Hocko
2019-10-07 9:05 ` Petr Mladek
2019-10-07 11:33 ` Michal Hocko
2019-10-07 12:34 ` Qian Cai
[not found] ` <FB72D947-A0F9-43E7-80D9-D7ACE33849C7@lca.pw>
2019-10-07 11:37 ` Michal Hocko
2019-10-07 12:11 ` Qian Cai
2019-10-07 12:43 ` Michal Hocko
2019-10-07 13:07 ` Qian Cai
2019-10-07 14:10 ` Petr Mladek
2019-10-07 14:30 ` Petr Mladek
2019-10-07 14:49 ` Michal Hocko
2019-10-08 7:43 ` Petr Mladek
2019-10-08 8:27 ` Michal Hocko
2019-10-08 12:56 ` Christian Borntraeger
2019-10-08 16:08 ` Qian Cai
2019-10-08 18:35 ` Michal Hocko
2019-10-08 19:06 ` Qian Cai
2019-10-08 19:17 ` Michal Hocko
2019-10-08 19:35 ` Qian Cai
2019-10-09 11:49 ` Petr Mladek
2019-10-09 13:06 ` Qian Cai
2019-10-09 13:27 ` Michal Hocko
2019-10-09 13:43 ` Qian Cai
2019-10-09 13:51 ` Michal Hocko
2019-10-09 14:19 ` Qian Cai
2019-10-09 14:34 ` Michal Hocko
2019-10-09 15:08 ` Qian Cai
2019-10-09 16:23 ` Michal Hocko
2019-10-10 9:01 ` Qian Cai
2019-10-10 10:59 ` Michal Hocko
2019-10-10 13:11 ` Qian Cai
2019-10-10 14:18 ` Michal Hocko
2019-10-10 14:47 ` Qian Cai
2019-10-10 17:30 ` Michal Hocko
2019-10-10 17:48 ` Qian Cai
2019-10-10 18:06 ` Michal Hocko
2019-10-10 18:59 ` David Hildenbrand [this message]
2019-10-09 14:24 ` Petr Mladek
2019-10-09 14:46 ` Qian Cai
2019-10-10 7:57 ` Petr Mladek
2019-10-09 11:39 ` Petr Mladek
2019-10-09 13:56 ` Peter Oberparleiter
2019-10-09 14:26 ` Michal Hocko
2019-10-10 5:12 ` Sergey Senozhatsky
2019-10-10 7:40 ` Michal Hocko
2019-10-10 8:16 ` Sergey Senozhatsky
2019-10-10 8:37 ` Michal Hocko
2019-10-10 8:21 ` Petr Mladek
2019-10-10 8:39 ` Sergey Senozhatsky
2019-10-10 11:11 ` Petr Mladek
2019-10-09 15:25 ` Qian Cai
2019-10-07 14:59 ` Qian Cai
2019-10-07 15:12 ` Michal Hocko
2019-10-07 15:33 ` Qian Cai
2019-10-08 8:15 ` Petr Mladek
2019-10-08 9:32 ` Qian Cai
2019-10-08 13:13 ` Steven Rostedt
2019-10-08 13:23 ` Qian Cai
2019-10-08 13:33 ` Steven Rostedt
2019-10-08 13:42 ` Petr Mladek
2019-10-08 13:48 ` Michal Hocko
2019-10-08 14:03 ` Qian Cai
2019-10-08 14:08 ` Michal Hocko
2019-10-08 8:40 ` Michal Hocko
2019-10-08 10:04 ` Qian Cai
2019-10-08 10:39 ` Michal Hocko
2019-10-08 12:00 ` Qian Cai
2019-10-08 12:39 ` Michal Hocko
2019-10-08 13:06 ` Qian Cai
2019-10-08 13:37 ` Michal Hocko
2019-10-08 13:08 ` Petr Mladek
2019-10-08 13:33 ` Qian Cai
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