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From: Michal Hocko <mhocko@kernel.org>
To: Qian Cai <cai@lca.pw>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>,
	linux-mm@kvack.org, Andrew Morton <akpm@linux-foundation.org>,
	Vlastimil Babka <vbabka@suse.cz>,
	Oscar Salvador <osalvador@suse.de>,
	Mel Gorman <mgorman@techsingularity.net>,
	Mike Rapoport <rppt@linux.ibm.com>,
	Dan Williams <dan.j.williams@intel.com>,
	Pavel Tatashin <pavel.tatashin@microsoft.com>,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mm/page_alloc: Add a reason for reserved pages in has_unmovable_pages()
Date: Fri, 4 Oct 2019 15:38:14 +0200
Message-ID: <20191004133814.GM9578@dhcp22.suse.cz> (raw)
In-Reply-To: <1570195839.5576.273.camel@lca.pw>

On Fri 04-10-19 09:30:39, Qian Cai wrote:
> On Fri, 2019-10-04 at 15:07 +0200, Michal Hocko wrote:
> > On Fri 04-10-19 08:56:16, Qian Cai wrote:
> > [...]
> > > It might be a good time to rethink if it is really a good idea to dump_page()
> > > at all inside has_unmovable_pages(). As it is right now, it is a a potential
> > > deadlock between console vs memory offline. More details are in this thread,
> > > 
> > > https://lore.kernel.org/lkml/1568817579.5576.172.camel@lca.pw/
> > 
> > Huh. That would imply we cannot do any printk from that path, no?
> 
> Yes, or use something like printk_deferred()

This is just insane. The hotplug code is in no way special wrt printk.
It is never called from the printk code AFAIK and thus there is no real
reason why this particular code should be any special. Not to mention
it calls printk indirectly from a code that is shared with other code
paths.

> or it needs to rework of the current console locking which I have no
> clue yet.

Yes, if the lockdep is really referring to a real deadlock which I
haven't really explored.

-- 
Michal Hocko
SUSE Labs


  reply index

Thread overview: 29+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-03  8:10 Anshuman Khandual
2019-10-03  9:05 ` Qian Cai
2019-10-03  9:32   ` Anshuman Khandual
2019-10-03  9:53     ` Anshuman Khandual
2019-10-03 11:19     ` Qian Cai
2019-10-03 11:32       ` Anshuman Khandual
2019-10-03 11:50         ` Qian Cai
2019-10-03 12:02           ` Anshuman Khandual
2019-10-03 12:14             ` Qian Cai
2019-10-04  8:25               ` David Hildenbrand
2020-01-14  8:19                 ` Anshuman Khandual
2020-01-14  8:30                   ` David Hildenbrand
2020-01-14  9:10                   ` Michal Hocko
2020-01-14 10:23                     ` Vlastimil Babka
2020-01-14 11:03                       ` Anshuman Khandual
2020-01-14 11:32                       ` Michal Hocko
2020-01-14 12:04                         ` [PATCH] mm, debug: always print flags in dump_page() Vlastimil Babka
2020-01-14 13:35                           ` Michal Hocko
2020-01-14 18:22                         ` [PATCH] mm/page_alloc: Add a reason for reserved pages in has_unmovable_pages() Ralph Campbell
2019-10-04 10:58 ` Michal Hocko
2019-10-04 11:44   ` Anshuman Khandual
2019-10-04 12:56     ` Qian Cai
2019-10-04 13:07       ` Michal Hocko
2019-10-04 13:30         ` Qian Cai
2019-10-04 13:38           ` Michal Hocko [this message]
2019-10-04 13:56             ` Qian Cai
2019-10-04 14:41               ` Michal Hocko
2019-10-05 21:22                 ` Andrew Morton
2019-10-05 22:38                   ` Qian Cai

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