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From: Peter Zijlstra <peterz@infradead.org>
To: Michal Hocko <mhocko@kernel.org>
Cc: Bart Van Assche <Bart.VanAssche@wdc.com>,
	"yang.s@alibaba-inc.com" <yang.s@alibaba-inc.com>,
	"akpm@linux-foundation.org" <akpm@linux-foundation.org>,
	"joe@perches.com" <joe@perches.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"linux-mm@kvack.org" <linux-mm@kvack.org>,
	"mingo@redhat.com" <mingo@redhat.com>
Subject: Re: [PATCH] mm: use in_atomic() in print_vma_addr()
Date: Mon, 6 Nov 2017 13:00:25 +0100	[thread overview]
Message-ID: <20171106120025.GH3165@worktop.lehotels.local> (raw)
In-Reply-To: <20171106104354.2jlgd2m4j4gxx4qo@dhcp22.suse.cz>

On Mon, Nov 06, 2017 at 11:43:54AM +0100, Michal Hocko wrote:
> > Yes the comment is very much accurate.
> 
> Which suggests that print_vma_addr might be problematic, right?
> Shouldn't we do trylock on mmap_sem instead?

Yes that's complete rubbish. trylock will get spurious failures to print
when the lock is contended.

The right solution is to not call this thing when you can't schedule,
trying to divine the state in the print function is doomed to failure.

WARNING: multiple messages have this Message-ID (diff)
From: Peter Zijlstra <peterz@infradead.org>
To: Michal Hocko <mhocko@kernel.org>
Cc: Bart Van Assche <Bart.VanAssche@wdc.com>,
	"yang.s@alibaba-inc.com" <yang.s@alibaba-inc.com>,
	"akpm@linux-foundation.org" <akpm@linux-foundation.org>,
	"joe@perches.com" <joe@perches.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"linux-mm@kvack.org" <linux-mm@kvack.org>,
	"mingo@redhat.com" <mingo@redhat.com>
Subject: Re: [PATCH] mm: use in_atomic() in print_vma_addr()
Date: Mon, 6 Nov 2017 13:00:25 +0100	[thread overview]
Message-ID: <20171106120025.GH3165@worktop.lehotels.local> (raw)
In-Reply-To: <20171106104354.2jlgd2m4j4gxx4qo@dhcp22.suse.cz>

On Mon, Nov 06, 2017 at 11:43:54AM +0100, Michal Hocko wrote:
> > Yes the comment is very much accurate.
> 
> Which suggests that print_vma_addr might be problematic, right?
> Shouldn't we do trylock on mmap_sem instead?

Yes that's complete rubbish. trylock will get spurious failures to print
when the lock is contended.

The right solution is to not call this thing when you can't schedule,
trying to divine the state in the print function is doomed to failure.

--
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  parent reply	other threads:[~2017-11-06 12:00 UTC|newest]

Thread overview: 36+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-11-01 21:38 [PATCH] mm: use in_atomic() in print_vma_addr() Yang Shi
2017-11-01 21:38 ` Yang Shi
2017-11-02  7:57 ` Michal Hocko
2017-11-02  7:57   ` Michal Hocko
2017-11-02 17:44   ` Yang Shi
2017-11-02 17:44     ` Yang Shi
2017-11-03  8:29     ` Michal Hocko
2017-11-03  8:29       ` Michal Hocko
2017-11-03 18:02     ` Andrew Morton
2017-11-03 18:02       ` Andrew Morton
2017-11-03 18:16       ` Yang Shi
2017-11-03 18:16         ` Yang Shi
2017-11-03 20:09       ` Bart Van Assche
2017-11-03 20:09         ` Bart Van Assche
2017-11-05  8:19         ` Michal Hocko
2017-11-05  8:19           ` Michal Hocko
2017-11-06 10:05           ` Peter Zijlstra
2017-11-06 10:05             ` Peter Zijlstra
2017-11-06 10:43             ` Michal Hocko
2017-11-06 10:43               ` Michal Hocko
2017-11-06 10:56               ` Michal Hocko
2017-11-06 10:56                 ` Michal Hocko
2017-11-06 12:00               ` Peter Zijlstra [this message]
2017-11-06 12:00                 ` Peter Zijlstra
2017-11-06 12:12                 ` Michal Hocko
2017-11-06 12:12                   ` Michal Hocko
2017-11-06 13:40                   ` [PATCH] mm: do not rely on preempt_count in print_vma_addr (was: Re: [PATCH] mm: use in_atomic() in print_vma_addr()) Michal Hocko
2017-11-06 13:40                     ` Michal Hocko
2017-11-06 14:19                     ` [PATCH] mm: do not rely on preempt_count in print_vma_addr Vlastimil Babka
2017-11-06 14:19                       ` Vlastimil Babka
2017-11-06 14:28                       ` Michal Hocko
2017-11-06 14:28                         ` Michal Hocko
2017-11-06 16:16                     ` Yang Shi
2017-11-06 16:16                       ` Yang Shi
2017-11-06 16:24                       ` Michal Hocko
2017-11-06 16:24                         ` Michal Hocko

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