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From: Andrew Morton <akpm@linux-foundation.org>
To: Suren Baghdasaryan <surenb@google.com>
Cc: mhocko@kernel.org, mhocko@suse.com, rientjes@google.com,
	willy@infradead.org, hannes@cmpxchg.org, guro@fb.com,
	riel@surriel.com, minchan@kernel.org, christian@brauner.io,
	hch@infradead.org, oleg@redhat.com, david@redhat.com,
	jannh@google.com, shakeelb@google.com, luto@kernel.org,
	christian.brauner@ubuntu.com, fweimer@redhat.com,
	jengelh@inai.de, linux-api@vger.kernel.org, linux-mm@kvack.org,
	linux-kernel@vger.kernel.org, kernel-team@android.com
Subject: Re: [PATCH 1/1] mm: prevent a race between process_mrelease and exit_mmap
Date: Thu, 21 Oct 2021 19:24:54 -0700	[thread overview]
Message-ID: <20211021192454.72ada9b3d59460cc3c037d2c@linux-foundation.org> (raw)
In-Reply-To: <20211022014658.263508-1-surenb@google.com>

On Thu, 21 Oct 2021 18:46:58 -0700 Suren Baghdasaryan <surenb@google.com> wrote:

> Race between process_mrelease and exit_mmap, where free_pgtables is
> called while __oom_reap_task_mm is in progress, leads to kernel crash
> during pte_offset_map_lock call. oom-reaper avoids this race by setting
> MMF_OOM_VICTIM flag and causing exit_mmap to take and release
> mmap_write_lock, blocking it until oom-reaper releases mmap_read_lock.
> Reusing MMF_OOM_VICTIM for process_mrelease would be the simplest way to
> fix this race, however that would be considered a hack. Fix this race
> by elevating mm->mm_users and preventing exit_mmap from executing until
> process_mrelease is finished. Patch slightly refactors the code to adapt
> for a possible mmget_not_zero failure.
> This fix has considerable negative impact on process_mrelease performance
> and will likely need later optimization.

Has the impact been quantified?

And where's the added cost happening?  The changes all look quite
lightweight?


  reply	other threads:[~2021-10-22  2:25 UTC|newest]

Thread overview: 32+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-10-22  1:46 [PATCH 1/1] mm: prevent a race between process_mrelease and exit_mmap Suren Baghdasaryan
2021-10-22  2:24 ` Andrew Morton [this message]
2021-10-22  5:23   ` Suren Baghdasaryan
2021-10-22  8:03 ` Michal Hocko
2021-10-22 11:32   ` Matthew Wilcox
2021-10-22 12:04     ` Michal Hocko
2021-10-22 17:38   ` Suren Baghdasaryan
2021-10-27 16:08     ` Suren Baghdasaryan
2021-10-27 17:33       ` Matthew Wilcox
2021-10-27 17:42         ` Suren Baghdasaryan
2021-10-27 17:51           ` Matthew Wilcox
2021-10-27 18:00             ` Suren Baghdasaryan
2021-10-29 13:03       ` Michal Hocko
2021-10-29 16:07         ` Suren Baghdasaryan
2021-11-01  8:37           ` Michal Hocko
2021-11-01 15:44             ` Suren Baghdasaryan
2021-11-01 19:59               ` Suren Baghdasaryan
2021-11-02  7:58               ` Michal Hocko
2021-11-02 15:14                 ` Suren Baghdasaryan
2021-11-09 19:01                   ` Suren Baghdasaryan
2021-11-09 19:26                     ` Michal Hocko
2021-11-09 19:37                       ` Suren Baghdasaryan
2021-11-09 19:50                         ` Michal Hocko
2021-11-09 20:02                           ` Suren Baghdasaryan
2021-11-09 20:10                             ` Michal Hocko
2021-11-09 21:10                               ` Suren Baghdasaryan
2021-11-11  1:49                                 ` Suren Baghdasaryan
2021-11-11  9:20                                   ` Michal Hocko
2021-11-11 15:02                                     ` Suren Baghdasaryan
2021-11-12  8:58                                       ` Michal Hocko
2021-11-12 16:00                                         ` Suren Baghdasaryan
2021-11-09 19:41                       ` Michal Hocko

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