From: Michal Hocko <mhocko@suse.com>
To: Suren Baghdasaryan <surenb@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
David Rientjes <rientjes@google.com>,
Matthew Wilcox <willy@infradead.org>,
Johannes Weiner <hannes@cmpxchg.org>,
Roman Gushchin <guro@fb.com>, Rik van Riel <riel@surriel.com>,
Minchan Kim <minchan@kernel.org>,
Christian Brauner <christian@brauner.io>,
Christoph Hellwig <hch@infradead.org>,
Oleg Nesterov <oleg@redhat.com>,
David Hildenbrand <david@redhat.com>,
Jann Horn <jannh@google.com>, Shakeel Butt <shakeelb@google.com>,
Andy Lutomirski <luto@kernel.org>,
Christian Brauner <christian.brauner@ubuntu.com>,
Florian Weimer <fweimer@redhat.com>,
Jan Engelhardt <jengelh@inai.de>,
Linux API <linux-api@vger.kernel.org>,
linux-mm <linux-mm@kvack.org>,
LKML <linux-kernel@vger.kernel.org>,
kernel-team <kernel-team@android.com>,
"Kirill A. Shutemov" <kirill@shutemov.name>,
Andrea Arcangeli <aarcange@redhat.com>
Subject: Re: [PATCH 1/1] mm: prevent a race between process_mrelease and exit_mmap
Date: Tue, 9 Nov 2021 20:26:51 +0100 [thread overview]
Message-ID: <YYrLe2u2zbmu4LfL@dhcp22.suse.cz> (raw)
In-Reply-To: <CAJuCfpFOOgs9uZSW2Tp6uBW23rLHFeSA8o5WYQ_D_ykUcKL64Q@mail.gmail.com>
On Tue 09-11-21 11:01:02, Suren Baghdasaryan wrote:
[...]
> Discussing how the patch I want to post works for maple trees that
> Matthew is working on, I've got a question:
>
> IIUC, according to Michal's post here:
> https://lore.kernel.org/all/20170725154514.GN26723@dhcp22.suse.cz,
> unmap_vmas() can race with other mmap_lock read holders (including
> oom_reap_task_mm()) with no issues.
> Maple tree patchset requires rcu read lock or the mmap semaphore be
> held (read or write side) when walking the tree, including inside
> unmap_vmas(). When asked, he told me that he is not sure why it's
> currently "safe" to walk the vma->vm_next list in unmap_vmas() while
> another thread is reaping the mm.
> Michal (or maybe someone else), could you please clarify why
> unmap_vmas() can safely race with oom_reap_task_mm()? Or maybe my
> understanding was wrong?
I cannot really comment on the mapple tree part. But the existing
synchronization between oom reaper and exit_mmap is based on
- oom_reaper takes mmap_sem for reading
- exit_mmap sets MMF_OOM_SKIP and takes the exclusive mmap_sem before
unmap_vmas.
The oom_reaper therefore can either unmap the address space if the lock
is taken before exit_mmap or it would it would bale out on MMF_OOM_SKIP
if it takes the lock afterwards. So the reaper cannot race with
unmap_vmas.
--
Michal Hocko
SUSE Labs
next prev parent reply other threads:[~2021-11-09 19:26 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
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 [this message]
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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