From: Michal Hocko <mhocko@suse.com>
To: Matthew Wilcox <willy@infradead.org>
Cc: Suren Baghdasaryan <surenb@google.com>,
akpm@linux-foundation.org, rientjes@google.com,
hannes@cmpxchg.org, guro@fb.com, riel@surriel.com,
minchan@kernel.org, kirill@shutemov.name, aarcange@redhat.com,
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, timmurray@google.com,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
kernel-team@android.com
Subject: Re: [PATCH v3 1/2] mm: protect free_pgtables with mmap_lock write lock in exit_mmap
Date: Wed, 8 Dec 2021 16:51:58 +0100 [thread overview]
Message-ID: <YbDUnkmQP3nxd5bv@dhcp22.suse.cz> (raw)
In-Reply-To: <YbDIxA92ln+RTbUK@casper.infradead.org>
On Wed 08-12-21 15:01:24, Matthew Wilcox wrote:
> On Tue, Dec 07, 2021 at 03:08:19PM -0800, Suren Baghdasaryan wrote:
> > > > /**
> > > > * @close: Called when the VMA is being removed from the MM.
> > > > * Context: Caller holds mmap_lock.
> >
> > BTW, is the caller always required to hold mmap_lock for write or it
> > *might* hold it?
>
> __do_munmap() might hold it for read, thanks to:
>
> if (downgrade)
> mmap_write_downgrade(mm);
>
> Should probably say:
>
> * Context: User context. May sleep. Caller holds mmap_lock.
>
> I don't think we should burden the implementor of the vm_ops with the
> knowledge that the VM chooses to not hold the mmap_lock under certain
> circumstances when it doesn't matter whether it's holding the mmap_lock
> or not.
If we document it like that some code might depend on that lock to be
held. I think we only want to document that the holder itself is not
allowed to take mmap sem or a depending lock.
--
Michal Hocko
SUSE Labs
next prev parent reply other threads:[~2021-12-08 15:52 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-12-07 21:50 [PATCH v3 1/2] mm: protect free_pgtables with mmap_lock write lock in exit_mmap Suren Baghdasaryan
2021-12-07 21:50 ` [PATCH v3 2/2] mm/oom_kill: allow process_mrelease to run under mmap_lock protection Suren Baghdasaryan
2021-12-07 22:07 ` [PATCH v3 1/2] mm: protect free_pgtables with mmap_lock write lock in exit_mmap Matthew Wilcox
2021-12-07 22:47 ` Suren Baghdasaryan
2021-12-07 23:08 ` Suren Baghdasaryan
2021-12-08 8:56 ` Michal Hocko
2021-12-08 15:01 ` Matthew Wilcox
2021-12-08 15:51 ` Michal Hocko [this message]
2021-12-08 16:05 ` Matthew Wilcox
2021-12-08 16:50 ` Suren Baghdasaryan
2021-12-08 19:13 ` Suren Baghdasaryan
2021-12-08 19:22 ` Matthew Wilcox
2021-12-08 21:24 ` Suren Baghdasaryan
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