From: Suren Baghdasaryan <surenb@google.com>
To: Oleksandr Natalenko <oleksandr@redhat.com>
Cc: Minchan Kim <minchan@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
LKML <linux-kernel@vger.kernel.org>,
linux-mm <linux-mm@kvack.org>,
linux-api@vger.kernel.org, Tim Murray <timmurray@google.com>,
Daniel Colascione <dancol@google.com>,
Sandeep Patil <sspatil@google.com>,
Sonny Rao <sonnyrao@google.com>,
Brian Geffon <bgeffon@google.com>,
Michal Hocko <mhocko@suse.com>,
Johannes Weiner <hannes@cmpxchg.org>,
Shakeel Butt <shakeelb@google.com>,
John Dias <joaodias@google.com>,
Joel Fernandes <joel@joelfernandes.org>,
sj38.park@gmail.com, alexander.h.duyck@linux.intel.com,
Jann Horn <jannh@google.com>
Subject: Re: [PATCH v6 6/7] mm/madvise: employ mmget_still_valid for write lock
Date: Mon, 2 Mar 2020 08:32:44 -0800 [thread overview]
Message-ID: <CAJuCfpE++EUbmhmr6+iutFk5Nd3teXy5Xr0y735LP25ciNKKcQ@mail.gmail.com> (raw)
In-Reply-To: <20200302073332.gn7lvhxmmv5pupyq@butterfly.localdomain>
On Sun, Mar 1, 2020 at 11:33 PM Oleksandr Natalenko
<oleksandr@redhat.com> wrote:
>
> Hello.
>
> On Fri, Feb 28, 2020 at 03:19:55PM -0800, Suren Baghdasaryan wrote:
> > On Tue, Feb 18, 2020 at 5:44 PM Minchan Kim <minchan@kernel.org> wrote:
> > >
> > > From: Oleksandr Natalenko <oleksandr@redhat.com>
> > >
> > > Do the very same trick as we already do since 04f5866e41fb. KSM hints
> > > will require locking mmap_sem for write since they modify vm_flags, so
> > > for remote KSM hinting this additional check is needed.
> > >
> > > Signed-off-by: Oleksandr Natalenko <oleksandr@redhat.com>
> > > Signed-off-by: Minchan Kim <minchan@kernel.org>
> > > ---
> > > mm/madvise.c | 3 +++
> > > 1 file changed, 3 insertions(+)
> > >
> > > diff --git a/mm/madvise.c b/mm/madvise.c
> > > index f6d9b9e66243..c55a18fe71f9 100644
> > > --- a/mm/madvise.c
> > > +++ b/mm/madvise.c
> > > @@ -1118,6 +1118,8 @@ int do_madvise(struct task_struct *target_task, struct mm_struct *mm,
> > > if (write) {
> > > if (down_write_killable(&mm->mmap_sem))
> > > return -EINTR;
> > > + if (current->mm != mm && !mmget_still_valid(mm))
> >
> > mmget_still_valid() seems pretty light-weight, so why not just use
> > that without checking that the mm belongs to the current process
> > first?
>
> I'd keep the checks separate to a) do not functionally change current->mm
> == mm case; b) clearly separate the intention to call
> mmget_still_valid() only for remote access (using mmget_still_valid()
> for current->mm == mm does not make any sense here, IMO, since there's
> no possibility of expecting a core dump at this point); c) ease the job for
> reviewer once mmget_still_valid() is scheduled to be removed (I hope it
> eventually goes away indeed).
>
Makes sense. Thanks!
> >
> > > + goto skip_mm;
> > > } else {
> > > down_read(&mm->mmap_sem);
> > > }
> > > @@ -1169,6 +1171,7 @@ int do_madvise(struct task_struct *target_task, struct mm_struct *mm,
> > > }
> > > out:
> > > blk_finish_plug(&plug);
> > > +skip_mm:
> > > if (write)
> > > up_write(&mm->mmap_sem);
> > > else
> > > --
> > > 2.25.0.265.gbab2e86ba0-goog
> > >
> >
>
> --
> Best regards,
> Oleksandr Natalenko (post-factum)
> Principal Software Maintenance Engineer
>
Reviewed-by: Suren Baghdasaryan <surenb@google.com>
next prev parent reply other threads:[~2020-03-02 16:32 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-19 1:44 [PATCH v6 0/7] introduce memory hinting API for external process Minchan Kim
2020-02-19 1:44 ` [PATCH v6 1/7] mm: pass task and mm to do_madvise Minchan Kim
2020-02-28 22:15 ` Suren Baghdasaryan
2020-02-19 1:44 ` [PATCH v6 2/7] mm: introduce external memory hinting API Minchan Kim
2020-02-20 19:13 ` kbuild test robot
2020-02-20 21:15 ` Minchan Kim
2020-02-20 21:21 ` Minchan Kim
2020-02-28 22:14 ` Suren Baghdasaryan
2020-03-02 19:18 ` Minchan Kim
2020-02-20 20:48 ` kbuild test robot
2020-02-19 1:44 ` [PATCH v6 3/7] mm: check fatal signal pending of target process Minchan Kim
2020-02-28 22:20 ` Suren Baghdasaryan
2020-02-19 1:44 ` [PATCH v6 4/7] pid: move pidfd_get_pid function to pid.c Minchan Kim
2020-02-28 22:22 ` Suren Baghdasaryan
2020-02-19 1:44 ` [PATCH v6 5/7] mm: support both pid and pidfd for process_madvise Minchan Kim
2020-02-28 22:41 ` Suren Baghdasaryan
2020-03-02 19:23 ` Minchan Kim
2020-03-02 19:38 ` Suren Baghdasaryan
2020-02-19 1:44 ` [PATCH v6 6/7] mm/madvise: employ mmget_still_valid for write lock Minchan Kim
2020-02-28 23:19 ` Suren Baghdasaryan
2020-03-02 7:33 ` Oleksandr Natalenko
2020-03-02 16:32 ` Suren Baghdasaryan [this message]
2020-02-19 1:44 ` [PATCH v6 7/7] mm/madvise: allow KSM hints for remote API Minchan Kim
2020-02-19 20:01 ` [PATCH v6 0/7] introduce memory hinting API for external process Andrew Morton
2020-02-19 21:05 ` Suren Baghdasaryan
2020-02-19 22:32 ` Minchan Kim
2020-02-19 22:51 ` Brian Geffon
2020-02-20 9:16 ` SeongJae Park
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