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Date: Mon, 2 Mar 2020 08:33:32 +0100 From: Oleksandr Natalenko <oleksandr@...hat.com> To: Suren Baghdasaryan <surenb@...gle.com> Cc: Minchan Kim <minchan@...nel.org>, Andrew Morton <akpm@...ux-foundation.org>, LKML <linux-kernel@...r.kernel.org>, linux-mm <linux-mm@...ck.org>, linux-api@...r.kernel.org, Tim Murray <timmurray@...gle.com>, Daniel Colascione <dancol@...gle.com>, Sandeep Patil <sspatil@...gle.com>, Sonny Rao <sonnyrao@...gle.com>, Brian Geffon <bgeffon@...gle.com>, Michal Hocko <mhocko@...e.com>, Johannes Weiner <hannes@...xchg.org>, Shakeel Butt <shakeelb@...gle.com>, John Dias <joaodias@...gle.com>, Joel Fernandes <joel@...lfernandes.org>, sj38.park@...il.com, alexander.h.duyck@...ux.intel.com, Jann Horn <jannh@...gle.com> Subject: Re: [PATCH v6 6/7] mm/madvise: employ mmget_still_valid for write lock 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@...nel.org> wrote: > > > > From: Oleksandr Natalenko <oleksandr@...hat.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@...hat.com> > > Signed-off-by: Minchan Kim <minchan@...nel.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). > > > + 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
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