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Mon, 02 Mar 2020 08:32:55 -0800 (PST) MIME-Version: 1.0 References: <20200219014433.88424-1-minchan@kernel.org> <20200219014433.88424-7-minchan@kernel.org> <20200302073332.gn7lvhxmmv5pupyq@butterfly.localdomain> In-Reply-To: <20200302073332.gn7lvhxmmv5pupyq@butterfly.localdomain> From: Suren Baghdasaryan Date: Mon, 2 Mar 2020 08:32:44 -0800 Message-ID: Subject: Re: [PATCH v6 6/7] mm/madvise: employ mmget_still_valid for write lock To: Oleksandr Natalenko Cc: Minchan Kim , Andrew Morton , LKML , linux-mm , linux-api@vger.kernel.org, Tim Murray , Daniel Colascione , Sandeep Patil , Sonny Rao , Brian Geffon , Michal Hocko , Johannes Weiner , Shakeel Butt , John Dias , Joel Fernandes , sj38.park@gmail.com, alexander.h.duyck@linux.intel.com, Jann Horn Content-Type: text/plain; charset="UTF-8" X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Sun, Mar 1, 2020 at 11:33 PM Oleksandr Natalenko 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 wrote: > > > > > > From: Oleksandr Natalenko > > > > > > 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 > > > Signed-off-by: Minchan Kim > > > --- > > > 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