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[213.175.37.10]) by smtp.gmail.com with ESMTPSA id c4sm14145502wml.7.2020.03.01.23.33.32 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 01 Mar 2020 23:33:33 -0800 (PST) Date: Mon, 2 Mar 2020 08:33:32 +0100 From: Oleksandr Natalenko To: Suren Baghdasaryan 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 Subject: Re: [PATCH v6 6/7] mm/madvise: employ mmget_still_valid for write lock Message-ID: <20200302073332.gn7lvhxmmv5pupyq@butterfly.localdomain> References: <20200219014433.88424-1-minchan@kernel.org> <20200219014433.88424-7-minchan@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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). > > > + 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