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Fri, 06 Mar 2020 05:03:05 -0800 (PST) Received: from localhost ([2001:470:5b39:28:1273:be38:bc73:5c36]) by smtp.gmail.com with ESMTPSA id u8sm4029986wrn.69.2020.03.06.05.03.03 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 06 Mar 2020 05:03:03 -0800 (PST) Date: Fri, 6 Mar 2020 14:03:03 +0100 From: Oleksandr Natalenko To: Vlastimil Babka Cc: Minchan Kim , Andrew Morton , LKML , linux-mm , linux-api@vger.kernel.org, Suren Baghdasaryan , Tim Murray , Daniel Colascione , Sandeep Patil , Sonny Rao , Brian Geffon , Michal Hocko , Johannes Weiner , Shakeel Butt , John Dias , Joel Fernandes , Jann Horn , alexander.h.duyck@linux.intel.com, sj38.park@gmail.com Subject: Re: [PATCH v7 6/7] mm/madvise: employ mmget_still_valid for write lock Message-ID: <20200306130303.kztv64f52qknxb6k@butterfly.localdomain> References: <20200302193630.68771-1-minchan@kernel.org> <20200302193630.68771-7-minchan@kernel.org> MIME-Version: 1.0 In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: quoted-printable Content-Disposition: inline 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: Hello. On Fri, Mar 06, 2020 at 01:52:07PM +0100, Vlastimil Babka wrote: > > diff --git a/mm/madvise.c b/mm/madvise.c > > index e794367f681e..e77c6c1fad34 100644 > > --- a/mm/madvise.c > > +++ b/mm/madvise.c > > @@ -1118,6 +1118,8 @@ int do_madvise(struct task_struct *target_task, s= truct mm_struct *mm, > > =09if (write) { > > =09=09if (down_write_killable(&mm->mmap_sem)) > > =09=09=09return -EINTR; > > +=09=09if (current->mm !=3D mm && !mmget_still_valid(mm)) > > +=09=09=09goto skip_mm; >=20 > This will return 0, is that correct? Shoudln't there be a similar error e= .g. as > when finding the task by pid fails (-ESRCH ?), because IIUC the task here= is > going away and dumping the core? Yeah. Something like this then: =3D=3D=3D diff --git a/mm/madvise.c b/mm/madvise.c index 48d1da08c160..7ed2f4d13924 100644 --- a/mm/madvise.c +++ b/mm/madvise.c @@ -1122,6 +1122,10 @@ int do_madvise(struct task_struct *target_task, stru= ct mm_struct *mm, =09if (write) { =09=09if (down_write_killable(&mm->mmap_sem)) =09=09=09return -EINTR; +=09=09if (current->mm !=3D mm && !mmget_still_valid(mm)) { +=09=09=09error =3D -ESRCH; +=09=09=09goto skip_mm; +=09=09} =09} else { =09=09down_read(&mm->mmap_sem); =09} @@ -1173,6 +1177,7 @@ int do_madvise(struct task_struct *target_task, struc= t mm_struct *mm, =09} out: =09blk_finish_plug(&plug); +skip_mm: =09if (write) =09=09up_write(&mm->mmap_sem); =09else =3D=3D=3D ? >=20 > > =09} else { > > =09=09down_read(&mm->mmap_sem); > > =09} > > @@ -1169,6 +1171,7 @@ int do_madvise(struct task_struct *target_task, s= truct mm_struct *mm, > > =09} > > out: > > =09blk_finish_plug(&plug); > > +skip_mm: > > =09if (write) > > =09=09up_write(&mm->mmap_sem); > > =09else > >=20 >=20 --=20 Best regards, Oleksandr Natalenko (post-factum) Principal Software Maintenance Engineer