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[209.85.220.65]) by mx.google.com with SMTPS id x18sor1309307ybq.56.2019.07.16.16.36.30 for (Google Transport Security); Tue, 16 Jul 2019 16:36:30 -0700 (PDT) Received-SPF: pass (google.com: domain of shakeelb@google.com designates 209.85.220.65 as permitted sender) client-ip=209.85.220.65; Authentication-Results: mx.google.com; dkim=pass header.i=@google.com header.s=20161025 header.b=lpuf1b2g; spf=pass (google.com: domain of shakeelb@google.com designates 209.85.220.65 as permitted sender) smtp.mailfrom=shakeelb@google.com; dmarc=pass (p=REJECT sp=REJECT dis=NONE) header.from=google.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc:content-transfer-encoding; bh=3DvRpKoCvAYwziHYtBccHcC1dSVXuaUnbOKo+S/X11k=; b=lpuf1b2gx/aUfClr5+KNJP5DLR09tUGD2JrJWQQtk8qjh12G0y4YpXbKoYRphoyu36 T6b27L37CHAQK6fO5kxUwb9DSyp6FRLDUAgcYc1myXa5RLsmBiz8Iq+cuZz+5n5DSeIa 1NhF8rvjEFLKh76hIYXvkjknfOOfyvH+9ruEq7cQYoWanb76cFT5gWr5Octl5yMn8zsD 45n92fDTMCSLUJwho4HP0+o6zXY55O+Dm1bmEGxjUp/6W7hu2CwOKIuYddkzVdLlB1TX XlCETh/NQ1NUAJ2QRCdYkgn9O25OGAe/dzSemA+2ln0Cssb+Dd/NLofB0g87ivWA8XJv RdAw== X-Google-Smtp-Source: APXvYqyEqS+8CgKjlAnskwqJ647ZLgnRuugIZRb3TtL/lsuMBFVBrm2lRsHmMt27Q2DG8Rz4wuaf7udpSd7BK3zcw4M= X-Received: by 2002:a25:9903:: with SMTP id z3mr22033869ybn.293.1563320189587; Tue, 16 Jul 2019 16:36:29 -0700 (PDT) MIME-Version: 1.0 References: <1562795006.8510.19.camel@lca.pw> <1562879229.8510.24.camel@lca.pw> <1563225798.4610.5.camel@lca.pw> <5c853e6e-6367-d83c-bb97-97cd67320126@linux.alibaba.com> <8A64D551-FF5B-4068-853E-9E31AF323517@lca.pw> In-Reply-To: From: Shakeel Butt Date: Tue, 16 Jul 2019 16:36:18 -0700 Message-ID: Subject: Re: list corruption in deferred_split_scan() To: Yang Shi , Kirill Tkhai , Vladimir Davydov , Hugh Dickins , Michal Hocko , Johannes Weiner , Roman Gushchin Cc: Qian Cai , "Kirill A. Shutemov" , Andrew Morton , Linux MM , LKML Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable 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: Adding related people. The thread starts at: http://lkml.kernel.org/r/1562795006.8510.19.camel@lca.pw On Mon, Jul 15, 2019 at 8:01 PM Yang Shi wrote= : > > > > On 7/15/19 6:36 PM, Qian Cai wrote: > > > >> On Jul 15, 2019, at 8:22 PM, Yang Shi wro= te: > >> > >> > >> > >> On 7/15/19 2:23 PM, Qian Cai wrote: > >>> On Fri, 2019-07-12 at 12:12 -0700, Yang Shi wrote: > >>>>> Another possible lead is that without reverting the those commits b= elow, > >>>>> kdump > >>>>> kernel would always also crash in shrink_slab_memcg() at this line, > >>>>> > >>>>> map =3D rcu_dereference_protected(memcg->nodeinfo[nid]->shrinker_ma= p, true); > >>>> This looks a little bit weird. It seems nodeinfo[nid] is NULL? I did= n't > >>>> think of where nodeinfo was freed but memcg was still online. Maybe = a > >>>> check is needed: > >>> Actually, "memcg" is NULL. > >> It sounds weird. shrink_slab() is called in mem_cgroup_iter which does= pin the memcg. So, the memcg should not go away. > > Well, the commit =E2=80=9Cmm: shrinker: make shrinker not depend on mem= cg kmem=E2=80=9D changed this line in shrink_slab_memcg(), > > > > - if (!memcg_kmem_enabled() || !mem_cgroup_online(memcg)) > > + if (!mem_cgroup_online(memcg)) > > return 0; > > > > Since the kdump kernel has the parameter =E2=80=9Ccgroup_disable=3Dmemo= ry=E2=80=9D, shrink_slab_memcg() will no longer be able to handle NULL memc= g from mem_cgroup_iter() as, > > > > if (mem_cgroup_disabled()) > > return NULL; > > Aha, yes. memcg_kmem_enabled() implicitly checks !mem_cgroup_disabled(). > Thanks for figuring this out. I think we need add mem_cgroup_dsiabled() > check before calling shrink_slab_memcg() as below: > > diff --git a/mm/vmscan.c b/mm/vmscan.c > index a0301ed..2f03c61 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -701,7 +701,7 @@ static unsigned long shrink_slab(gfp_t gfp_mask, int > nid, > unsigned long ret, freed =3D 0; > struct shrinker *shrinker; > > - if (!mem_cgroup_is_root(memcg)) > + if (!mem_cgroup_disabled() && !mem_cgroup_is_root(memcg)) > return shrink_slab_memcg(gfp_mask, nid, memcg, priority)= ; > > if (!down_read_trylock(&shrinker_rwsem)) > We were seeing unneeded oom-kills on kernels with "cgroup_disabled=3Dmemory" and Yang's patch series basically expose the bug to crash. I think the commit aeed1d325d42 ("mm/vmscan.c: generalize shrink_slab() calls in shrink_node()") missed the case for "cgroup_disabled=3Dmemory". However I am surprised that root_mem_cgroup is allocated even for "cgroup_disabled=3Dmemory" and it seems like css_alloc() is called even before checking if the corresponding controller is disabled. Yang, can you please send the above change with signed-off and CC to stable as well? thanks, Shakeel