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[209.85.220.65]) by mx.google.com with SMTPS id p124sor10092011ywp.103.2019.06.19.16.04.40 for (Google Transport Security); Wed, 19 Jun 2019 16:04:40 -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=t5CyOJNf; 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; bh=NbzMOyrZckNlP/Lcg+Lm/vM3zrC2t8DPpb83xlh9FiI=; b=t5CyOJNfaac+Q7sPzpACyPTDx6EHsMBAXAnNFHc1O5tDZWecDaCzf1vYTuyz7Zjf/e 67AVLo3wFwFhYh4mwpzgD+9UNuTSphgseGd0AVOtn7iOtYOElLcQ3s+WX4gwDSQUJSAG kHzUBPWbM3Dmo4KyNNeKLuRTTau5zxBm1pYUE8IUgg96i3/B0ojjp1aZCvK8b5YvIrRq 3y/D3kCzgimUMVAjolJtiirGA8S5lSRCCmJdB1ggTynoPqquMl1gDOrFf2Hao69SK3nD qqRIODa4r7NbdVpNTrP+mSFxZxA2I3Lap/PkRe7pPMQAA9C50Yxp8L3JthprklpEeTg/ Qmtw== X-Google-Smtp-Source: APXvYqwwLc9GbuN1yski600QDsOdlXMt97I/+eg7SO2Z7GQo/t8DI3dWtHIREvPeuOmKIK1eoWONOQDWPdZIfMaHZBs= X-Received: by 2002:a81:a55:: with SMTP id 82mr37722007ywk.205.1560985479831; Wed, 19 Jun 2019 16:04:39 -0700 (PDT) MIME-Version: 1.0 References: In-Reply-To: From: Shakeel Butt Date: Wed, 19 Jun 2019 16:04:28 -0700 Message-ID: Subject: Re: memcg/kmem panics To: Dave Hansen Cc: Johannes Weiner , Michal Hocko , Vladimir Davydov , Cgroups , Linux MM , LKML , "Williams, Dan J" 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 Wed, Jun 19, 2019 at 3:50 PM Dave Hansen wrote: > > I have a bit of a grievance to file. :) > > I'm seeing "Cannot create slab..." panic()s coming from > kmem_cache_open() when trying to create memory cgroups on a Fedora > system running 5.2-rc's. The panic()s happen when failing to create > memcg-specific slabs because the memcg code passes through the > root_cache->flags, which can include SLAB_PANIC. > > I haven't tracked down the root cause yet, or where this behavior > started. But, the end-user experience is that systemd tries to create a > cgroup and ends up with a kernel panic. That's rather sad, especially > for the poor sod that's trying to debug it. > > Should memcg_create_kmem_cache() be, perhaps filtering out SLAB_PANIC > from root_cache->flags, for instance? That might make the system a bit > less likely to turn into a doorstop if and when something goes mildly > wrong. I've hacked out the panic()s and the system actually seems to > boot OK. You must be using CONFIG_SLUB and I see that in kmem_cache_open() in SLUB doing a SLAB_PANIC check. I think we should remove that altogether from SLUB as SLAB does not do this and failure in memcg kmem cache creation can and should be handled gracefully. I can send a patch to remove that check. Shakeel