From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pj1-f53.google.com (mail-pj1-f53.google.com [209.85.216.53]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 49A8E7C for ; Tue, 14 Jun 2022 03:19:31 +0000 (UTC) Received: by mail-pj1-f53.google.com with SMTP id q12-20020a17090a304c00b001e2d4fb0eb4so10577058pjl.4 for ; Mon, 13 Jun 2022 20:19:31 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chromium.org; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=7L8e1Wz/Bd9z7iLzaFmqZHzg9hGkFUKT87XneuMBC4s=; b=UXGxXFisJTDA5eg/7J+MzK1OfxHBFi3fX5Hr9jfiVqSYvKefez4KuMeV9V2EJcHwyS u0p2ak8L1LS9b0xqmMzO4boRwj+o88ckA/SQhGa0etdFy4Sb+OYvBc1GdtRO9SKYMoLV E/bBmZBENCoJN1eexVato9L4Ks2NmoR5u9fRU= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=7L8e1Wz/Bd9z7iLzaFmqZHzg9hGkFUKT87XneuMBC4s=; b=W23Cct04lbY1Q3bhvHUeC4asw4rij/4MbF7e6yzR5QO7D8QVI6579YWIVZZvi87SNX GCOIV558l5RBLf8qcka/hAucysFydDemC1rXKzCjBdoK61Bdl9nDtzMSKeyJA9YWwU/+ mVlVWTSql7VXmfHzecF2UOSfPyWzY97gsaxsZXDMsmPRdHypAA2IynESsI2HuLUo3mVX 1KsiIH5utghoVMujkm/Nh8FBYflMCGZWo/RjY03YaSiCkjwDmp5x69DQWnXkIs5g4xEV bABVPaYNTKKxPnn4V5NJ3otZhqQL1vuXAHFwDVNbTJ0nJuQ0IlCxaRr6o2AE8eWiZP4q erYw== X-Gm-Message-State: AJIora/KrwoPNjkLFdzT0nlNjPI4tHaq5dlqbngmHkWy9lzxfL8F6X7u gFXE0mWn12dIyetEZB/oIaW59g== X-Google-Smtp-Source: AGRyM1vWB6bubOckC1eBAZ912PtyRJ9dDViWlYRgpIAHNDPo8sztccizLgEYqmphzjIE3Rz/945vWA== X-Received: by 2002:a17:90a:c7cf:b0:1e8:2b77:7835 with SMTP id gf15-20020a17090ac7cf00b001e82b777835mr2163700pjb.109.1655176770633; Mon, 13 Jun 2022 20:19:30 -0700 (PDT) Received: from google.com ([2401:fa00:8f:203:580a:28cf:a82b:5610]) by smtp.gmail.com with ESMTPSA id b6-20020a170902650600b0015ee985999dsm5905819plk.97.2022.06.13.20.19.27 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 13 Jun 2022 20:19:29 -0700 (PDT) Date: Tue, 14 Jun 2022 12:19:24 +0900 From: Sergey Senozhatsky To: Minchan Kim Cc: Sergey Senozhatsky , umgwanakikbuti@gmail.com, bigeasy@linutronix.de, Naresh Kamboju , open list , linux-fsdevel@vger.kernel.org, Linux ARM , "open list:KERNEL SELFTEST FRAMEWORK" , linux-block , regressions@lists.linux.dev, Jens Axboe , Nitin Gupta Subject: Re: qemu-arm: zram: mkfs.ext4 : Unable to handle kernel NULL pointer dereference at virtual address 00000140 Message-ID: References: Precedence: bulk X-Mailing-List: regressions@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On (22/06/13 09:49), Minchan Kim wrote: > > Many thanks for the tests. > > > > Quite honestly I was hoping that the patch would not help :) Well, ok, > > we now know that it's mapping area lock and the lockdep part of its > > memory is zero-ed out. The question is - "why?" It really should not > > be zeroed out. > > Ccing Mike and Sebastian who are author/expert of the culprit patch > > Naresh found zsmalloc crashed on the testing [1] and confirmed > that Sergey's patch[2] fixed the problem. > However, I don't understand why we need reinit the local_lock > on cpu_up handler[3]. > > Could you guys shed some light? My guess is that it's either something very specific to Naresh's arch/config or a bug somewhere, which memset() per-CPU memory. Not sure how to track it down. KASAN maybe? We certainly don't expect that static DEFINE_PER_CPU(struct mapping_area, zs_map_area) = { .lock = INIT_LOCAL_LOCK(lock), }; would produce un-initialized dep_map. So I guess we start off with a valid per-CPU lock, but then it somehow gets zeroed-out.