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d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=0RBtUKeaPvU/GzP+jMS3Dsfo2rIt9YBehMmbHfwGd7A=; b=RFVnCfHGgiinhJ63Xog3uekB2evUIcUGxGUZfomOwC1IZSxB8DXnkJk+EfHFk8Ix0x DjQJo/YwdESIr36AE0pJfWAScAxBsoT/k1W5TGB2DEpHk+e7LGRVoOkvmUYiegfJD/dA 8xNIGbIpj0yyM0e6GVKwQaXiBL2Oxk3Y7cmuqWlhqgvqYaZBaIiCekQZzZSGZaG9z7sy kK09J5PV0ctGU7nQgG50d22AtZkzGd0/hHuTd3T4+L6I4bT2Tqcc1SXQWFDN1AgFSEqK 01ZPTBWtyVgZmtpmNcMGWEr/Ilcv2CTZV5gv76QoQv3w2sTaexCj4EI1OKrqTwA8qtuX 1miA== X-Gm-Message-State: AOAM533B2kaFMbfIrVnZsewR00zVNUctMdIoZeAbee+DUVaFMaLPWm6g Y36b3b7o5yXl3L4gD2AhNjIjeH/AefcS+NboblK06Q== X-Google-Smtp-Source: ABdhPJw6elyMIoCPQlMD7L22PrIxSIlxVRceE737acKSgpuGoNsk6wo48ZXOON51AoZrJvlkpaizVjpKm2+u57GQA3g= X-Received: by 2002:a17:906:c51:: with SMTP id t17mr4830318ejf.523.1606855363156; Tue, 01 Dec 2020 12:42:43 -0800 (PST) MIME-Version: 1.0 References: <20201201022412.GG4327@casper.infradead.org> In-Reply-To: <20201201022412.GG4327@casper.infradead.org> From: Dan Williams Date: Tue, 1 Dec 2020 12:42:39 -0800 Message-ID: Subject: Re: mapcount corruption regression To: Matthew Wilcox Cc: "Shutemov, Kirill" , Linux Kernel Mailing List , Linux MM , linux-nvdimm , Vlastimil Babka 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 Mon, Nov 30, 2020 at 6:24 PM Matthew Wilcox wrote: > > On Mon, Nov 30, 2020 at 05:20:25PM -0800, Dan Williams wrote: > > Kirill, Willy, compound page experts, > > > > I am seeking some debug ideas about the following splat: > > > > BUG: Bad page state in process lt-pmem-ns pfn:121a12 > > page:0000000051ef73f7 refcount:0 mapcount:-1024 > > mapping:0000000000000000 index:0x0 pfn:0x121a12 > > Mapcount of -1024 is the signature of: > > #define PG_guard 0x00000400 Oh, thanks for that. I overlooked how mapcount is overloaded. Although in v5.10-rc4 that value is: #define PG_table 0x00000400 > > (the bits are inverted, so this turns into 0xfffffbff which is reported > as -1024) > > I assume you have debug_pagealloc enabled? Added it, but no extra spew. I'll dig a bit more on how PG_table is not being cleared in this case.