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[192.55.52.115]) by mx.google.com with ESMTPS id v4si42272856plp.212.2019.08.06.14.25.04 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 06 Aug 2019 14:25:04 -0700 (PDT) Received-SPF: pass (google.com: domain of sai.praneeth.prakhya@intel.com designates 192.55.52.115 as permitted sender) client-ip=192.55.52.115; Authentication-Results: mx.google.com; spf=pass (google.com: domain of sai.praneeth.prakhya@intel.com designates 192.55.52.115 as permitted sender) smtp.mailfrom=sai.praneeth.prakhya@intel.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=intel.com X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga007.jf.intel.com ([10.7.209.58]) by fmsmga103.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 06 Aug 2019 14:25:04 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.64,353,1559545200"; d="scan'208";a="165111737" Received: from sai-dev-mach.sc.intel.com ([143.183.140.153]) by orsmga007.jf.intel.com with ESMTP; 06 Aug 2019 14:25:03 -0700 Message-ID: <25c28a6e5137aa396bc13a2f581566e13e98f45e.camel@intel.com> Subject: Re: [PATCH V2] fork: Improve error message for corrupted page tables From: Sai Praneeth Prakhya To: Michal Hocko Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, dave.hansen@intel.com, Ingo Molnar , Vlastimil Babka , Peter Zijlstra , Andrew Morton , Anshuman Khandual Date: Tue, 06 Aug 2019 14:21:54 -0700 In-Reply-To: <20190806083605.GA19060@dhcp22.suse.cz> References: <3ef8a340deb1c87b725d44edb163073e2b6eca5a.1565059496.git.sai.praneeth.prakhya@intel.com> <20190806083605.GA19060@dhcp22.suse.cz> Content-Type: text/plain; charset="UTF-8" User-Agent: Evolution 3.30.5-0ubuntu0.18.10.1 MIME-Version: 1.0 Content-Transfer-Encoding: 7bit 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 Tue, 2019-08-06 at 10:36 +0200, Michal Hocko wrote: > On Mon 05-08-19 20:05:27, Sai Praneeth Prakhya wrote: > > When a user process exits, the kernel cleans up the mm_struct of the user > > process and during cleanup, check_mm() checks the page tables of the user > > process for corruption (E.g: unexpected page flags set/cleared). For > > corrupted page tables, the error message printed by check_mm() isn't very > > clear as it prints the loop index instead of page table type (E.g: > > Resident > > file mapping pages vs Resident shared memory pages). The loop index in > > check_mm() is used to index rss_stat[] which represents individual memory > > type stats. Hence, instead of printing index, print memory type, thereby > > improving error message. > > > > Without patch: > > -------------- > > [ 204.836425] mm/pgtable-generic.c:29: bad p4d > > 0000000089eb4e92(800000025f941467) > > [ 204.836544] BUG: Bad rss-counter state mm:00000000f75895ea idx:0 val:2 > > [ 204.836615] BUG: Bad rss-counter state mm:00000000f75895ea idx:1 val:5 > > [ 204.836685] BUG: non-zero pgtables_bytes on freeing mm: 20480 > > > > With patch: > > ----------- > > [ 69.815453] mm/pgtable-generic.c:29: bad p4d > > 0000000084653642(800000025ca37467) > > [ 69.815872] BUG: Bad rss-counter state mm:00000000014a6c03 > > type:MM_FILEPAGES val:2 > > [ 69.815962] BUG: Bad rss-counter state mm:00000000014a6c03 > > type:MM_ANONPAGES val:5 > > [ 69.816050] BUG: non-zero pgtables_bytes on freeing mm: 20480 > > I like this. On any occasion I am investigating an issue with an rss > inbalance I have to go back to kernel sources to see which pte type that > is. > Hopefully, this patch will be useful to you the next time you run into any rss imbalance issues. > > Also, change print function (from printk(KERN_ALERT, ..) to pr_alert()) so > > that it matches the other print statement. > > good change as well. Maybe we should also lower the loglevel (in a > separate patch) as well. While this is not nice because we are > apparently leaking memory behind it shouldn't be really critical enough > to jump on normal consoles. Ya.. I think, probably could be lowered to pr_err() or pr_warn(). Regards, Sai