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[217.140.110.172]) by mx.google.com with ESMTP id o10si28215109ejx.110.2019.08.06.01.31.46 for ; Tue, 06 Aug 2019 01:31:46 -0700 (PDT) Received-SPF: pass (google.com: domain of anshuman.khandual@arm.com designates 217.140.110.172 as permitted sender) client-ip=217.140.110.172; Authentication-Results: mx.google.com; spf=pass (google.com: domain of anshuman.khandual@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=anshuman.khandual@arm.com Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 6D59F337; Tue, 6 Aug 2019 01:31:45 -0700 (PDT) Received: from [10.163.1.69] (unknown [10.163.1.69]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 6B3763F706; Tue, 6 Aug 2019 01:31:42 -0700 (PDT) Subject: Re: [PATCH V2] fork: Improve error message for corrupted page tables To: Vlastimil Babka , Sai Praneeth Prakhya , linux-kernel@vger.kernel.org, linux-mm@kvack.org Cc: dave.hansen@intel.com, Ingo Molnar , Peter Zijlstra , Andrew Morton References: <3ef8a340deb1c87b725d44edb163073e2b6eca5a.1565059496.git.sai.praneeth.prakhya@intel.com> <5ba88460-cf01-3d53-6d13-45e650b4eacd@suse.cz> From: Anshuman Khandual Message-ID: <926d50ce-4742-0ae7-474c-ef561fe23cdd@arm.com> Date: Tue, 6 Aug 2019 14:02:26 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <5ba88460-cf01-3d53-6d13-45e650b4eacd@suse.cz> Content-Type: text/plain; charset=utf-8 Content-Language: en-US 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 08/06/2019 01:23 PM, Vlastimil Babka wrote: > > On 8/6/19 5:05 AM, 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 >> >> Also, change print function (from printk(KERN_ALERT, ..) to pr_alert()) so >> that it matches the other print statement. >> >> Cc: Ingo Molnar >> Cc: Vlastimil Babka >> Cc: Peter Zijlstra >> Cc: Andrew Morton >> Cc: Anshuman Khandual >> Acked-by: Dave Hansen >> Suggested-by: Dave Hansen >> Signed-off-by: Sai Praneeth Prakhya > > Acked-by: Vlastimil Babka > > I would also add something like this to reduce risk of breaking it in the > future: > > ----8<---- > diff --git a/include/linux/mm_types_task.h b/include/linux/mm_types_task.h > index d7016dcb245e..a6f83cbe4603 100644 > --- a/include/linux/mm_types_task.h > +++ b/include/linux/mm_types_task.h > @@ -36,6 +36,9 @@ struct vmacache { > struct vm_area_struct *vmas[VMACACHE_SIZE]; > }; > > +/* > + * When touching this, update also resident_page_types in kernel/fork.c > + */ > enum { > MM_FILEPAGES, /* Resident file mapping pages */ > MM_ANONPAGES, /* Resident anonymous pages */ > Agreed and with that Reviewed-by: Anshuman Khandual