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[217.140.110.172]) by mx.google.com with ESMTP id v30si21278616ejk.208.2019.07.31.22.48.06 for ; Wed, 31 Jul 2019 22:48:06 -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 DC921337; Wed, 31 Jul 2019 22:48:05 -0700 (PDT) Received: from [10.163.1.81] (unknown [10.163.1.81]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 0BE013F694; Wed, 31 Jul 2019 22:50:07 -0700 (PDT) Subject: Re: [PATCH] fork: Improve error message for corrupted page tables To: Sai Praneeth Prakhya , linux-kernel@vger.kernel.org, linux-mm@kvack.org Cc: dave.hansen@intel.com, Ingo Molnar , Peter Zijlstra , Andrew Morton References: <20190730221820.7738-1-sai.praneeth.prakhya@intel.com> From: Anshuman Khandual Message-ID: <56ad91b8-1ea0-6736-5bc5-eea0ced01054@arm.com> Date: Thu, 1 Aug 2019 11:18:38 +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: <20190730221820.7738-1-sai.praneeth.prakhya@intel.com> 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 07/31/2019 03:48 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). Hence, improve the > error message so that it's more informative. The loop index in check_mm() also happens to be the index in rss_stat[] which represents individual memory type stats. But you are right, index value here in the print does not make any sense. > > 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 Yes, this is definitely better. > > Cc: Ingo Molnar > Cc: Peter Zijlstra > Cc: Andrew Morton > Suggested-by/Acked-by: Dave Hansen Though I am not sure, should the above be two separate lines instead ? > Signed-off-by: Sai Praneeth Prakhya > --- > include/linux/mm_types_task.h | 7 +++++++ > kernel/fork.c | 4 ++-- > 2 files changed, 9 insertions(+), 2 deletions(-) > > diff --git a/include/linux/mm_types_task.h b/include/linux/mm_types_task.h > index d7016dcb245e..881f4ea3a1b5 100644 > --- a/include/linux/mm_types_task.h > +++ b/include/linux/mm_types_task.h > @@ -44,6 +44,13 @@ enum { > NR_MM_COUNTERS > }; > > +static const char * const resident_page_types[NR_MM_COUNTERS] = { > + "MM_FILEPAGES", > + "MM_ANONPAGES", > + "MM_SWAPENTS", > + "MM_SHMEMPAGES", > +}; Should index them to match respective typo macros. [MM_FILEPAGES] = "MM_FILEPAGES", [MM_ANONPAGES] = "MM_ANONPAGES", [MM_SWAPENTS] = "MM_SWAPENTS", [MM_SHMEMPAGES] = "MM_SHMEMPAGES", > + > #if USE_SPLIT_PTE_PTLOCKS && defined(CONFIG_MMU) > #define SPLIT_RSS_COUNTING > /* per-thread cached information, */ > diff --git a/kernel/fork.c b/kernel/fork.c > index 2852d0e76ea3..6aef5842d4e0 100644 > --- a/kernel/fork.c > +++ b/kernel/fork.c > @@ -649,8 +649,8 @@ static void check_mm(struct mm_struct *mm) > long x = atomic_long_read(&mm->rss_stat.count[i]); > > if (unlikely(x)) > - printk(KERN_ALERT "BUG: Bad rss-counter state " > - "mm:%p idx:%d val:%ld\n", mm, i, x); > + pr_alert("BUG: Bad rss-counter state mm:%p type:%s val:%ld\n", > + mm, resident_page_types[i], x); It changes the print function as well, though very minor change but perhaps mention that in the commit message ?