From: Anshuman Khandual <anshuman.khandual@arm.com> To: Christophe Leroy <christophe.leroy@c-s.fr>, Rong Chen <rong.a.chen@intel.com>, kernel test robot <lkp@intel.com> Cc: Ingo Molnar <mingo@kernel.org>, Andrew Morton <akpm@linux-foundation.org>, Linux Memory Management List <linux-mm@kvack.org>, LKP <lkp@lists.01.org> Subject: Re: [LKP] Re: 87c4696d57 ("mm/debug: Add tests validating architecture page .."): [ 1.395296] kernel BUG at include/linux/mm.h:2007! Date: Mon, 27 Jan 2020 13:34:50 +0530 [thread overview] Message-ID: <628ec098-9343-5b92-7bca-ad330533e828@arm.com> (raw) In-Reply-To: <1077e260-d2c3-fcc6-1150-fb46b6273db3@c-s.fr> On 01/24/2020 02:22 PM, Christophe Leroy wrote: > > > Le 24/01/2020 à 08:17, Anshuman Khandual a écrit : >> >> On 01/07/2020 12:00 PM, Rong Chen wrote: >>> >>> >>> On 1/7/20 1:57 PM, Anshuman Khandual wrote: >>>> On 12/26/2019 02:19 PM, kernel test robot wrote: >> ............................................... >> p4d_free(mm, saved_p4dp); >> pud_free(mm, saved_pudp); >> pmd_free(mm, saved_pmdp); >> pte_free(mm, saved_ptep); >> mm_dec_nr_puds(mm); >> mm_dec_nr_pmds(mm); >> mm_dec_nr_ptes(mm); >> __mmdrop(mm); >> .............................................. >> > > You should use mmdrop() instead of __mmdrop(), shouldn't you ? Yes, though I am afraid that it does not change much as mm->mm_count gets initialized to 1 through mm_alloc()->mm_init(). But will fix this next time around. Coming back to the original problem, seems like both the reported bugs are probably related and because of CONFIG_X86_PAE. On X86 PAE systems, there are these additional user and kernel PMD pages which are stored in the page table (PREALLOCATED_USER_PMDS and MAX_PREALLOCATED_PMDS). pgd_alloc() preallocate_pmds() __get_free_page() pgtable_pmd_page_ctor() pgd_prepopulate_pmd() p4d = p4d_offset(pgd, 0); pud = pud_offset(p4d, 0); pud_populate(mm, pud, pmd); /* For each pre-allocated PMD */ The test case explicitly allocates and frees intermittent level page table pages for any given vaddr. So when __mmdrop() --> pgd_free() --> mop_up_pmds() --> mop_up_one_pmd() --> pmd_free(), it tries to free some possible garbage memory (probably caused by the test case) and hits VM_BUG_ON(). The test assumes a bare bones page table to conduct the test and the PAE based page table setup violates that assumption. Will disable this test on x86 platform when CONFIG_X86_PAE is enabled. > > Christophe >
WARNING: multiple messages have this Message-ID (diff)
From: Anshuman Khandual <anshuman.khandual@arm.com> To: lkp@lists.01.org Subject: Re: 87c4696d57 ("mm/debug: Add tests validating architecture page .."): [ 1.395296] kernel BUG at include/linux/mm.h:2007! Date: Mon, 27 Jan 2020 13:34:50 +0530 [thread overview] Message-ID: <628ec098-9343-5b92-7bca-ad330533e828@arm.com> (raw) In-Reply-To: <1077e260-d2c3-fcc6-1150-fb46b6273db3@c-s.fr> [-- Attachment #1: Type: text/plain, Size: 2030 bytes --] On 01/24/2020 02:22 PM, Christophe Leroy wrote: > > > Le 24/01/2020 à 08:17, Anshuman Khandual a écrit : >> >> On 01/07/2020 12:00 PM, Rong Chen wrote: >>> >>> >>> On 1/7/20 1:57 PM, Anshuman Khandual wrote: >>>> On 12/26/2019 02:19 PM, kernel test robot wrote: >> ............................................... >> p4d_free(mm, saved_p4dp); >> pud_free(mm, saved_pudp); >> pmd_free(mm, saved_pmdp); >> pte_free(mm, saved_ptep); >> mm_dec_nr_puds(mm); >> mm_dec_nr_pmds(mm); >> mm_dec_nr_ptes(mm); >> __mmdrop(mm); >> .............................................. >> > > You should use mmdrop() instead of __mmdrop(), shouldn't you ? Yes, though I am afraid that it does not change much as mm->mm_count gets initialized to 1 through mm_alloc()->mm_init(). But will fix this next time around. Coming back to the original problem, seems like both the reported bugs are probably related and because of CONFIG_X86_PAE. On X86 PAE systems, there are these additional user and kernel PMD pages which are stored in the page table (PREALLOCATED_USER_PMDS and MAX_PREALLOCATED_PMDS). pgd_alloc() preallocate_pmds() __get_free_page() pgtable_pmd_page_ctor() pgd_prepopulate_pmd() p4d = p4d_offset(pgd, 0); pud = pud_offset(p4d, 0); pud_populate(mm, pud, pmd); /* For each pre-allocated PMD */ The test case explicitly allocates and frees intermittent level page table pages for any given vaddr. So when __mmdrop() --> pgd_free() --> mop_up_pmds() --> mop_up_one_pmd() --> pmd_free(), it tries to free some possible garbage memory (probably caused by the test case) and hits VM_BUG_ON(). The test assumes a bare bones page table to conduct the test and the PAE based page table setup violates that assumption. Will disable this test on x86 platform when CONFIG_X86_PAE is enabled. > > Christophe >
next prev parent reply other threads:[~2020-01-27 8:04 UTC|newest] Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top 2019-12-26 8:49 87c4696d57 ("mm/debug: Add tests validating architecture page .."): [ 1.395296] kernel BUG at include/linux/mm.h:2007! kernel test robot 2019-12-26 8:49 ` kernel test robot 2020-01-07 5:57 ` Anshuman Khandual 2020-01-07 5:57 ` Anshuman Khandual 2020-01-07 6:30 ` [LKP] " Rong Chen 2020-01-07 6:30 ` Rong Chen 2020-01-24 7:17 ` [LKP] " Anshuman Khandual 2020-01-24 7:17 ` Anshuman Khandual 2020-01-24 8:52 ` [LKP] " Christophe Leroy 2020-01-24 8:52 ` Christophe Leroy 2020-01-27 8:04 ` Anshuman Khandual [this message] 2020-01-27 8:04 ` Anshuman Khandual
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