From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752418AbcBLL76 (ORCPT ); Fri, 12 Feb 2016 06:59:58 -0500 Received: from e06smtp07.uk.ibm.com ([195.75.94.103]:54283 "EHLO e06smtp07.uk.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752286AbcBLL74 (ORCPT ); Fri, 12 Feb 2016 06:59:56 -0500 X-IBM-Helo: d06dlp03.portsmouth.uk.ibm.com X-IBM-MailFrom: gerald.schaefer@de.ibm.com X-IBM-RcptTo: linux-kernel@vger.kernel.org;linux-s390@vger.kernel.org Date: Fri, 12 Feb 2016 12:59:43 +0100 From: Gerald Schaefer To: "Aneesh Kumar K.V" Cc: "Kirill A. Shutemov" , "Kirill A. Shutemov" , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton , Linus Torvalds , Michael Ellerman , Benjamin Herrenschmidt , Paul Mackerras , linuxppc-dev@lists.ozlabs.org, Catalin Marinas , Will Deacon , linux-arm-kernel@lists.infradead.org, Martin Schwidefsky , Heiko Carstens , linux-s390@vger.kernel.org, Sebastian Ott Subject: Re: [BUG] random kernel crashes after THP rework on s390 (maybe also on PowerPC and ARM) Message-ID: <20160212125943.1eb2ca9d@thinkpad> In-Reply-To: <87a8n6shf2.fsf@linux.vnet.ibm.com> References: <20160211192223.4b517057@thinkpad> <20160211190942.GA10244@node.shutemov.name> <20160211205702.24f0d17a@thinkpad> <87a8n6shf2.fsf@linux.vnet.ibm.com> X-Mailer: Claws Mail 3.9.3 (GTK+ 2.24.23; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 16021211-0029-0000-0000-000005C9932D Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 12 Feb 2016 09:34:33 +0530 "Aneesh Kumar K.V" wrote: > Gerald Schaefer writes: > > > On Thu, 11 Feb 2016 21:09:42 +0200 > > "Kirill A. Shutemov" wrote: > > > >> On Thu, Feb 11, 2016 at 07:22:23PM +0100, Gerald Schaefer wrote: > >> > Hi, > >> > > >> > Sebastian Ott reported random kernel crashes beginning with v4.5-rc1 and > >> > he also bisected this to commit 61f5d698 "mm: re-enable THP". Further > >> > review of the THP rework patches, which cannot be bisected, revealed > >> > commit fecffad "s390, thp: remove infrastructure for handling splitting PMDs" > >> > (and also similar commits for other archs). > >> > > >> > This commit removes the THP splitting bit and also the architecture > >> > implementation of pmdp_splitting_flush(), which took care of the IPI for > >> > fast_gup serialization. The commit message says > >> > > >> > pmdp_splitting_flush() is not needed too: on splitting PMD we will do > >> > pmdp_clear_flush() + set_pte_at(). pmdp_clear_flush() will do IPI as > >> > needed for fast_gup > >> > > >> > The assumption that a TLB flush will also produce an IPI is wrong on s390, > >> > and maybe also on other architectures, and I thought that this was actually > >> > the main reason for having an arch-specific pmdp_splitting_flush(). > >> > > >> > At least PowerPC and ARM also had an individual implementation of > >> > pmdp_splitting_flush() that used kick_all_cpus_sync() instead of a TLB > >> > flush to send the IPI, and those were also removed. Putting the arch > >> > maintainers and mailing lists on cc to verify. > >> > > >> > On s390 this will break the IPI serialization against fast_gup, which > >> > would certainly explain the random kernel crashes, please revert or fix > >> > the pmdp_splitting_flush() removal. > >> > >> Sorry for that. > >> > >> I believe, the problem was already addressed for PowerPC: > >> > >> http://lkml.kernel.org/g/454980831-16631-1-git-send-email-aneesh.kumar@linux.vnet.ibm.com > >> > >> I think kick_all_cpus_sync() in arch-specific pmdp_invalidate() would do > >> the trick, right? > > > > Hmm, not sure about that. After pmdp_invalidate(), a pmd_none() check in > > fast_gup will still return false, because the pmd is not empty (at least > > on s390). > > Why can't we do this ? I did this for ppc64. > > void pmdp_invalidate(struct vm_area_struct *vma, unsigned long address, > pmd_t *pmdp) > { > - pmd_hugepage_update(vma->vm_mm, address, pmdp, _PAGE_PRESENT, 0); > + pmd_hugepage_update(vma->vm_mm, address, pmdp, ~0UL, 0); > Wouldn't that semantically change what pmdp_invalidate() was supposed to do? The comment before the call says "the pmd_trans_huge and pmd_trans_splitting must remain set at all times on the pmd". So, after removing pmd_trans_splitting, it seems to be necessary to at least keep pmd_trans_huge set. In your case, the pmd would be completely cleared, which may help to find it in fast_gup with pmd_none(), but I'm not sure if this would open up other problems, e.g. with concurrent page faults. But I must also admit that my THP overview got a little rusty. > >So I don't see spontaneously how it will help fast_gup to break > > out to the slow path in case of THP splitting. > > > >> > >> If yes, I'll prepare patch tomorrow (some sleep required). > >> > > > > We'll check if adding kick_all_cpus_sync() to pmdp_invalidate() helps. > > It would also be good if Martin has a look at this, he'll return on > > Monday. > > -aneesh > > -- > To unsubscribe from this list: send the line "unsubscribe linux-s390" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f49.google.com (mail-wm0-f49.google.com [74.125.82.49]) by kanga.kvack.org (Postfix) with ESMTP id A6FA56B0005 for ; Fri, 12 Feb 2016 06:59:54 -0500 (EST) Received: by mail-wm0-f49.google.com with SMTP id 128so59174675wmz.1 for ; Fri, 12 Feb 2016 03:59:54 -0800 (PST) Received: from e06smtp09.uk.ibm.com (e06smtp09.uk.ibm.com. [195.75.94.105]) by mx.google.com with ESMTPS id pi3si18762438wjb.134.2016.02.12.03.59.53 for (version=TLS1 cipher=AES128-SHA bits=128/128); Fri, 12 Feb 2016 03:59:53 -0800 (PST) Received: from localhost by e06smtp09.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Fri, 12 Feb 2016 11:59:52 -0000 Received: from b06cxnps4075.portsmouth.uk.ibm.com (d06relay12.portsmouth.uk.ibm.com [9.149.109.197]) by d06dlp03.portsmouth.uk.ibm.com (Postfix) with ESMTP id 46ADB1B08075 for ; Fri, 12 Feb 2016 12:00:04 +0000 (GMT) Received: from d06av03.portsmouth.uk.ibm.com (d06av03.portsmouth.uk.ibm.com [9.149.37.213]) by b06cxnps4075.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id u1CBxnKA14549000 for ; Fri, 12 Feb 2016 11:59:49 GMT Received: from d06av03.portsmouth.uk.ibm.com (localhost [127.0.0.1]) by d06av03.portsmouth.uk.ibm.com (8.14.4/8.14.4/NCO v10.0 AVout) with ESMTP id u1CBxluc028965 for ; Fri, 12 Feb 2016 04:59:49 -0700 Date: Fri, 12 Feb 2016 12:59:43 +0100 From: Gerald Schaefer Subject: Re: [BUG] random kernel crashes after THP rework on s390 (maybe also on PowerPC and ARM) Message-ID: <20160212125943.1eb2ca9d@thinkpad> In-Reply-To: <87a8n6shf2.fsf@linux.vnet.ibm.com> References: <20160211192223.4b517057@thinkpad> <20160211190942.GA10244@node.shutemov.name> <20160211205702.24f0d17a@thinkpad> <87a8n6shf2.fsf@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: "Aneesh Kumar K.V" Cc: "Kirill A. Shutemov" , "Kirill A. Shutemov" , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton , Linus Torvalds , Michael Ellerman , Benjamin Herrenschmidt , Paul Mackerras , linuxppc-dev@lists.ozlabs.org, Catalin Marinas , Will Deacon , linux-arm-kernel@lists.infradead.org, Martin Schwidefsky , Heiko Carstens , linux-s390@vger.kernel.org, Sebastian Ott On Fri, 12 Feb 2016 09:34:33 +0530 "Aneesh Kumar K.V" wrote: > Gerald Schaefer writes: > > > On Thu, 11 Feb 2016 21:09:42 +0200 > > "Kirill A. Shutemov" wrote: > > > >> On Thu, Feb 11, 2016 at 07:22:23PM +0100, Gerald Schaefer wrote: > >> > Hi, > >> > > >> > Sebastian Ott reported random kernel crashes beginning with v4.5-rc1 and > >> > he also bisected this to commit 61f5d698 "mm: re-enable THP". Further > >> > review of the THP rework patches, which cannot be bisected, revealed > >> > commit fecffad "s390, thp: remove infrastructure for handling splitting PMDs" > >> > (and also similar commits for other archs). > >> > > >> > This commit removes the THP splitting bit and also the architecture > >> > implementation of pmdp_splitting_flush(), which took care of the IPI for > >> > fast_gup serialization. The commit message says > >> > > >> > pmdp_splitting_flush() is not needed too: on splitting PMD we will do > >> > pmdp_clear_flush() + set_pte_at(). pmdp_clear_flush() will do IPI as > >> > needed for fast_gup > >> > > >> > The assumption that a TLB flush will also produce an IPI is wrong on s390, > >> > and maybe also on other architectures, and I thought that this was actually > >> > the main reason for having an arch-specific pmdp_splitting_flush(). > >> > > >> > At least PowerPC and ARM also had an individual implementation of > >> > pmdp_splitting_flush() that used kick_all_cpus_sync() instead of a TLB > >> > flush to send the IPI, and those were also removed. Putting the arch > >> > maintainers and mailing lists on cc to verify. > >> > > >> > On s390 this will break the IPI serialization against fast_gup, which > >> > would certainly explain the random kernel crashes, please revert or fix > >> > the pmdp_splitting_flush() removal. > >> > >> Sorry for that. > >> > >> I believe, the problem was already addressed for PowerPC: > >> > >> http://lkml.kernel.org/g/454980831-16631-1-git-send-email-aneesh.kumar@linux.vnet.ibm.com > >> > >> I think kick_all_cpus_sync() in arch-specific pmdp_invalidate() would do > >> the trick, right? > > > > Hmm, not sure about that. After pmdp_invalidate(), a pmd_none() check in > > fast_gup will still return false, because the pmd is not empty (at least > > on s390). > > Why can't we do this ? I did this for ppc64. > > void pmdp_invalidate(struct vm_area_struct *vma, unsigned long address, > pmd_t *pmdp) > { > - pmd_hugepage_update(vma->vm_mm, address, pmdp, _PAGE_PRESENT, 0); > + pmd_hugepage_update(vma->vm_mm, address, pmdp, ~0UL, 0); > Wouldn't that semantically change what pmdp_invalidate() was supposed to do? The comment before the call says "the pmd_trans_huge and pmd_trans_splitting must remain set at all times on the pmd". So, after removing pmd_trans_splitting, it seems to be necessary to at least keep pmd_trans_huge set. In your case, the pmd would be completely cleared, which may help to find it in fast_gup with pmd_none(), but I'm not sure if this would open up other problems, e.g. with concurrent page faults. But I must also admit that my THP overview got a little rusty. > >So I don't see spontaneously how it will help fast_gup to break > > out to the slow path in case of THP splitting. > > > >> > >> If yes, I'll prepare patch tomorrow (some sleep required). > >> > > > > We'll check if adding kick_all_cpus_sync() to pmdp_invalidate() helps. > > It would also be good if Martin has a look at this, he'll return on > > Monday. > > -aneesh > > -- > To unsubscribe from this list: send the line "unsubscribe linux-s390" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org From mboxrd@z Thu Jan 1 00:00:00 1970 From: gerald.schaefer@de.ibm.com (Gerald Schaefer) Date: Fri, 12 Feb 2016 12:59:43 +0100 Subject: [BUG] random kernel crashes after THP rework on s390 (maybe also on PowerPC and ARM) In-Reply-To: <87a8n6shf2.fsf@linux.vnet.ibm.com> References: <20160211192223.4b517057@thinkpad> <20160211190942.GA10244@node.shutemov.name> <20160211205702.24f0d17a@thinkpad> <87a8n6shf2.fsf@linux.vnet.ibm.com> Message-ID: <20160212125943.1eb2ca9d@thinkpad> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Fri, 12 Feb 2016 09:34:33 +0530 "Aneesh Kumar K.V" wrote: > Gerald Schaefer writes: > > > On Thu, 11 Feb 2016 21:09:42 +0200 > > "Kirill A. Shutemov" wrote: > > > >> On Thu, Feb 11, 2016 at 07:22:23PM +0100, Gerald Schaefer wrote: > >> > Hi, > >> > > >> > Sebastian Ott reported random kernel crashes beginning with v4.5-rc1 and > >> > he also bisected this to commit 61f5d698 "mm: re-enable THP". Further > >> > review of the THP rework patches, which cannot be bisected, revealed > >> > commit fecffad "s390, thp: remove infrastructure for handling splitting PMDs" > >> > (and also similar commits for other archs). > >> > > >> > This commit removes the THP splitting bit and also the architecture > >> > implementation of pmdp_splitting_flush(), which took care of the IPI for > >> > fast_gup serialization. The commit message says > >> > > >> > pmdp_splitting_flush() is not needed too: on splitting PMD we will do > >> > pmdp_clear_flush() + set_pte_at(). pmdp_clear_flush() will do IPI as > >> > needed for fast_gup > >> > > >> > The assumption that a TLB flush will also produce an IPI is wrong on s390, > >> > and maybe also on other architectures, and I thought that this was actually > >> > the main reason for having an arch-specific pmdp_splitting_flush(). > >> > > >> > At least PowerPC and ARM also had an individual implementation of > >> > pmdp_splitting_flush() that used kick_all_cpus_sync() instead of a TLB > >> > flush to send the IPI, and those were also removed. Putting the arch > >> > maintainers and mailing lists on cc to verify. > >> > > >> > On s390 this will break the IPI serialization against fast_gup, which > >> > would certainly explain the random kernel crashes, please revert or fix > >> > the pmdp_splitting_flush() removal. > >> > >> Sorry for that. > >> > >> I believe, the problem was already addressed for PowerPC: > >> > >> http://lkml.kernel.org/g/454980831-16631-1-git-send-email-aneesh.kumar at linux.vnet.ibm.com > >> > >> I think kick_all_cpus_sync() in arch-specific pmdp_invalidate() would do > >> the trick, right? > > > > Hmm, not sure about that. After pmdp_invalidate(), a pmd_none() check in > > fast_gup will still return false, because the pmd is not empty (at least > > on s390). > > Why can't we do this ? I did this for ppc64. > > void pmdp_invalidate(struct vm_area_struct *vma, unsigned long address, > pmd_t *pmdp) > { > - pmd_hugepage_update(vma->vm_mm, address, pmdp, _PAGE_PRESENT, 0); > + pmd_hugepage_update(vma->vm_mm, address, pmdp, ~0UL, 0); > Wouldn't that semantically change what pmdp_invalidate() was supposed to do? The comment before the call says "the pmd_trans_huge and pmd_trans_splitting must remain set at all times on the pmd". So, after removing pmd_trans_splitting, it seems to be necessary to at least keep pmd_trans_huge set. In your case, the pmd would be completely cleared, which may help to find it in fast_gup with pmd_none(), but I'm not sure if this would open up other problems, e.g. with concurrent page faults. But I must also admit that my THP overview got a little rusty. > >So I don't see spontaneously how it will help fast_gup to break > > out to the slow path in case of THP splitting. > > > >> > >> If yes, I'll prepare patch tomorrow (some sleep required). > >> > > > > We'll check if adding kick_all_cpus_sync() to pmdp_invalidate() helps. > > It would also be good if Martin has a look at this, he'll return on > > Monday. > > -aneesh > > -- > To unsubscribe from this list: send the line "unsubscribe linux-s390" in > the body of a message to majordomo at vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html >