From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id A804BC433EF for ; Tue, 15 Mar 2022 19:07:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1350363AbiCOTJF (ORCPT ); Tue, 15 Mar 2022 15:09:05 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38862 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S245487AbiCOTJC (ORCPT ); Tue, 15 Mar 2022 15:09:02 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 79EAADA9 for ; Tue, 15 Mar 2022 12:07:47 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1647371267; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=fBJf1R7kBM9gH+xhtNa/kOhtVdAYjEafv1mIR3CkHEI=; b=a02ENoeAkU4H1SxZNuyf7cP0Rqd3nz3Nz1EWmF8nCz3aleTwmNLpN8V2YdlMaWeXn7zqb/ A+Fc/A+yBoU8P3SS1WOTK41LK2/DV6UzTa54p4+RnqhSaU7pb3sJLj8WOShX+vwKqLIT1K LUn3wX3zqZNeIx/LMJT0O7tKsKjvKfI= Received: from mail-wr1-f69.google.com (mail-wr1-f69.google.com [209.85.221.69]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-488-Y4HYs6etMH-c-cgy4F4Y0w-1; Tue, 15 Mar 2022 15:07:46 -0400 X-MC-Unique: Y4HYs6etMH-c-cgy4F4Y0w-1 Received: by mail-wr1-f69.google.com with SMTP id a16-20020adff7d0000000b001f0473a6b25so5646306wrq.1 for ; Tue, 15 Mar 2022 12:07:45 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:message-id:date:mime-version:user-agent:subject :content-language:to:cc:references:from:organization:in-reply-to :content-transfer-encoding; bh=fBJf1R7kBM9gH+xhtNa/kOhtVdAYjEafv1mIR3CkHEI=; b=Qbq1waiA93gl6cJsaw0lbcexMShxYMwf5vcK3B5zjfYJI6p6+ziT7BqeLrdCvjpFfy rhJWIdQyRlShlcfw2DR/3SLzppyFQX6zh2VnDZ9JsXDxN+OSpXk7/bLab9Opzw6ruYjT dgzqa4XS438VVrKiyRtZAMoleUmhJ0QImEfJmnFS88W+58jwGPaMmSFAcU15tsJaTW73 y1PsGTB8bkr/wFgS0Q1uBKkj5E0MRUcABk+HY+GUQt7e/q4ezDZ2aIQ1biJZpou+Gxuk MIE/X7G/aQZp4RIiNVVW/SrUNX8eQc6hmKfx/vFE8WJ+6V8PrbkoSJQrE4JgHI7GzRuP bNzw== X-Gm-Message-State: AOAM531yzbY21jWDgSbnao4O/AXxjynR/0Ebg3rwEhOFUqsz3LIH06dQ LWdVANBLSAl+ZGw/kzRgmIaueMWu6G3KuWknDxrXYmFmtWjxTajoYyjR4ZXMM6LDzkK7kpv4M5Z jhT+QwozVco8+ha4b0I2cNGgK X-Received: by 2002:a05:600c:1c9f:b0:389:cf43:da64 with SMTP id k31-20020a05600c1c9f00b00389cf43da64mr4480395wms.206.1647371264797; Tue, 15 Mar 2022 12:07:44 -0700 (PDT) X-Google-Smtp-Source: ABdhPJxyzLlJbwR1xveI8URJ60kP+00Vz8I0FYYiVHPL3IeEWq8UXFCK8AWIjfhzlGgS3nbkP0cs5A== X-Received: by 2002:a05:600c:1c9f:b0:389:cf43:da64 with SMTP id k31-20020a05600c1c9f00b00389cf43da64mr4480382wms.206.1647371264585; Tue, 15 Mar 2022 12:07:44 -0700 (PDT) Received: from ?IPV6:2003:cb:c708:1800:42bd:3cac:d22a:3c62? (p200300cbc708180042bd3cacd22a3c62.dip0.t-ipconnect.de. [2003:cb:c708:1800:42bd:3cac:d22a:3c62]) by smtp.gmail.com with ESMTPSA id b15-20020adfc74f000000b001e888b871a0sm16915200wrh.87.2022.03.15.12.07.43 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 15 Mar 2022 12:07:43 -0700 (PDT) Message-ID: Date: Tue, 15 Mar 2022 20:07:42 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.6.2 Subject: Re: [PATCH] mm/migrate: fix race between lock page and clear PG_Isolated Content-Language: en-US To: Matthew Wilcox Cc: Andrew Morton , Andrew Yang , Matthias Brugger , Vlastimil Babka , David Howells , William Kucharski , Yang Shi , Marc Zyngier , linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, linux-mediatek@lists.infradead.org, wsd_upstream@mediatek.com, Nicholas Tang , Kuan-Ying Lee References: <20220315030515.20263-1-andrew.yang@mediatek.com> <20220314212127.a2797926ee0ef8a7ad05dcaa@linux-foundation.org> <4cb789a5-c49c-f095-1f7e-67be65ba508a@redhat.com> From: David Hildenbrand Organization: Red Hat In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 15.03.22 18:43, Matthew Wilcox wrote: > On Tue, Mar 15, 2022 at 04:45:13PM +0100, David Hildenbrand wrote: >> On 15.03.22 05:21, Andrew Morton wrote: >>> On Tue, 15 Mar 2022 11:05:15 +0800 Andrew Yang wrote: >>> >>>> When memory is tight, system may start to compact memory for large >>>> continuous memory demands. If one process tries to lock a memory page >>>> that is being locked and isolated for compaction, it may wait a long time >>>> or even forever. This is because compaction will perform non-atomic >>>> PG_Isolated clear while holding page lock, this may overwrite PG_waiters >>>> set by the process that can't obtain the page lock and add itself to the >>>> waiting queue to wait for the lock to be unlocked. >>>> >>>> CPU1 CPU2 >>>> lock_page(page); (successful) >>>> lock_page(); (failed) >>>> __ClearPageIsolated(page); SetPageWaiters(page) (may be overwritten) >>>> unlock_page(page); >>>> >>>> The solution is to not perform non-atomic operation on page flags while >>>> holding page lock. >>> >>> Sure, the non-atomic bitop optimization is really risky and I suspect >>> we reach for it too often. Or at least without really clearly >>> demonstrating that it is safe, and documenting our assumptions. >> >> I agree. IIRC, non-atomic variants are mostly only safe while the >> refcount is 0. Everything else is just absolutely fragile. > > We could add an assertion ... I just tried this: > > +++ b/include/linux/page-flags.h > @@ -342,14 +342,16 @@ static __always_inline \ > void __folio_set_##lname(struct folio *folio) \ > { __set_bit(PG_##lname, folio_flags(folio, FOLIO_##policy)); } \ > static __always_inline void __SetPage##uname(struct page *page) \ > -{ __set_bit(PG_##lname, &policy(page, 1)->flags); } > +{ VM_BUG_ON_PGFLAGS(atomic_read(&policy(page, 1)->_refcount), page); \ > + __set_bit(PG_##lname, &policy(page, 1)->flags); } > > #define __CLEARPAGEFLAG(uname, lname, policy) \ > static __always_inline \ > void __folio_clear_##lname(struct folio *folio) \ > { __clear_bit(PG_##lname, folio_flags(folio, FOLIO_##policy)); } \ > static __always_inline void __ClearPage##uname(struct page *page) \ > -{ __clear_bit(PG_##lname, &policy(page, 1)->flags); } > +{ VM_BUG_ON_PGFLAGS(atomic_read(&policy(page, 1)->_refcount), page); \ > + __clear_bit(PG_##lname, &policy(page, 1)->flags); } > > #define TESTSETFLAG(uname, lname, policy) \ > static __always_inline \ > > ... but it dies _really_ early: > > (gdb) bt > #0 0xffffffff820055e5 in native_halt () > at ../arch/x86/include/asm/irqflags.h:57 > #1 halt () at ../arch/x86/include/asm/irqflags.h:98 > #2 early_fixup_exception (regs=regs@entry=0xffffffff81e03cf8, > trapnr=trapnr@entry=6) at ../arch/x86/mm/extable.c:283 > #3 0xffffffff81ff243c in do_early_exception (regs=0xffffffff81e03cf8, > trapnr=6) at ../arch/x86/kernel/head64.c:419 > #4 0xffffffff81ff214f in early_idt_handler_common () > at ../arch/x86/kernel/head_64.S:417 > #5 0x0000000000000000 in ?? () > > and honestly, I'm not sure how to debug something that goes wrong this > early. Maybe I need to make that start warning 5 seconds after boot > or only if we're not in pid 1, or something ... Maybe checking for "system_state >= SYSTEM_RUNNING" or "system_state >= SYSTEM_SCHEDULING" to exclude early boot where no (real) concurrency is happening. But I assume you'll still get plenty of such reports. -- Thanks, David / dhildenb From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 4DE61C433F5 for ; Tue, 15 Mar 2022 19:07:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:From:References:Cc:To: Subject:MIME-Version:Date:Message-ID:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=OD0rUBsFbNT3ZWOluNcq3ml5obnQ3hpz5bYGARgmcHk=; b=abEgedYV9mm8R8 MfNcjctr4zWgrbs1oEvTtQigLFyFHBacRnOn6vs2LG9v2YejOs8AfDHwqcF9BiDUPMWfWIe1YInVX J8iatdqtWYZ9/laejc6wSjieCCcK82i7v7Z1smQYoDqoVaS6CblbS74U+MxLRGhya4ljTFgYUzQqO Ttgxs4OPQz10RHOl9QxfQ4DGKBJfkAznwN+PUofahYcU8LdumXAreHusiJmfDgHMnlOEz3HzMgtIo dsoZ7gd8daNgKMbyzXQekj7rNjzxtfSU8mZjFky2zunSZYRFDg9AyjOter7SyhafrwsD3vYygCQ+L odwB1vowCMYiDICoD92Q==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1nUCWN-00APwq-Fm; Tue, 15 Mar 2022 19:07:51 +0000 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1nUCWK-00APvJ-8d for linux-mediatek@lists.infradead.org; Tue, 15 Mar 2022 19:07:49 +0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1647371267; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=fBJf1R7kBM9gH+xhtNa/kOhtVdAYjEafv1mIR3CkHEI=; b=a02ENoeAkU4H1SxZNuyf7cP0Rqd3nz3Nz1EWmF8nCz3aleTwmNLpN8V2YdlMaWeXn7zqb/ A+Fc/A+yBoU8P3SS1WOTK41LK2/DV6UzTa54p4+RnqhSaU7pb3sJLj8WOShX+vwKqLIT1K LUn3wX3zqZNeIx/LMJT0O7tKsKjvKfI= Received: from mail-wr1-f70.google.com (mail-wr1-f70.google.com [209.85.221.70]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-115-jsMZnFLANkyKmM4SS9uxCA-1; Tue, 15 Mar 2022 15:07:45 -0400 X-MC-Unique: jsMZnFLANkyKmM4SS9uxCA-1 Received: by mail-wr1-f70.google.com with SMTP id f9-20020a5d58e9000000b001f0247e5e96so5635684wrd.15 for ; Tue, 15 Mar 2022 12:07:45 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:message-id:date:mime-version:user-agent:subject :content-language:to:cc:references:from:organization:in-reply-to :content-transfer-encoding; bh=fBJf1R7kBM9gH+xhtNa/kOhtVdAYjEafv1mIR3CkHEI=; b=qdTea0zQg20GbXzCswbENKk4VtHrCdKt3VE/ugJc4fnsUFTa+JZnDniRditu9ugR0g 20Y/NRZ7Y457X/HgsA3STYjY3BV9zAP0KvAvofIVccaNnV4xe45qWfAvFVPUIWEUnzIv OvIAiEUdWEdSgKlg9z8QLe5bt/VzWi3gwX5uht2sy205JQ/TjFy5JBsIQg3sAPHSVgLh EWAb50fC7Fx9l2SJr8AYhFOwSfX8h+p785cOoUV/77y1XZky2R+o4HO9siQvv5mG4qEt YS5yV3A/BliNazIBtdpugJqamPVw0tL8n7IPlz8UWZQ+shC5PHus1oiGjGseAdJcaARd xjbQ== X-Gm-Message-State: AOAM532ATqjToM94oo9tRqSujYiEQZ9E8msGRonjKMeYjBdK7p7617+8 nGw8jjhWmq9Q3CBgNmFPNh5c8D0fq8F4WsRFhj5E34BkJkvdNMcojpMQztF44MF5WPMObfxWr07 JdgjdWlH+R7+4bZnlc+4a8bOBOi6NMkgm X-Received: by 2002:a05:600c:1c9f:b0:389:cf43:da64 with SMTP id k31-20020a05600c1c9f00b00389cf43da64mr4480388wms.206.1647371264793; Tue, 15 Mar 2022 12:07:44 -0700 (PDT) X-Google-Smtp-Source: ABdhPJxyzLlJbwR1xveI8URJ60kP+00Vz8I0FYYiVHPL3IeEWq8UXFCK8AWIjfhzlGgS3nbkP0cs5A== X-Received: by 2002:a05:600c:1c9f:b0:389:cf43:da64 with SMTP id k31-20020a05600c1c9f00b00389cf43da64mr4480382wms.206.1647371264585; Tue, 15 Mar 2022 12:07:44 -0700 (PDT) Received: from ?IPV6:2003:cb:c708:1800:42bd:3cac:d22a:3c62? (p200300cbc708180042bd3cacd22a3c62.dip0.t-ipconnect.de. [2003:cb:c708:1800:42bd:3cac:d22a:3c62]) by smtp.gmail.com with ESMTPSA id b15-20020adfc74f000000b001e888b871a0sm16915200wrh.87.2022.03.15.12.07.43 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 15 Mar 2022 12:07:43 -0700 (PDT) Message-ID: Date: Tue, 15 Mar 2022 20:07:42 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.6.2 Subject: Re: [PATCH] mm/migrate: fix race between lock page and clear PG_Isolated To: Matthew Wilcox Cc: Andrew Morton , Andrew Yang , Matthias Brugger , Vlastimil Babka , David Howells , William Kucharski , Yang Shi , Marc Zyngier , linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, linux-mediatek@lists.infradead.org, wsd_upstream@mediatek.com, Nicholas Tang , Kuan-Ying Lee References: <20220315030515.20263-1-andrew.yang@mediatek.com> <20220314212127.a2797926ee0ef8a7ad05dcaa@linux-foundation.org> <4cb789a5-c49c-f095-1f7e-67be65ba508a@redhat.com> From: David Hildenbrand Organization: Red Hat In-Reply-To: Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=david@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20220315_120748_420767_E27870C0 X-CRM114-Status: GOOD ( 20.87 ) X-BeenThere: linux-mediatek@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "Linux-mediatek" Errors-To: linux-mediatek-bounces+linux-mediatek=archiver.kernel.org@lists.infradead.org On 15.03.22 18:43, Matthew Wilcox wrote: > On Tue, Mar 15, 2022 at 04:45:13PM +0100, David Hildenbrand wrote: >> On 15.03.22 05:21, Andrew Morton wrote: >>> On Tue, 15 Mar 2022 11:05:15 +0800 Andrew Yang wrote: >>> >>>> When memory is tight, system may start to compact memory for large >>>> continuous memory demands. If one process tries to lock a memory page >>>> that is being locked and isolated for compaction, it may wait a long time >>>> or even forever. This is because compaction will perform non-atomic >>>> PG_Isolated clear while holding page lock, this may overwrite PG_waiters >>>> set by the process that can't obtain the page lock and add itself to the >>>> waiting queue to wait for the lock to be unlocked. >>>> >>>> CPU1 CPU2 >>>> lock_page(page); (successful) >>>> lock_page(); (failed) >>>> __ClearPageIsolated(page); SetPageWaiters(page) (may be overwritten) >>>> unlock_page(page); >>>> >>>> The solution is to not perform non-atomic operation on page flags while >>>> holding page lock. >>> >>> Sure, the non-atomic bitop optimization is really risky and I suspect >>> we reach for it too often. Or at least without really clearly >>> demonstrating that it is safe, and documenting our assumptions. >> >> I agree. IIRC, non-atomic variants are mostly only safe while the >> refcount is 0. Everything else is just absolutely fragile. > > We could add an assertion ... I just tried this: > > +++ b/include/linux/page-flags.h > @@ -342,14 +342,16 @@ static __always_inline \ > void __folio_set_##lname(struct folio *folio) \ > { __set_bit(PG_##lname, folio_flags(folio, FOLIO_##policy)); } \ > static __always_inline void __SetPage##uname(struct page *page) \ > -{ __set_bit(PG_##lname, &policy(page, 1)->flags); } > +{ VM_BUG_ON_PGFLAGS(atomic_read(&policy(page, 1)->_refcount), page); \ > + __set_bit(PG_##lname, &policy(page, 1)->flags); } > > #define __CLEARPAGEFLAG(uname, lname, policy) \ > static __always_inline \ > void __folio_clear_##lname(struct folio *folio) \ > { __clear_bit(PG_##lname, folio_flags(folio, FOLIO_##policy)); } \ > static __always_inline void __ClearPage##uname(struct page *page) \ > -{ __clear_bit(PG_##lname, &policy(page, 1)->flags); } > +{ VM_BUG_ON_PGFLAGS(atomic_read(&policy(page, 1)->_refcount), page); \ > + __clear_bit(PG_##lname, &policy(page, 1)->flags); } > > #define TESTSETFLAG(uname, lname, policy) \ > static __always_inline \ > > ... but it dies _really_ early: > > (gdb) bt > #0 0xffffffff820055e5 in native_halt () > at ../arch/x86/include/asm/irqflags.h:57 > #1 halt () at ../arch/x86/include/asm/irqflags.h:98 > #2 early_fixup_exception (regs=regs@entry=0xffffffff81e03cf8, > trapnr=trapnr@entry=6) at ../arch/x86/mm/extable.c:283 > #3 0xffffffff81ff243c in do_early_exception (regs=0xffffffff81e03cf8, > trapnr=6) at ../arch/x86/kernel/head64.c:419 > #4 0xffffffff81ff214f in early_idt_handler_common () > at ../arch/x86/kernel/head_64.S:417 > #5 0x0000000000000000 in ?? () > > and honestly, I'm not sure how to debug something that goes wrong this > early. Maybe I need to make that start warning 5 seconds after boot > or only if we're not in pid 1, or something ... Maybe checking for "system_state >= SYSTEM_RUNNING" or "system_state >= SYSTEM_SCHEDULING" to exclude early boot where no (real) concurrency is happening. But I assume you'll still get plenty of such reports. -- Thanks, David / dhildenb _______________________________________________ Linux-mediatek mailing list Linux-mediatek@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-mediatek From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 7F61FC433EF for ; Tue, 15 Mar 2022 19:09:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:From:References:Cc:To: Subject:MIME-Version:Date:Message-ID:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=mcHreFC6zMNKunbeYQNO0V8P/xDiUY46OtxQ3PIv5Ik=; b=bPrcksAQsvOnPx Me06iQ91OjvLGr6xwFdqJ4Kc2kewQuONWw5sBvD8Y9W7sdaULk0AMnY31uezD4kHyvDWw+Htm8flZ NJzum4ZfIiAJ4vI8CsL7/EMcmSHJWkAK3E9hFwzxe6rXjg67SCx+eOuGoXB9QuMICwtLMvlV42Lel vVpGQ6PCe1odRVqIEQcLapmNtkcnryijhzI6gUu6vqP75U/QoZTYXkk7hTVcT7zlS55IbOiWWso6+ jLca7uTEL+jMsX8t5BmlREvZTmeVjYZpSzek6caHazSQVb15MhOti6qOuNwqOH6ARj5ThrmYu4MlK k6g0Ik2alz5EltLXzPPg==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1nUCWO-00APx0-UX; Tue, 15 Mar 2022 19:07:53 +0000 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1nUCWL-00APvK-Gb for linux-arm-kernel@lists.infradead.org; Tue, 15 Mar 2022 19:07:51 +0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1647371267; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=fBJf1R7kBM9gH+xhtNa/kOhtVdAYjEafv1mIR3CkHEI=; b=a02ENoeAkU4H1SxZNuyf7cP0Rqd3nz3Nz1EWmF8nCz3aleTwmNLpN8V2YdlMaWeXn7zqb/ A+Fc/A+yBoU8P3SS1WOTK41LK2/DV6UzTa54p4+RnqhSaU7pb3sJLj8WOShX+vwKqLIT1K LUn3wX3zqZNeIx/LMJT0O7tKsKjvKfI= Received: from mail-wr1-f72.google.com (mail-wr1-f72.google.com [209.85.221.72]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-658-m0tFb-eVNgyLpqb85x_AVQ-1; Tue, 15 Mar 2022 15:07:46 -0400 X-MC-Unique: m0tFb-eVNgyLpqb85x_AVQ-1 Received: by mail-wr1-f72.google.com with SMTP id 71-20020adf82cd000000b00203dc43d216so281416wrc.22 for ; Tue, 15 Mar 2022 12:07:45 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:message-id:date:mime-version:user-agent:subject :content-language:to:cc:references:from:organization:in-reply-to :content-transfer-encoding; bh=fBJf1R7kBM9gH+xhtNa/kOhtVdAYjEafv1mIR3CkHEI=; b=PD544yRreBGUItUxVFzIFW6ivbu92WaIu9iuCh/G1MyFV36TfoGJ+hdladm/P1idmO g+YOw8eY5JI1movRp5haP3xV80PuyS6n4OowPkmIABf0Zt32ETIJD+AO5WGQLR59GhB3 m9bA8GRxWTicGx0IhD0MBk2Fr1xtVgZxiVa+MyTrjJx5U+HjSbJy95PFuSfoSnJBtJer ddL8KoL6RdR0AYdBKBuIxBeTM5MLr00PZlEswP8GZILo9wHYscz5IvNYEqBxPK9igqkB LUcFmTxfzISTkIUmGKZxIjwzsLv6wbEhkOxcOauCglQiH2/tKwXe5C3BkQoqXxaZKYZl jsag== X-Gm-Message-State: AOAM5338EfhsNwFWw44zSObePfFPV4V6vbqhtXj6Aooer3zIaneMdjSI HqMmNKE117rwNAIbd9YZUxJFLuPgr+ZFKYLLU8D/7hlyOeKKH1JkqmoOt7JCwQgNqQ2BxNHs5yY ecmCf01dhmXLmh+eRNtu7pHF55BoKOBufk4I= X-Received: by 2002:a05:600c:1c9f:b0:389:cf43:da64 with SMTP id k31-20020a05600c1c9f00b00389cf43da64mr4480396wms.206.1647371264797; Tue, 15 Mar 2022 12:07:44 -0700 (PDT) X-Google-Smtp-Source: ABdhPJxyzLlJbwR1xveI8URJ60kP+00Vz8I0FYYiVHPL3IeEWq8UXFCK8AWIjfhzlGgS3nbkP0cs5A== X-Received: by 2002:a05:600c:1c9f:b0:389:cf43:da64 with SMTP id k31-20020a05600c1c9f00b00389cf43da64mr4480382wms.206.1647371264585; Tue, 15 Mar 2022 12:07:44 -0700 (PDT) Received: from ?IPV6:2003:cb:c708:1800:42bd:3cac:d22a:3c62? (p200300cbc708180042bd3cacd22a3c62.dip0.t-ipconnect.de. [2003:cb:c708:1800:42bd:3cac:d22a:3c62]) by smtp.gmail.com with ESMTPSA id b15-20020adfc74f000000b001e888b871a0sm16915200wrh.87.2022.03.15.12.07.43 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 15 Mar 2022 12:07:43 -0700 (PDT) Message-ID: Date: Tue, 15 Mar 2022 20:07:42 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.6.2 Subject: Re: [PATCH] mm/migrate: fix race between lock page and clear PG_Isolated To: Matthew Wilcox Cc: Andrew Morton , Andrew Yang , Matthias Brugger , Vlastimil Babka , David Howells , William Kucharski , Yang Shi , Marc Zyngier , linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, linux-mediatek@lists.infradead.org, wsd_upstream@mediatek.com, Nicholas Tang , Kuan-Ying Lee References: <20220315030515.20263-1-andrew.yang@mediatek.com> <20220314212127.a2797926ee0ef8a7ad05dcaa@linux-foundation.org> <4cb789a5-c49c-f095-1f7e-67be65ba508a@redhat.com> From: David Hildenbrand Organization: Red Hat In-Reply-To: Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=david@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20220315_120749_646784_F4E98F34 X-CRM114-Status: GOOD ( 22.40 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 15.03.22 18:43, Matthew Wilcox wrote: > On Tue, Mar 15, 2022 at 04:45:13PM +0100, David Hildenbrand wrote: >> On 15.03.22 05:21, Andrew Morton wrote: >>> On Tue, 15 Mar 2022 11:05:15 +0800 Andrew Yang wrote: >>> >>>> When memory is tight, system may start to compact memory for large >>>> continuous memory demands. If one process tries to lock a memory page >>>> that is being locked and isolated for compaction, it may wait a long time >>>> or even forever. This is because compaction will perform non-atomic >>>> PG_Isolated clear while holding page lock, this may overwrite PG_waiters >>>> set by the process that can't obtain the page lock and add itself to the >>>> waiting queue to wait for the lock to be unlocked. >>>> >>>> CPU1 CPU2 >>>> lock_page(page); (successful) >>>> lock_page(); (failed) >>>> __ClearPageIsolated(page); SetPageWaiters(page) (may be overwritten) >>>> unlock_page(page); >>>> >>>> The solution is to not perform non-atomic operation on page flags while >>>> holding page lock. >>> >>> Sure, the non-atomic bitop optimization is really risky and I suspect >>> we reach for it too often. Or at least without really clearly >>> demonstrating that it is safe, and documenting our assumptions. >> >> I agree. IIRC, non-atomic variants are mostly only safe while the >> refcount is 0. Everything else is just absolutely fragile. > > We could add an assertion ... I just tried this: > > +++ b/include/linux/page-flags.h > @@ -342,14 +342,16 @@ static __always_inline \ > void __folio_set_##lname(struct folio *folio) \ > { __set_bit(PG_##lname, folio_flags(folio, FOLIO_##policy)); } \ > static __always_inline void __SetPage##uname(struct page *page) \ > -{ __set_bit(PG_##lname, &policy(page, 1)->flags); } > +{ VM_BUG_ON_PGFLAGS(atomic_read(&policy(page, 1)->_refcount), page); \ > + __set_bit(PG_##lname, &policy(page, 1)->flags); } > > #define __CLEARPAGEFLAG(uname, lname, policy) \ > static __always_inline \ > void __folio_clear_##lname(struct folio *folio) \ > { __clear_bit(PG_##lname, folio_flags(folio, FOLIO_##policy)); } \ > static __always_inline void __ClearPage##uname(struct page *page) \ > -{ __clear_bit(PG_##lname, &policy(page, 1)->flags); } > +{ VM_BUG_ON_PGFLAGS(atomic_read(&policy(page, 1)->_refcount), page); \ > + __clear_bit(PG_##lname, &policy(page, 1)->flags); } > > #define TESTSETFLAG(uname, lname, policy) \ > static __always_inline \ > > ... but it dies _really_ early: > > (gdb) bt > #0 0xffffffff820055e5 in native_halt () > at ../arch/x86/include/asm/irqflags.h:57 > #1 halt () at ../arch/x86/include/asm/irqflags.h:98 > #2 early_fixup_exception (regs=regs@entry=0xffffffff81e03cf8, > trapnr=trapnr@entry=6) at ../arch/x86/mm/extable.c:283 > #3 0xffffffff81ff243c in do_early_exception (regs=0xffffffff81e03cf8, > trapnr=6) at ../arch/x86/kernel/head64.c:419 > #4 0xffffffff81ff214f in early_idt_handler_common () > at ../arch/x86/kernel/head_64.S:417 > #5 0x0000000000000000 in ?? () > > and honestly, I'm not sure how to debug something that goes wrong this > early. Maybe I need to make that start warning 5 seconds after boot > or only if we're not in pid 1, or something ... Maybe checking for "system_state >= SYSTEM_RUNNING" or "system_state >= SYSTEM_SCHEDULING" to exclude early boot where no (real) concurrency is happening. But I assume you'll still get plenty of such reports. -- Thanks, David / dhildenb _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel