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 X-Spam-Level: X-Spam-Status: No, score=-26.3 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_GIT,USER_IN_DEF_DKIM_WL autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 78FE6C433ED for ; Thu, 1 Apr 2021 19:21:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5189C61001 for ; Thu, 1 Apr 2021 19:21:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235050AbhDATVh (ORCPT ); Thu, 1 Apr 2021 15:21:37 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51148 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234160AbhDATVK (ORCPT ); Thu, 1 Apr 2021 15:21:10 -0400 Received: from mail-qk1-x749.google.com (mail-qk1-x749.google.com [IPv6:2607:f8b0:4864:20::749]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 56D2FC048F2E for ; Thu, 1 Apr 2021 11:17:54 -0700 (PDT) Received: by mail-qk1-x749.google.com with SMTP id p133so4273936qka.17 for ; Thu, 01 Apr 2021 11:17:54 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=date:in-reply-to:message-id:mime-version:references:subject:from:to :cc; bh=xxiAXSo3VjIRKYILlCaYgYwnfwMxsag7xg8F7C8V4gk=; b=WHCnyfgYE72BsxoC3+we8HzNs4Cc2W1zdmE2FBIe8p+ZzPpPzsPi4TtDXqwNyNCWiP +Gg6WechHI5zDExRJ9YvYIIXygcLqALrlFi3u3gY01HPKlZgpBcGUJUK1CmSam6/Gtpb z1zC77H9PxKT39XC6llEq3qNKJTrdeTO/C1UAuUipIPijkof5was8wfysttuQOB6Ul9K p5zoGxqTEtpRm/rRTG8FoFoUO60ZHTf9Ho6P8g4rHxBaF9VnMrRhVQ0REouKLdZYLUO7 9MQ5wPt6Sejmp+5AnwsHVoj0KjgBeostzPsWDXVe2OmFvRkatC4LvBzmvvzybLQTKqvP yE5w== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:in-reply-to:message-id:mime-version :references:subject:from:to:cc; bh=xxiAXSo3VjIRKYILlCaYgYwnfwMxsag7xg8F7C8V4gk=; b=AliaQa+p/dk1V7kHGpl0B6M/bXS8ENRCSrjeQu6Ogdk/lxXsoLLQroB7df3NWd/DQS p6pq31LSy+wBR6YQwxu9bGVtQEa6HS5AgvvCVEjNjgqkiKVnyXMuAWguf9N/UWDozyPN xG9tgui/Sbg4mYgoS/BWK8nqwsTeXZ584UfN9r+H/qTJtN11c08S5zMZ5/y6GPlxfwNW XCEaCg/TI8vuaz1yQRXP0S8rStmxk8ALvj8e0aMPfA0a8QRHpN1LkE38P8aP5gifxJXC penVWeUjJ7PVDvv5gGeX3/0Ng4DbVPyluRPxq/kriyG4kgZGXm9uC2i9dNCks1mBs80C 3pkQ== X-Gm-Message-State: AOAM530Tve52t0fbfx/CD2eDWKtqgxyaeZluGMMEVc6ifuv12BqVgn1H V26ZKMA0ffM6IiT1/bSAMsYWZpNJn6g= X-Google-Smtp-Source: ABdhPJzWpshHJYnTRPhKzhXMsIiS2RDdrBVS8l2L80P/crekRlC8oE3WyRSgXrn5+ygoLXbaAAC9XSW3rIs= X-Received: from surenb1.mtv.corp.google.com ([2620:15c:211:200:899:1066:21fc:b3c5]) (user=surenb job=sendgmr) by 2002:a05:6214:9c9:: with SMTP id dp9mr9503117qvb.34.1617301073524; Thu, 01 Apr 2021 11:17:53 -0700 (PDT) Date: Thu, 1 Apr 2021 11:17:39 -0700 In-Reply-To: <20210401181741.168763-1-surenb@google.com> Message-Id: <20210401181741.168763-4-surenb@google.com> Mime-Version: 1.0 References: <20210401181741.168763-1-surenb@google.com> X-Mailer: git-send-email 2.31.0.291.g576ba9dcdaf-goog Subject: [PATCH 3/5] mm: fix misplaced unlock_page in do_wp_page() From: Suren Baghdasaryan To: stable@vger.kernel.org Cc: gregkh@linuxfoundation.org, jannh@google.com, ktkhai@virtuozzo.com, torvalds@linux-foundation.org, shli@fb.com, namit@vmware.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@android.com, Qian Cai , Alex Shi , Gerald Schaefer Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Linus Torvalds Commit 09854ba94c6a ("mm: do_wp_page() simplification") reorganized all the code around the page re-use vs copy, but in the process also moved the final unlock_page() around to after the wp_page_reuse() call. That normally doesn't matter - but it means that the unlock_page() is now done after releasing the page table lock. Again, not a big deal, you'd think. But it turns out that it's very wrong indeed, because once we've released the page table lock, we've basically lost our only reference to the page - the page tables - and it could now be free'd at any time. We do hold the mmap_sem, so no actual unmap() can happen, but madvise can come in and a MADV_DONTNEED will zap the page range - and free the page. So now the page may be free'd just as we're unlocking it, which in turn will usually trigger a "Bad page state" error in the freeing path. To make matters more confusing, by the time the debug code prints out the page state, the unlock has typically completed and everything looks fine again. This all doesn't happen in any normal situations, but it does trigger with the dirtyc0w_child LTP test. And it seems to trigger much more easily (but not expclusively) on s390 than elsewhere, probably because s390 doesn't do the "batch pages up for freeing after the TLB flush" that gives the unlock_page() more time to complete and makes the race harder to hit. Fixes: 09854ba94c6a ("mm: do_wp_page() simplification") Link: https://lore.kernel.org/lkml/a46e9bbef2ed4e17778f5615e818526ef848d791.camel@redhat.com/ Link: https://lore.kernel.org/linux-mm/c41149a8-211e-390b-af1d-d5eee690fecb@linux.alibaba.com/ Reported-by: Qian Cai Reported-by: Alex Shi Bisected-and-analyzed-by: Gerald Schaefer Tested-by: Gerald Schaefer Signed-off-by: Linus Torvalds --- mm/memory.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/mm/memory.c b/mm/memory.c index e84648d81d6d..14470ceaf3f2 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -2848,8 +2848,8 @@ static int do_wp_page(struct vm_fault *vmf) * page count reference, and the page is locked, * it's dark out, and we're wearing sunglasses. Hit it. */ - wp_page_reuse(vmf); unlock_page(page); + wp_page_reuse(vmf); return VM_FAULT_WRITE; } else if (unlikely((vma->vm_flags & (VM_WRITE|VM_SHARED)) == (VM_WRITE|VM_SHARED))) { -- 2.31.0.291.g576ba9dcdaf-goog