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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9A4D1C433F5 for ; Tue, 16 Nov 2021 21:57:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 768D063223 for ; Tue, 16 Nov 2021 21:57:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231639AbhKPWAS (ORCPT ); Tue, 16 Nov 2021 17:00:18 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58498 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229593AbhKPWAS (ORCPT ); Tue, 16 Nov 2021 17:00:18 -0500 Received: from mail-pg1-x549.google.com (mail-pg1-x549.google.com [IPv6:2607:f8b0:4864:20::549]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 943C2C061570 for ; Tue, 16 Nov 2021 13:57:20 -0800 (PST) Received: by mail-pg1-x549.google.com with SMTP id y18-20020a634952000000b002ecc060ccc8so193363pgk.17 for ; Tue, 16 Nov 2021 13:57:20 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=date:message-id:mime-version:subject:from:to:cc; bh=Ds7CkJIXOL2mYL105KfyaplaQRNJT0sgaXWilVjc75w=; b=a4UUleXv4Vh0+4iNT2NyvFFpMROT9+yq0O/b+cpkv7VQa6AYLh4gfJfXpvxTfZbEH5 OPQn3NsKK79KyNEWT2Wyz0IRL/kOkJRIKvprEB5pu8jdfHXz5d4Ba01tNMMqIyuSUTFZ xMQ1rqK2GQX0Kfqv7ATKT7TGPs3AkOcHPbNOPAthwrZFdqKRyCEohjAgfvyYXOPgnnGg YWwhwcvY2C4XBGMJvrDfZlq1ILMglQO+sB6sDRhWjDM3gOQNbZNPteXwHqo4/CaHHPnY xjsMVcjn79zbjBbMC32Qakfoof0Dwlv7rchpJzMujCNyk8bq3ZXweo/rWiKDwWg44E1R BzVQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:message-id:mime-version:subject:from:to:cc; bh=Ds7CkJIXOL2mYL105KfyaplaQRNJT0sgaXWilVjc75w=; b=fIAx5BNmmEYCeCQ9mQut9Qi1TebxTlsNGgx3ad/Lql0QI9TmMtfLpz+iHGNors0hLb tEFYlWaJ4izE9FvZakAOEX00W3CNEZa3K6wDPyUk/cg37yjXjvclYB7FpLCJJ5FnZJAD BnTpKJl+wn84gwPC9uJ/B8rdUtE0YnuxQzVccZmYHoRrPwFOHphJ7SKXX6EFDqd0REgb SsMnP32FkrCw8xe8dxux+KCPfOHWj1bJk5yf4ufvXFSbYe2H9J9Op0AS5BImBUQskXtt PjQNbH3hLJaLaoNfn0JN2nr7we+QuSYddu/U/oEo2g2skeExqQTCgPvdobee9myi1tae 4XQA== X-Gm-Message-State: AOAM532pXRLIN9KNRkBeR2wo9vJPp9664gv/5oo1FMcOEN1qJ9r7njfH w5ew2Bz4a3Ddsr1vclekWVSAkiREyU8= X-Google-Smtp-Source: ABdhPJye+XfttuNAxgGm4XDnZjHBwsdwvyOlKQAeoGZWLGAuc/JE6AaUFQlJvGYlhrKfh4nhYdVuXmyX5pE= X-Received: from surenb-desktop.mtv.corp.google.com ([2620:15c:211:200:91d1:d198:1088:5801]) (user=surenb job=sendgmr) by 2002:a17:902:b718:b0:143:72b7:409e with SMTP id d24-20020a170902b71800b0014372b7409emr48831424pls.28.1637099839672; Tue, 16 Nov 2021 13:57:19 -0800 (PST) Date: Tue, 16 Nov 2021 13:57:14 -0800 Message-Id: <20211116215715.645231-1-surenb@google.com> Mime-Version: 1.0 X-Mailer: git-send-email 2.34.0.rc2.393.gf8c9666880-goog Subject: [PATCH 1/2] mm: protect free_pgtables with mmap_lock write lock in exit_mmap From: Suren Baghdasaryan To: akpm@linux-foundation.org Cc: mhocko@kernel.org, mhocko@suse.com, rientjes@google.com, willy@infradead.org, hannes@cmpxchg.org, guro@fb.com, riel@surriel.com, minchan@kernel.org, kirill@shutemov.name, aarcange@redhat.com, christian@brauner.io, hch@infradead.org, oleg@redhat.com, david@redhat.com, jannh@google.com, shakeelb@google.com, luto@kernel.org, christian.brauner@ubuntu.com, fweimer@redhat.com, jengelh@inai.de, timmurray@google.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@android.com, surenb@google.com Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org oom-reaper and process_mrelease system call should protect against races with exit_mmap which can destroy page tables while they walk the VMA tree. oom-reaper protects from that race by setting MMF_OOM_VICTIM and by relying on exit_mmap to set MMF_OOM_SKIP before taking and releasing mmap_write_lock. process_mrelease has to elevate mm->mm_users to prevent such race. Both oom-reaper and process_mrelease hold mmap_read_lock when walking the VMA tree. The locking rules and mechanisms could be simpler if exit_mmap takes mmap_write_lock while executing destructive operations such as free_pgtables. Change exit_mmap to hold the mmap_write_lock when calling free_pgtables. Operations like unmap_vmas() and unlock_range() are not destructive and could run under mmap_read_lock but for simplicity we take one mmap_write_lock during almost the entire operation. Note also that because oom-reaper checks VM_LOCKED flag, unlock_range() should not be allowed to race with it. In most cases this lock should be uncontended. Previously, Kirill reported ~4% regression caused by a similar change [1]. We reran the same test and although the individual results are quite noisy, the percentiles show lower regression with 1.6% being the worst case [2]. The change allows oom-reaper and process_mrelease to execute safely under mmap_read_lock without worries that exit_mmap might destroy page tables from under them. [1] https://lore.kernel.org/all/20170725141723.ivukwhddk2voyhuc@node.shutemov.name/ [2] https://lore.kernel.org/all/CAJuCfpGC9-c9P40x7oy=jy5SphMcd0o0G_6U1-+JAziGKG6dGA@mail.gmail.com/ Signed-off-by: Suren Baghdasaryan --- mm/mmap.c | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-) diff --git a/mm/mmap.c b/mm/mmap.c index bfb0ea164a90..69b3036c6dee 100644 --- a/mm/mmap.c +++ b/mm/mmap.c @@ -3142,25 +3142,27 @@ void exit_mmap(struct mm_struct *mm) * to mmu_notifier_release(mm) ensures mmu notifier callbacks in * __oom_reap_task_mm() will not block. * - * This needs to be done before calling munlock_vma_pages_all(), + * This needs to be done before calling unlock_range(), * which clears VM_LOCKED, otherwise the oom reaper cannot * reliably test it. */ (void)__oom_reap_task_mm(mm); set_bit(MMF_OOM_SKIP, &mm->flags); - mmap_write_lock(mm); - mmap_write_unlock(mm); } + mmap_write_lock(mm); if (mm->locked_vm) unlock_range(mm->mmap, ULONG_MAX); arch_exit_mmap(mm); vma = mm->mmap; - if (!vma) /* Can happen if dup_mmap() received an OOM */ + if (!vma) { + /* Can happen if dup_mmap() received an OOM */ + mmap_write_unlock(mm); return; + } lru_add_drain(); flush_cache_mm(mm); @@ -3170,6 +3172,7 @@ void exit_mmap(struct mm_struct *mm) unmap_vmas(&tlb, vma, 0, -1); free_pgtables(&tlb, vma, FIRST_USER_ADDRESS, USER_PGTABLES_CEILING); tlb_finish_mmu(&tlb); + mmap_write_unlock(mm); /* * Walk the list again, actually closing and freeing it, -- 2.34.0.rc1.387.gb447b232ab-goog