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 3F1B8C433EF for ; Wed, 24 Nov 2021 23:59:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S245174AbhKYACX (ORCPT ); Wed, 24 Nov 2021 19:02:23 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:37932 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237577AbhKYACV (ORCPT ); Wed, 24 Nov 2021 19:02:21 -0500 Received: from mail-qt1-x849.google.com (mail-qt1-x849.google.com [IPv6:2607:f8b0:4864:20::849]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 2E2AFC061574 for ; Wed, 24 Nov 2021 15:59:11 -0800 (PST) Received: by mail-qt1-x849.google.com with SMTP id v32-20020a05622a18a000b002b04d0d410dso3941526qtc.11 for ; Wed, 24 Nov 2021 15:59:11 -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=gkTIFHzn7lWgA+OKJcWBkA+tgUB9Kv7MlnOSivNnZuA=; b=XZom6cLEXCTPPg13cihmjgx6jWLpE3yE6iuM/1xq7DRR8mxgE5ul9FDawNKWZp34V6 6QX4exQioKgzqwnbZ0RQ1BN1+kX+fygi+9BTQPyFQMYvOqLH6qg/352p4Tq+6VCOf2j7 Bz+S9nuwfpMre1gMME6RfyuQFS5rqfyB44luHdfqiVVMYMhcYi/WjdkyzQApNr4TJB/S /k1JCx3aKgUVTuJYSQhFnqJX05+yUyHrYy0m2M4C1sealksJQCec7ivd6C0eBxWfnCKT CjVMHKLvn5KEaLJ9p5fZXwIgCtGAzUGGoFDBXnXor72VgMagnD2HupmJhaGIvJIpESQP 358Q== 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=gkTIFHzn7lWgA+OKJcWBkA+tgUB9Kv7MlnOSivNnZuA=; b=shHdJJ61Jwdsa8vkYqxnbzuSHQePwqm7/eOMzMV+0pWMwurnSim4DUSVyYdmWahj8i UHjZtEPvIqs8FftuZ+ztMnCAElkjtvjq6kQyxqSAdh+a0RYSlmjOd5qeKl9eqmDqX9nP yj6aLAHnKAoKpin8EkqR1PcY2zEnWJl4pjIfWkHpjXvet8dJCTH9Qhf2Ipx6zjFeoUq1 2/KQisK98tg6F3o1KAFYuEteHYWlgea9VbWG4OsdhA7wUBYOv+PflKePGQis5at93bIg IZ8lqYTeKiqgJRQbgEbM2jvzRSQbrgEfUZF1mxPild3sw/1OZ8CiGv6sh0cgmMn+9g7o zLHw== X-Gm-Message-State: AOAM532C6ii7mWI7dhPC1yBUQaIxtAp39/ddexKa3EJh6+MI80DkRvdw 3mFKOa13XYRnpOwoYBFZC7xAAV+FUyc= X-Google-Smtp-Source: ABdhPJyCFoO8iT7UKnJAGhIvllYLx1WxReppQlKxurAYcQqseTCbk016W9Tt2SXNW0ZaJC2hr6A+WzzKMS8= X-Received: from surenb-desktop.mtv.corp.google.com ([2620:15c:211:200:e6ae:ce8f:3b61:8f18]) (user=surenb job=sendgmr) by 2002:ac8:4e51:: with SMTP id e17mr12207103qtw.129.1637798349867; Wed, 24 Nov 2021 15:59:09 -0800 (PST) Date: Wed, 24 Nov 2021 15:59:05 -0800 Message-Id: <20211124235906.14437-1-surenb@google.com> Mime-Version: 1.0 X-Mailer: git-send-email 2.34.0.rc2.393.gf8c9666880-goog Subject: [PATCH v2 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 --- changes in v2 - Moved mmap_write_unlock to cover remove_vma loop as well, per Matthew Wilcox mm/mmap.c | 16 ++++++++-------- 1 file changed, 8 insertions(+), 8 deletions(-) diff --git a/mm/mmap.c b/mm/mmap.c index bfb0ea164a90..f4e09d390a07 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); @@ -3171,16 +3173,14 @@ void exit_mmap(struct mm_struct *mm) free_pgtables(&tlb, vma, FIRST_USER_ADDRESS, USER_PGTABLES_CEILING); tlb_finish_mmu(&tlb); - /* - * Walk the list again, actually closing and freeing it, - * with preemption enabled, without holding any MM locks. - */ + /* Walk the list again, actually closing and freeing it. */ while (vma) { if (vma->vm_flags & VM_ACCOUNT) nr_accounted += vma_pages(vma); vma = remove_vma(vma); cond_resched(); } + mmap_write_unlock(mm); vm_unacct_memory(nr_accounted); } -- 2.34.0.rc2.393.gf8c9666880-goog