From patchwork Wed Nov 24 23:59:05 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Suren Baghdasaryan X-Patchwork-Id: 12638131 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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 289C6C433EF for ; Wed, 24 Nov 2021 23:59:37 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 8AFB06B007B; Wed, 24 Nov 2021 18:59:21 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 838C76B007D; Wed, 24 Nov 2021 18:59:21 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 6D8D36B007E; Wed, 24 Nov 2021 18:59:21 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0229.hostedemail.com [216.40.44.229]) by kanga.kvack.org (Postfix) with ESMTP id 5821A6B007B for ; 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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=erKSTXX+OszRkF02Jtd/0ZVx0n6o7ZDyN/lfmSQL6rZnlw80cgSJ6nTafCaRzw+pU/ BSl23m++JyTpjXKOXdulq2xBnC1LEDmNPbEo36jW+3zOuNjb56e1/VdKOduCM+B/H296 QxfhhFbiyECb0HlOlfaIwQAp9Pl0IjJSExKqBisK7X5+vBWIk/xFPj1hTPt/gIijGMkH dczg+o2fDNm7EqezUoNFx0i8KcONEv0x9LfHfePbOCP2WjQNT90IuTPwHn1obUzgaAB6 Ye/igDQOc2mAqtVywLIi6rtBBrjqOzyWG96g5swOIXC6uiYIfD2j90/7szGjQba1n3Ik 70eg== X-Gm-Message-State: AOAM530HKT0KFNru03Cp4hzn5jxFSyVMNpsv/jQ7Pu4Y9bimSE4tvvSp rromgODjts/dqC11QyCkwpJGFjMs40c= 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 X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 75086D0369FE X-Stat-Signature: cbd9im7mzbmgfssr46b41ociom5mpuz9 Authentication-Results: imf21.hostedemail.com; dkim=pass header.d=google.com header.s=20210112 header.b=XZom6cLE; dmarc=pass (policy=reject) header.from=google.com; spf=pass (imf21.hostedemail.com: domain of 3zdGeYQYKCP4y0xkthmuumrk.iusrot03-ssq1giq.uxm@flex--surenb.bounces.google.com designates 209.85.222.201 as permitted sender) smtp.mailfrom=3zdGeYQYKCP4y0xkthmuumrk.iusrot03-ssq1giq.uxm@flex--surenb.bounces.google.com X-HE-Tag: 1637798348-827446 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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); } From patchwork Wed Nov 24 23:59:06 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Suren Baghdasaryan X-Patchwork-Id: 12638133 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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id BA8DDC433EF for ; Wed, 24 Nov 2021 23:59:53 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id CDB6B6B007D; Wed, 24 Nov 2021 18:59:23 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id C56326B007E; Wed, 24 Nov 2021 18:59:23 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id AF73E6B0080; Wed, 24 Nov 2021 18:59:23 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0231.hostedemail.com [216.40.44.231]) by kanga.kvack.org (Postfix) with ESMTP id A1B406B007D for ; Wed, 24 Nov 2021 18:59:23 -0500 (EST) Received: from smtpin17.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id 5FC6018126E7C for ; Wed, 24 Nov 2021 23:59:13 +0000 (UTC) X-FDA: 78845492544.17.55338F6 Received: from mail-pf1-f201.google.com (mail-pf1-f201.google.com [209.85.210.201]) by imf03.hostedemail.com (Postfix) with ESMTP id D388E300044A for ; Wed, 24 Nov 2021 23:59:09 +0000 (UTC) Received: by mail-pf1-f201.google.com with SMTP id c21-20020a62e815000000b004a29ebf0aa7so2423217pfi.2 for ; 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Wed, 24 Nov 2021 15:59:11 -0800 (PST) Date: Wed, 24 Nov 2021 15:59:06 -0800 In-Reply-To: <20211124235906.14437-1-surenb@google.com> Message-Id: <20211124235906.14437-2-surenb@google.com> Mime-Version: 1.0 References: <20211124235906.14437-1-surenb@google.com> X-Mailer: git-send-email 2.34.0.rc2.393.gf8c9666880-goog Subject: [PATCH v2 2/2] mm/oom_kill: allow process_mrelease to run under mmap_lock protection 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 X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: D388E300044A X-Stat-Signature: zr8f67wnz47bkuu7mjxyfinunedbdygy Authentication-Results: imf03.hostedemail.com; dkim=pass header.d=google.com header.s=20210112 header.b=XeEU3PAG; spf=pass (imf03.hostedemail.com: domain of 3z9GeYQYKCAIuwtgpdiqqing.eqonkpwz-oomxcem.qti@flex--surenb.bounces.google.com designates 209.85.210.201 as permitted sender) smtp.mailfrom=3z9GeYQYKCAIuwtgpdiqqing.eqonkpwz-oomxcem.qti@flex--surenb.bounces.google.com; dmarc=pass (policy=reject) header.from=google.com X-HE-Tag: 1637798349-316282 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: With exit_mmap holding mmap_write_lock during free_pgtables call, process_mrelease does not need to elevate mm->mm_users in order to prevent exit_mmap from destrying pagetables while __oom_reap_task_mm is walking the VMA tree. The change prevents process_mrelease from calling the last mmput, which can lead to waiting for IO completion in exit_aio. Fixes: 337546e83fc7 ("mm/oom_kill.c: prevent a race between process_mrelease and exit_mmap") Signed-off-by: Suren Baghdasaryan --- mm/oom_kill.c | 27 +++++++++++++++------------ 1 file changed, 15 insertions(+), 12 deletions(-) diff --git a/mm/oom_kill.c b/mm/oom_kill.c index 1ddabefcfb5a..67780386f478 100644 --- a/mm/oom_kill.c +++ b/mm/oom_kill.c @@ -1169,15 +1169,15 @@ SYSCALL_DEFINE2(process_mrelease, int, pidfd, unsigned int, flags) goto put_task; } - if (mmget_not_zero(p->mm)) { - mm = p->mm; - if (task_will_free_mem(p)) - reap = true; - else { - /* Error only if the work has not been done already */ - if (!test_bit(MMF_OOM_SKIP, &mm->flags)) - ret = -EINVAL; - } + mm = p->mm; + mmgrab(mm); + + if (task_will_free_mem(p)) + reap = true; + else { + /* Error only if the work has not been done already */ + if (!test_bit(MMF_OOM_SKIP, &mm->flags)) + ret = -EINVAL; } task_unlock(p); @@ -1188,13 +1188,16 @@ SYSCALL_DEFINE2(process_mrelease, int, pidfd, unsigned int, flags) ret = -EINTR; goto drop_mm; } - if (!__oom_reap_task_mm(mm)) + /* + * Check MMF_OOM_SKIP again under mmap_read_lock protection to ensure + * possible change in exit_mmap is seen + */ + if (!test_bit(MMF_OOM_SKIP, &mm->flags) && !__oom_reap_task_mm(mm)) ret = -EAGAIN; mmap_read_unlock(mm); drop_mm: - if (mm) - mmput(mm); + mmdrop(mm); put_task: put_task_struct(task); return ret;