From patchwork Tue Dec 7 21:50:30 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Suren Baghdasaryan X-Patchwork-Id: 12662803 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 AE9FDC433F5 for ; Tue, 7 Dec 2021 21:50:57 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 3E2DE6B0072; Tue, 7 Dec 2021 16:50:47 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 36B546B0073; Tue, 7 Dec 2021 16:50:47 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 20C8B6B0074; Tue, 7 Dec 2021 16:50:47 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0031.hostedemail.com [216.40.44.31]) by kanga.kvack.org (Postfix) with ESMTP id 0B33E6B0072 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=eHNFJYUS7s98EY2lIfhsBH85e2eiRptEG86rTMjby3I=; b=LNK5tiU2auZdCAqfWJSzE6mgEUyDbiPhAEw7VahtVygX8kfDyYmbCc+Ol/kMU0r3fb /4FOh65moT6zYaW+BQ8adlx4ldcQ7ifUIg6PZ81pqD+6px0kfqt9mehf/x6+K6oTw88Z b8YHBz/nMTQQv+HGEJYX9Klcsn2q5pJSfEmXZ2RswNq15nxRZqEZIB9ncgdMxBOSPvhX 9VpEKu+NBXvCOJ24R/6nRCn2FAmjNQ6qsDIAZ+nm7Ul3uGe0NztO0OJJYc7CyMgtWvE8 mjZqRG3QFXV8X+6PS0wd2mbKBsXl5JS9rPex3tyy1Q+v8Eym0uTjFYZRkMwKQP9KP7GS LNbw== X-Gm-Message-State: AOAM530HaaqQ/L5qvg1DzYh5kVBvbl/ECM0U8DHakN4ldIGG8Nsg0eGa JRHa7QoI0/srRtbo/x+eO/kioOtP1Zc= X-Google-Smtp-Source: ABdhPJxYG9QPsqoonw9DmkWvWnN0thm87lG8wB6LGNRWmRlEYY2T38W/3oBLw3kxcUbqL60HyUffvx8Aqbc= X-Received: from surenb-desktop.mtv.corp.google.com ([2620:15c:211:200:c2df:fc7c:ed5e:6133]) (user=surenb job=sendgmr) by 2002:a25:d756:: with SMTP id o83mr52328152ybg.394.1638913835585; Tue, 07 Dec 2021 13:50:35 -0800 (PST) Date: Tue, 7 Dec 2021 13:50:30 -0800 Message-Id: <20211207215031.2251719-1-surenb@google.com> Mime-Version: 1.0 X-Mailer: git-send-email 2.34.1.400.ga245620fadb-goog Subject: [PATCH v3 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: rspam03 X-Rspamd-Queue-Id: 6522520002 X-Stat-Signature: dibu5fnyomyotgaw83nf4nyj6ffezqq5 Authentication-Results: imf03.hostedemail.com; dkim=pass header.d=google.com header.s=20210112 header.b=RNbBJEbi; spf=pass (imf03.hostedemail.com: domain of 3K9evYQYKCKwegdQZNSaaSXQ.OaYXUZgj-YYWhMOW.adS@flex--surenb.bounces.google.com designates 209.85.219.202 as permitted sender) smtp.mailfrom=3K9evYQYKCKwegdQZNSaaSXQ.OaYXUZgj-YYWhMOW.adS@flex--surenb.bounces.google.com; dmarc=pass (policy=reject) header.from=google.com X-HE-Tag: 1638913836-530768 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 and remove_vma. 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. Before this patch, remove_vma used to be called with no locks held, however with fput being executed asynchronously and vm_ops->close not being allowed to hold mmap_lock (it is called from __split_vma with mmap_sem held for write), changing that should be fine. 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 v3 - Amended patch description to explain why remove_vma can be called while holding mmap_write_lock, per Michal Hocko - Added a comment for vm_operations_struct::close, documenting restriction for taking mmap_lock in the callback, per Michal Hocko and Matthew Wilcox include/linux/mm.h | 4 ++++ mm/mmap.c | 16 ++++++++-------- 2 files changed, 12 insertions(+), 8 deletions(-) diff --git a/include/linux/mm.h b/include/linux/mm.h index a7e4a9e7d807..97e1a05c3b2c 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -577,6 +577,10 @@ enum page_entry_size { */ struct vm_operations_struct { void (*open)(struct vm_area_struct * area); + /* + * Called with mmap_lock lock held for write from __split_vma and + * remove_vma, therefore should never take that lock. + */ void (*close)(struct vm_area_struct * area); /* Called any time before splitting to check if it's allowed */ int (*may_split)(struct vm_area_struct *area, unsigned long addr); 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 Tue Dec 7 21:50:31 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Suren Baghdasaryan X-Patchwork-Id: 12662805 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 68D84C433EF for ; Tue, 7 Dec 2021 21:51:14 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 89E386B0073; 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Tue, 07 Dec 2021 13:50:38 -0800 (PST) Date: Tue, 7 Dec 2021 13:50:31 -0800 In-Reply-To: <20211207215031.2251719-1-surenb@google.com> Message-Id: <20211207215031.2251719-2-surenb@google.com> Mime-Version: 1.0 References: <20211207215031.2251719-1-surenb@google.com> X-Mailer: git-send-email 2.34.1.400.ga245620fadb-goog Subject: [PATCH v3 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: rspam03 X-Rspamd-Queue-Id: C268940003 X-Stat-Signature: q38oof6a66mbckasrgsobe9hrhfb5ebs Authentication-Results: imf01.hostedemail.com; dkim=pass header.d=google.com header.s=20210112 header.b=TSJWEN5R; spf=pass (imf01.hostedemail.com: domain of 3LtevYQYKCK8hjgTcQVddVaT.RdbaXcjm-bbZkPRZ.dgV@flex--surenb.bounces.google.com designates 209.85.219.202 as permitted sender) smtp.mailfrom=3LtevYQYKCK8hjgTcQVddVaT.RdbaXcjm-bbZkPRZ.dgV@flex--surenb.bounces.google.com; dmarc=pass (policy=reject) header.from=google.com X-HE-Tag: 1638913838-821543 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;