From patchwork Thu Dec 9 19:13:23 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Suren Baghdasaryan X-Patchwork-Id: 12668097 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 5D516C433F5 for ; Thu, 9 Dec 2021 19:13:52 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id D93CA6B0072; Thu, 9 Dec 2021 14:13:41 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id D42096B0073; Thu, 9 Dec 2021 14:13:41 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id C09116B0074; Thu, 9 Dec 2021 14:13:41 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0058.hostedemail.com [216.40.44.58]) by kanga.kvack.org (Postfix) with ESMTP id AE1C16B0072 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=iP6OFT0YZhBctvqcWIj5MZywUhn3cHVX5RMNAeQUo1A=; b=BXHeFwUUkfzmfR409q0AKga46TTirGL+hlkc8O5Icvvtv0i4HJ0w0MkBs67H5qhuhc xXYXMQnNBR7nvI5b+vdJcyP3BIk6hfpOQ8LKQdslUVFkkK86013Hn7Bme6LtjmueZDKn o7eBCOmcGzTHs3l+cIuvOSc/Fd256DpDVKWG3Zb9GWAh5iCN3a6sCUJ+E/DOxHsN3/Ct afHqWm0eTL+ZF7++FImRIj/rUKYhrFm5zZNkbEg+0PRqKF9lMD2HTy+LCE2MyxcDWOmN e1n8omVYoD5BovHO8eSjMCUHpwdw3qfnKeztBRWmFKTHHzEYbkoy0vMRN+LC1xsSdv7a zc6Q== X-Gm-Message-State: AOAM530ijEM7btGK7zlNyW50IMO0GR+RpLEySmnXTADoy80wKSlCGJRw MThcJNdfdnYEPM5sn9mtVC4+vq7jFds= X-Google-Smtp-Source: ABdhPJwRa0DrovLmXnVJtJ/EBrf/knW3YT2e46j6n37V+4D5mBIE+WTkDPzGI87t5yBEusZSVhTpSs4h37w= X-Received: from surenb-desktop.mtv.corp.google.com ([2620:15c:211:200:8b23:8fcc:c6e4:3a65]) (user=surenb job=sendgmr) by 2002:a25:d16:: with SMTP id 22mr8606614ybn.51.1639077209831; Thu, 09 Dec 2021 11:13:29 -0800 (PST) Date: Thu, 9 Dec 2021 11:13:23 -0800 Message-Id: <20211209191325.3069345-1-surenb@google.com> Mime-Version: 1.0 X-Mailer: git-send-email 2.34.1.173.g76aa8bc2d0-goog Subject: [PATCH v5 1/3] 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: rspam07 X-Rspamd-Queue-Id: 4A85E20009 X-Stat-Signature: 4it41jtt6t91oncbzqhwomgukegutzj4 Authentication-Results: imf13.hostedemail.com; dkim=pass header.d=google.com header.s=20210112 header.b=jUTWtoDW; spf=pass (imf13.hostedemail.com: domain of 3WVWyYQYKCOAUWTGPDIQQING.EQONKPWZ-OOMXCEM.QTI@flex--surenb.bounces.google.com designates 209.85.219.202 as permitted sender) smtp.mailfrom=3WVWyYQYKCOAUWTGPDIQQING.EQONKPWZ-OOMXCEM.QTI@flex--surenb.bounces.google.com; dmarc=pass (policy=reject) header.from=google.com X-HE-Tag: 1639077210-582902 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 unlock_range, free_pgtables and remove_vma. 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 Acked-by: Michal Hocko --- changes in v5 - Corrected patch description, per Michal Hocko - Added Acked-by 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 Thu Dec 9 19:13:24 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Suren Baghdasaryan X-Patchwork-Id: 12668099 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 E0B86C433EF for ; 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Thu, 09 Dec 2021 11:13:32 -0800 (PST) Date: Thu, 9 Dec 2021 11:13:24 -0800 In-Reply-To: <20211209191325.3069345-1-surenb@google.com> Message-Id: <20211209191325.3069345-2-surenb@google.com> Mime-Version: 1.0 References: <20211209191325.3069345-1-surenb@google.com> X-Mailer: git-send-email 2.34.1.173.g76aa8bc2d0-goog Subject: [PATCH v5 2/3] mm: document locking restrictions for vm_operations_struct::close 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-Stat-Signature: po6wocnmt5ix13818jcot9381xes3ffb Authentication-Results: imf04.hostedemail.com; dkim=pass header.d=google.com header.s=20210112 header.b=pRDHRPMc; dmarc=pass (policy=reject) header.from=google.com; spf=pass (imf04.hostedemail.com: domain of 3XFWyYQYKCOMXZWJSGLTTLQJ.HTRQNSZc-RRPaFHP.TWL@flex--surenb.bounces.google.com designates 209.85.219.201 as permitted sender) smtp.mailfrom=3XFWyYQYKCOMXZWJSGLTTLQJ.HTRQNSZc-RRPaFHP.TWL@flex--surenb.bounces.google.com X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 3CBA440004 X-HE-Tag: 1639077213-278903 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: Add comments for vm_operations_struct::close documenting locking requirements for this callback and its callers. Signed-off-by: Suren Baghdasaryan Acked-by: Michal Hocko --- changes in v5 - Added Acked-by include/linux/mm.h | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/include/linux/mm.h b/include/linux/mm.h index a7e4a9e7d807..b9b88ba7564b 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); + /** + * @close: Called when the VMA is being removed from the MM. + * Context: User context. May sleep. Caller holds mmap_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); From patchwork Thu Dec 9 19:13:25 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Suren Baghdasaryan X-Patchwork-Id: 12668101 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 1CA2CC433F5 for ; Thu, 9 Dec 2021 19:14:44 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 30B926B0074; Thu, 9 Dec 2021 14:13:46 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 2BAFE6B0075; Thu, 9 Dec 2021 14:13:46 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 15BFE6B0078; 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Thu, 09 Dec 2021 11:13:34 -0800 (PST) Date: Thu, 9 Dec 2021 11:13:25 -0800 In-Reply-To: <20211209191325.3069345-1-surenb@google.com> Message-Id: <20211209191325.3069345-3-surenb@google.com> Mime-Version: 1.0 References: <20211209191325.3069345-1-surenb@google.com> X-Mailer: git-send-email 2.34.1.173.g76aa8bc2d0-goog Subject: [PATCH v5 3/3] 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-Queue-Id: 881B540004 Authentication-Results: imf17.hostedemail.com; dkim=pass header.d=google.com header.s=20210112 header.b=SUl8Nhso; spf=pass (imf17.hostedemail.com: domain of 3XlWyYQYKCOUZbYLUINVVNSL.JVTSPUbe-TTRcHJR.VYN@flex--surenb.bounces.google.com designates 209.85.219.202 as permitted sender) smtp.mailfrom=3XlWyYQYKCOUZbYLUINVVNSL.JVTSPUbe-TTRcHJR.VYN@flex--surenb.bounces.google.com; dmarc=pass (policy=reject) header.from=google.com X-Rspamd-Server: rspam04 X-Stat-Signature: the1rkod4zfz79488jxqknfkoo8wu3d3 X-HE-Tag: 1639077213-213254 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. Signed-off-by: Suren Baghdasaryan Acked-by: Michal Hocko Reviewed-by: Jason Gunthorpe --- changes in v5 - Removed Fixes: tag, per Michal Hocko - Added Acked-by's 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;