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 X-Spam-Level: X-Spam-Status: No, score=-7.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 425DEC10F05 for ; Tue, 26 Mar 2019 08:18:21 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 0721720830 for ; Tue, 26 Mar 2019 08:18:20 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0721720830 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=virtuozzo.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 9C2DB6B0007; Tue, 26 Mar 2019 04:18:20 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 94AC16B0008; Tue, 26 Mar 2019 04:18:20 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 839E56B000A; Tue, 26 Mar 2019 04:18:20 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from mail-lf1-f70.google.com (mail-lf1-f70.google.com [209.85.167.70]) by kanga.kvack.org (Postfix) with ESMTP id 1D1666B0007 for ; Tue, 26 Mar 2019 04:18:20 -0400 (EDT) Received: by mail-lf1-f70.google.com with SMTP id s26so1038955lfc.7 for ; Tue, 26 Mar 2019 01:18:20 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-original-authentication-results:x-gm-message-state:subject:from :to:cc:references:message-id:date:user-agent:mime-version :in-reply-to:content-language:content-transfer-encoding; bh=Fc7QEnSMJOCWnX0b0b1JDUi3K89Px3teW0qf+Ot4o6U=; b=gIhNJPuro+5oVuuUXKpA9VtSxoN3lyeX3Nq42rQnMsiUzbh6/YIq7vmXKiCN6Pr/2r nTwG0OeEqeEF42cxkD+XqDwzh7tFJncGyIY6eLxUC5r59dFG9uUZo3FtBxlFJCH647OZ 5RIghBw0rB+q40N03e0eIzEoS8GbzK3sh00/4UkgBaEfkhIoN/gzcyPN8/qVgVFYbphE HTptkLjEjyrROdyrHiGav1cLy++6IbJE/lEyumgaGcprzUpxHksjpVsPBbNs89IgMby1 kpnarIS9XN+AbH9ByhqqXW/pPH2hiSbzRiTORbtkI40LJz+h8fHh0ba3e84tBBjsR1nd 1EVQ== X-Original-Authentication-Results: mx.google.com; spf=pass (google.com: domain of ktkhai@virtuozzo.com designates 185.231.240.75 as permitted sender) smtp.mailfrom=ktkhai@virtuozzo.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=virtuozzo.com X-Gm-Message-State: APjAAAUZaPdtwNPhavyYc8zbqPmilph8zNR8edgZ0b8yxPHszO3mvxUw X+Ds274C+MWxx92EyY+ESqls5erYoru+CLZRNhCFw1CBVjJTPhuEEp2v9a0IMT23nTx5XF5/c5Y NblyGhNPfP0bCfv0gy78swWtopBMIvaqTfWWUnd6uMTBocMD0/6JgJhg6DUOZehPyxQ== X-Received: by 2002:ac2:569b:: with SMTP id 27mr15679581lfr.24.1553588299309; Tue, 26 Mar 2019 01:18:19 -0700 (PDT) X-Google-Smtp-Source: APXvYqy99+LRr2xof0cfGdqC0H81Q9NcJnCgAFLU82QEmha1f/7sqDeqUbpO3CRIli2iDml0EA33 X-Received: by 2002:ac2:569b:: with SMTP id 27mr15679459lfr.24.1553588296726; Tue, 26 Mar 2019 01:18:16 -0700 (PDT) ARC-Seal: i=1; a=rsa-sha256; t=1553588296; cv=none; d=google.com; s=arc-20160816; b=tWmVmJ7knzX+aJ306aZ0NP3o+oJ5iPuKgZBnD/o93Jnvi/LJ39wIIEtCZTRmBcZLks yuB+zoHlgsFmYJ1JFSTb8P+w/QkQ/X052VyB5W9EiYoGqRviGPwrfDlP/JvCPg7fPIde CIN4eOX8T9o+qiu3gk9JAwdwDyXN38WORFgmZYTzxyNYvvypdrfV4nJY9ZP0zj0GwCr6 e7u40a1dmes07G310D22GNhnqNhgSve6ksYzFcxJacxIRZVGpmtFev9EQdk19IOBR1Wp NiAr223X8i3hCBnUWeuLtMAMXbM80tQP7zIa0rcZxBvWV3kjjckZ/sbTkPOFg7Xr3l/U YveA== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=content-transfer-encoding:content-language:in-reply-to:mime-version :user-agent:date:message-id:references:cc:to:from:subject; bh=Fc7QEnSMJOCWnX0b0b1JDUi3K89Px3teW0qf+Ot4o6U=; b=ICiCc1AgAQE6vZqrWVnz0nWZtDUR59FTBkbgJBEImFAb1RlRw6mNFCY+OmM2E8mMpz FLY4KLvhESEZJwsRVNa/uqP/WVuKd6TIVZbrMkINyNkmUk4B9O2zW02SNxQKrGN/tq0A l43MzPbBY8Xq9aUAs41dDaB7xHJYoPg9skECJyjC2sPuGpulJGgZmYOH6BdnUCmkxXuv RINuYBAFUhCK42yZ6SjubVqmiyWXxGmYOskiaxXLnXB+tH8rN0aabingZrN/Yi6HEJH4 vADv1UiwE7O9JrenuZWJZHLfH4HYM9SSeT7AQXJ48miLNAy7nHXYahcvv1Oc5KkzxLzM 7dTw== ARC-Authentication-Results: i=1; mx.google.com; spf=pass (google.com: domain of ktkhai@virtuozzo.com designates 185.231.240.75 as permitted sender) smtp.mailfrom=ktkhai@virtuozzo.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=virtuozzo.com Received: from relay.sw.ru (relay.sw.ru. [185.231.240.75]) by mx.google.com with ESMTPS id z23si12831979ljj.24.2019.03.26.01.18.16 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 26 Mar 2019 01:18:16 -0700 (PDT) Received-SPF: pass (google.com: domain of ktkhai@virtuozzo.com designates 185.231.240.75 as permitted sender) client-ip=185.231.240.75; Authentication-Results: mx.google.com; spf=pass (google.com: domain of ktkhai@virtuozzo.com designates 185.231.240.75 as permitted sender) smtp.mailfrom=ktkhai@virtuozzo.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=virtuozzo.com Received: from [172.16.25.169] by relay.sw.ru with esmtp (Exim 4.91) (envelope-from ) id 1h8hHb-00080A-6M; Tue, 26 Mar 2019 11:18:07 +0300 Subject: Re: [PATCH 1/2] userfaultfd: use RCU to free the task struct when fork fails From: Kirill Tkhai To: Andrea Arcangeli , Andrew Morton Cc: linux-mm@kvack.org, zhong jiang , syzkaller-bugs@googlegroups.com, syzbot+cbb52e396df3e565ab02@syzkaller.appspotmail.com, Mike Rapoport , Mike Kravetz , Peter Xu , Dmitry Vyukov References: <20190325225636.11635-1-aarcange@redhat.com> <20190325225636.11635-2-aarcange@redhat.com> <29e5c5ed-5efb-fe02-45a5-97903c88e0ec@virtuozzo.com> Message-ID: <303ae124-dc01-0989-7cca-39ec7331d1be@virtuozzo.com> Date: Tue, 26 Mar 2019 11:18:05 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.5.1 MIME-Version: 1.0 In-Reply-To: <29e5c5ed-5efb-fe02-45a5-97903c88e0ec@virtuozzo.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit 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: On 26.03.2019 11:07, Kirill Tkhai wrote: > On 26.03.2019 01:56, Andrea Arcangeli wrote: >> MEMCG depends on the task structure not to be freed under >> rcu_read_lock() in get_mem_cgroup_from_mm() after it dereferences >> mm->owner. >> >> An alternate possible fix would be to defer the delivery of the >> userfaultfd contexts to the monitor until after fork() is guaranteed >> to succeed. Such a change would require more changes because it would >> create a strict ordering dependency where the uffd methods would need >> to be called beyond the last potentially failing branch in order to be >> safe. This solution as opposed only adds the dependency to common code >> to set mm->owner to NULL and to free the task struct that was pointed >> by mm->owner with RCU, if fork ends up failing. The userfaultfd >> methods can still be called anywhere during the fork runtime and the >> monitor will keep discarding orphaned "mm" coming from failed forks in >> userland. >> >> This race condition couldn't trigger if CONFIG_MEMCG was set =n at >> build time. >> >> Fixes: 893e26e61d04 ("userfaultfd: non-cooperative: Add fork() event") >> Cc: stable@kernel.org >> Tested-by: zhong jiang >> Reported-by: syzbot+cbb52e396df3e565ab02@syzkaller.appspotmail.com >> Signed-off-by: Andrea Arcangeli >> --- >> kernel/fork.c | 34 ++++++++++++++++++++++++++++++++-- >> 1 file changed, 32 insertions(+), 2 deletions(-) >> >> diff --git a/kernel/fork.c b/kernel/fork.c >> index 9dcd18aa210b..a19790e27afd 100644 >> --- a/kernel/fork.c >> +++ b/kernel/fork.c >> @@ -952,6 +952,15 @@ static void mm_init_aio(struct mm_struct *mm) >> #endif >> } >> >> +static __always_inline void mm_clear_owner(struct mm_struct *mm, >> + struct task_struct *p) >> +{ >> +#ifdef CONFIG_MEMCG >> + if (mm->owner == p) >> + WRITE_ONCE(mm->owner, NULL); >> +#endif >> +} >> + >> static void mm_init_owner(struct mm_struct *mm, struct task_struct *p) >> { >> #ifdef CONFIG_MEMCG >> @@ -1331,6 +1340,7 @@ static struct mm_struct *dup_mm(struct task_struct *tsk) >> free_pt: >> /* don't put binfmt in mmput, we haven't got module yet */ >> mm->binfmt = NULL; >> + mm_init_owner(mm, NULL); >> mmput(mm); >> >> fail_nomem: >> @@ -1662,6 +1672,24 @@ static inline void rcu_copy_process(struct task_struct *p) >> #endif /* #ifdef CONFIG_TASKS_RCU */ >> } >> >> +#ifdef CONFIG_MEMCG >> +static void __delayed_free_task(struct rcu_head *rhp) >> +{ >> + struct task_struct *tsk = container_of(rhp, struct task_struct, rcu); >> + >> + free_task(tsk); >> +} >> +#endif /* CONFIG_MEMCG */ >> + >> +static __always_inline void delayed_free_task(struct task_struct *tsk) >> +{ >> +#ifdef CONFIG_MEMCG >> + call_rcu(&tsk->rcu, __delayed_free_task); >> +#else /* CONFIG_MEMCG */ >> + free_task(tsk); >> +#endif /* CONFIG_MEMCG */ >> +} >> + >> /* >> * This creates a new process as a copy of the old one, >> * but does not actually start it yet. >> @@ -2123,8 +2151,10 @@ static __latent_entropy struct task_struct *copy_process( >> bad_fork_cleanup_namespaces: >> exit_task_namespaces(p); >> bad_fork_cleanup_mm: >> - if (p->mm) >> + if (p->mm) { >> + mm_clear_owner(p->mm, p); >> mmput(p->mm); >> + } >> bad_fork_cleanup_signal: >> if (!(clone_flags & CLONE_THREAD)) >> free_signal_struct(p->signal); >> @@ -2155,7 +2185,7 @@ static __latent_entropy struct task_struct *copy_process( >> bad_fork_free: >> p->state = TASK_DEAD; >> put_task_stack(p); >> - free_task(p); >> + delayed_free_task(p); > > Can't call_rcu(&p->rcu, delayed_put_task_struct) be used instead this? I mean: refcount_set(&tsk->usage, 2); call_rcu(&p->rcu, delayed_put_task_struct); And: diff --git a/kernel/fork.c b/kernel/fork.c index 3c516c6f7ce4..27cdf61b51a1 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -715,7 +715,9 @@ static inline void put_signal_struct(struct signal_struct *sig) void __put_task_struct(struct task_struct *tsk) { - WARN_ON(!tsk->exit_state); + if (!tsk->exit_state) + /* Cleanup of copy_process() */ + goto free; WARN_ON(refcount_read(&tsk->usage)); WARN_ON(tsk == current); @@ -727,6 +729,7 @@ void __put_task_struct(struct task_struct *tsk) put_signal_struct(tsk->signal); if (!profile_handoff_task(tsk)) +free: free_task(tsk); } EXPORT_SYMBOL_GPL(__put_task_struct);