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[209.132.180.67]) by mx.google.com with ESMTP id b21si390173ots.38.2020.02.12.06.49.49; Wed, 12 Feb 2020 06:50:02 -0800 (PST) Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67; Authentication-Results: mx.google.com; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=fail (p=NONE sp=QUARANTINE dis=NONE) header.from=gmail.com Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728410AbgBLOt0 (ORCPT + 99 others); Wed, 12 Feb 2020 09:49:26 -0500 Received: from monster.unsafe.ru ([5.9.28.80]:46690 "EHLO mail.unsafe.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727101AbgBLOt0 (ORCPT ); Wed, 12 Feb 2020 09:49:26 -0500 Received: from comp-core-i7-2640m-0182e6 (nat-pool-brq-t.redhat.com [213.175.37.10]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.unsafe.ru (Postfix) with ESMTPSA id AFA2DC61AB0; Wed, 12 Feb 2020 14:49:22 +0000 (UTC) Date: Wed, 12 Feb 2020 15:49:21 +0100 From: Alexey Gladkov To: "Eric W. Biederman" Cc: LKML , Kernel Hardening , Linux API , Linux FS Devel , Linux Security Module , Akinobu Mita , Alexander Viro , Alexey Dobriyan , Andrew Morton , Andy Lutomirski , Daniel Micay , Djalal Harouni , "Dmitry V . Levin" , Greg Kroah-Hartman , Ingo Molnar , "J . Bruce Fields" , Jeff Layton , Jonathan Corbet , Kees Cook , Linus Torvalds , Oleg Nesterov , Solar Designer Subject: Re: [PATCH v8 07/11] proc: flush task dcache entries from all procfs instances Message-ID: <20200212144921.sykucj4mekcziicz@comp-core-i7-2640m-0182e6> Mail-Followup-To: "Eric W. Biederman" , LKML , Kernel Hardening , Linux API , Linux FS Devel , Linux Security Module , Akinobu Mita , Alexander Viro , Alexey Dobriyan , Andrew Morton , Andy Lutomirski , Daniel Micay , Djalal Harouni , "Dmitry V . Levin" , Greg Kroah-Hartman , Ingo Molnar , "J . Bruce Fields" , Jeff Layton , Jonathan Corbet , Kees Cook , Linus Torvalds , Oleg Nesterov , Solar Designer References: <20200210150519.538333-1-gladkov.alexey@gmail.com> <20200210150519.538333-8-gladkov.alexey@gmail.com> <87v9odlxbr.fsf@x220.int.ebiederm.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87v9odlxbr.fsf@x220.int.ebiederm.org> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Feb 10, 2020 at 07:36:08PM -0600, Eric W. Biederman wrote: > Alexey Gladkov writes: > > > This allows to flush dcache entries of a task on multiple procfs mounts > > per pid namespace. > > > > The RCU lock is used because the number of reads at the task exit time > > is much larger than the number of procfs mounts. > > A couple of quick comments. > > > Cc: Kees Cook > > Cc: Andy Lutomirski > > Signed-off-by: Djalal Harouni > > Suggested-by: Linus Torvalds > > Signed-off-by: Alexey Gladkov > > --- > > fs/proc/base.c | 20 +++++++++++++++----- > > fs/proc/root.c | 27 ++++++++++++++++++++++++++- > > include/linux/pid_namespace.h | 2 ++ > > include/linux/proc_fs.h | 2 ++ > > 4 files changed, 45 insertions(+), 6 deletions(-) > > > > diff --git a/fs/proc/base.c b/fs/proc/base.c > > index 4ccb280a3e79..24b7c620ded3 100644 > > --- a/fs/proc/base.c > > +++ b/fs/proc/base.c > > @@ -3133,7 +3133,7 @@ static const struct inode_operations proc_tgid_base_inode_operations = { > > .permission = proc_pid_permission, > > }; > > > > -static void proc_flush_task_mnt(struct vfsmount *mnt, pid_t pid, pid_t tgid) > > +static void proc_flush_task_mnt_root(struct dentry *mnt_root, pid_t pid, pid_t tgid) > Perhaps just rename things like: > > +static void proc_flush_task_root(struct dentry *root, pid_t pid, pid_t tgid) > > { > > I don't think the mnt_ prefix conveys any information, and it certainly > makes everything longer and more cumbersome. > > > struct dentry *dentry, *leader, *dir; > > char buf[10 + 1]; > > @@ -3142,7 +3142,7 @@ static void proc_flush_task_mnt(struct vfsmount *mnt, pid_t pid, pid_t tgid) > > name.name = buf; > > name.len = snprintf(buf, sizeof(buf), "%u", pid); > > /* no ->d_hash() rejects on procfs */ > > - dentry = d_hash_and_lookup(mnt->mnt_root, &name); > > + dentry = d_hash_and_lookup(mnt_root, &name); > > if (dentry) { > > d_invalidate(dentry); > > dput(dentry); > > @@ -3153,7 +3153,7 @@ static void proc_flush_task_mnt(struct vfsmount *mnt, pid_t pid, pid_t tgid) > > > > name.name = buf; > > name.len = snprintf(buf, sizeof(buf), "%u", tgid); > > - leader = d_hash_and_lookup(mnt->mnt_root, &name); > > + leader = d_hash_and_lookup(mnt_root, &name); > > if (!leader) > > goto out; > > > > @@ -3208,14 +3208,24 @@ void proc_flush_task(struct task_struct *task) > > int i; > > struct pid *pid, *tgid; > > struct upid *upid; > > + struct dentry *mnt_root; > > + struct proc_fs_info *fs_info; > > > > pid = task_pid(task); > > tgid = task_tgid(task); > > > > for (i = 0; i <= pid->level; i++) { > > upid = &pid->numbers[i]; > > - proc_flush_task_mnt(upid->ns->proc_mnt, upid->nr, > > - tgid->numbers[i].nr); > > + > > + rcu_read_lock(); > > + list_for_each_entry_rcu(fs_info, &upid->ns->proc_mounts, pidns_entry) { > > + mnt_root = fs_info->m_super->s_root; > > + proc_flush_task_mnt_root(mnt_root, upid->nr, tgid->numbers[i].nr); > > + } > > + rcu_read_unlock(); > > + > > + mnt_root = upid->ns->proc_mnt->mnt_root; > > + proc_flush_task_mnt_root(mnt_root, upid->nr, tgid->numbers[i].nr); > > I don't think this following of proc_mnt is needed. It certainly > shouldn't be. The loop through all of the super blocks should be > enough. Yes, thanks! > Once this change goes through. UML can be given it's own dedicated > proc_mnt for the initial pid namespace, and proc_mnt can be removed > entirely. After you deleted the old sysctl syscall we could probably do it. > Unless something has changed recently UML is the only other user of > pid_ns->proc_mnt. That proc_mnt really only exists to make the loop in > proc_flush_task easy to write. Now I think, is there any way to get rid of proc_mounts or even proc_flush_task somehow. > It also probably makes sense to take the rcu_read_lock() over > that entire for loop. Al Viro pointed out to me that I cannot use rcu locks here :( -- Rgrds, legion