From: Alexey Gladkov <gladkov.alexey@gmail.com>
To: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: LKML <linux-kernel@vger.kernel.org>,
Kernel Hardening <kernel-hardening@lists.openwall.com>,
Linux API <linux-api@vger.kernel.org>,
Linux FS Devel <linux-fsdevel@vger.kernel.org>,
Linux Security Module <linux-security-module@vger.kernel.org>,
Akinobu Mita <akinobu.mita@gmail.com>,
Alexander Viro <viro@zeniv.linux.org.uk>,
Alexey Dobriyan <adobriyan@gmail.com>,
Andrew Morton <akpm@linux-foundation.org>,
Andy Lutomirski <luto@kernel.org>,
Daniel Micay <danielmicay@gmail.com>,
Djalal Harouni <tixxdz@gmail.com>,
"Dmitry V . Levin" <ldv@altlinux.org>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Ingo Molnar <mingo@kernel.org>,
"J . Bruce Fields" <bfields@fieldses.org>,
Jeff Layton <jlayton@poochiereds.net>,
Jonathan Corbet <corbet@lwn.net>,
Kees Cook <keescook@chromium.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
Oleg Nesterov <oleg@redhat.com>,
Solar Designer <solar@openwall.com>
Subject: Re: [PATCH v8 07/11] proc: flush task dcache entries from all procfs instances
Date: Wed, 12 Feb 2020 18:08:37 +0100 [thread overview]
Message-ID: <20200212170836.kiqogl4cqdpyjjk3@comp-core-i7-2640m-0182e6> (raw)
In-Reply-To: <87tv3vkg1a.fsf@x220.int.ebiederm.org>
On Wed, Feb 12, 2020 at 08:59:29AM -0600, Eric W. Biederman wrote:
> Alexey Gladkov <gladkov.alexey@gmail.com> writes:
>
> > On Mon, Feb 10, 2020 at 07:36:08PM -0600, Eric W. Biederman wrote:
> >> Alexey Gladkov <gladkov.alexey@gmail.com> 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 <keescook@chromium.org>
> >> > Cc: Andy Lutomirski <luto@kernel.org>
> >> > Signed-off-by: Djalal Harouni <tixxdz@gmail.com>
> >> > Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
> >> > Signed-off-by: Alexey Gladkov <gladkov.alexey@gmail.com>
> >> > ---
> >> > 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 :(
>
> Fundamentally proc_flush_task is an optimization. Just getting rid of
> dentries earlier. At least at one point it was an important
> optimization because the old process dentries would just sit around
> doing nothing for anyone.
>
> I wonder if instead of invalidating specific dentries we could instead
> fire wake up a shrinker and point it at one or more instances of proc.
>
> The practical challenge I see is something might need to access the
> dentries to see that they are invalid.
>
> We definitely could try without this optimization and see what happens.
When Linus said that a semaphore for proc_mounts is a bad idea, I tried
to come up with some kind of asynchronous way to clear it per superblock.
I gave up with the asynchronous GC because userspace can quite easily get
ahead of it.
Without this optimization the kernel starts to consume a lot of memory
during intensive reading /proc. I tried to do:
while :; do
for x in `seq 0 9`; do sleep 0.1; done;
ls /proc/[0-9]*;
done >/dev/null;
and memory consumption went up without proc_flush_task. Since we have
mounted procfs in each container, this is dangerous.
--
Rgrds, legion
next prev parent reply other threads:[~2020-02-12 17:08 UTC|newest]
Thread overview: 85+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-10 15:05 [PATCH v8 00/11] proc: modernize proc to support multiple private instances Alexey Gladkov
2020-02-10 15:05 ` [PATCH v8 01/11] proc: Rename struct proc_fs_info to proc_fs_opts Alexey Gladkov
2020-02-10 15:05 ` [PATCH v8 02/11] proc: add proc_fs_info struct to store proc information Alexey Gladkov
2020-02-10 15:05 ` [PATCH v8 03/11] proc: move /proc/{self|thread-self} dentries to proc_fs_info Alexey Gladkov
2020-02-10 18:23 ` Andy Lutomirski
2020-02-12 15:00 ` Alexey Gladkov
2020-02-10 15:05 ` [PATCH v8 04/11] proc: move hide_pid, pid_gid from pid_namespace " Alexey Gladkov
2020-02-10 15:05 ` [PATCH v8 05/11] proc: add helpers to set and get proc hidepid and gid mount options Alexey Gladkov
2020-02-10 18:30 ` Andy Lutomirski
2020-02-12 14:57 ` Alexey Gladkov
2020-02-10 15:05 ` [PATCH v8 06/11] proc: support mounting procfs instances inside same pid namespace Alexey Gladkov
2020-02-10 15:05 ` [PATCH v8 07/11] proc: flush task dcache entries from all procfs instances Alexey Gladkov
2020-02-10 17:46 ` Linus Torvalds
2020-02-10 19:23 ` Al Viro
2020-02-11 1:36 ` Eric W. Biederman
2020-02-11 4:01 ` Eric W. Biederman
2020-02-12 14:49 ` Alexey Gladkov
2020-02-12 14:59 ` Eric W. Biederman
2020-02-12 17:08 ` Alexey Gladkov [this message]
2020-02-12 18:45 ` Linus Torvalds
2020-02-12 19:16 ` Eric W. Biederman
2020-02-12 19:49 ` Linus Torvalds
2020-02-12 20:03 ` Al Viro
2020-02-12 20:35 ` Linus Torvalds
2020-02-12 20:38 ` Al Viro
2020-02-12 20:41 ` Al Viro
2020-02-12 21:02 ` Linus Torvalds
2020-02-12 21:46 ` Eric W. Biederman
2020-02-13 0:48 ` Linus Torvalds
2020-02-13 4:37 ` Eric W. Biederman
2020-02-13 5:55 ` Al Viro
2020-02-13 21:30 ` Linus Torvalds
2020-02-13 22:23 ` Al Viro
2020-02-13 22:47 ` Linus Torvalds
2020-02-14 14:15 ` Eric W. Biederman
2020-02-14 3:48 ` Eric W. Biederman
2020-02-20 20:46 ` [PATCH 0/7] proc: Dentry flushing without proc_mnt Eric W. Biederman
2020-02-20 20:47 ` [PATCH 1/7] proc: Rename in proc_inode rename sysctl_inodes sibling_inodes Eric W. Biederman
2020-02-20 20:48 ` [PATCH 2/7] proc: Generalize proc_sys_prune_dcache into proc_prune_siblings_dcache Eric W. Biederman
2020-02-20 20:49 ` [PATCH 3/7] proc: Mov rcu_read_(lock|unlock) in proc_prune_siblings_dcache Eric W. Biederman
2020-02-20 22:33 ` Linus Torvalds
2020-02-20 20:49 ` [PATCH 4/7] proc: Use d_invalidate " Eric W. Biederman
2020-02-20 22:43 ` Linus Torvalds
2020-02-20 22:54 ` Al Viro
2020-02-20 23:00 ` Linus Torvalds
2020-02-20 23:03 ` Al Viro
2020-02-20 23:39 ` Eric W. Biederman
2020-02-20 20:51 ` [PATCH 5/7] proc: Clear the pieces of proc_inode that proc_evict_inode cares about Eric W. Biederman
2020-02-20 20:52 ` [PATCH 6/7] proc: Use a list of inodes to flush from proc Eric W. Biederman
2020-02-20 20:52 ` [PATCH 7/7] proc: Ensure we see the exit of each process tid exactly once Eric W. Biederman
2020-02-21 16:50 ` Oleg Nesterov
2020-02-22 15:46 ` Eric W. Biederman
2020-02-20 23:02 ` [PATCH 0/7] proc: Dentry flushing without proc_mnt Linus Torvalds
2020-02-20 23:07 ` Al Viro
2020-02-20 23:37 ` Eric W. Biederman
2020-02-24 16:25 ` [PATCH v2 0/6] " Eric W. Biederman
2020-02-24 16:26 ` [PATCH v2 1/6] proc: Rename in proc_inode rename sysctl_inodes sibling_inodes Eric W. Biederman
2020-02-24 16:27 ` [PATCH v2 2/6] proc: Generalize proc_sys_prune_dcache into proc_prune_siblings_dcache Eric W. Biederman
2020-02-24 16:27 ` [PATCH v2 3/6] proc: In proc_prune_siblings_dcache cache an aquired super block Eric W. Biederman
2020-02-24 16:28 ` [PATCH v2 4/6] proc: Use d_invalidate in proc_prune_siblings_dcache Eric W. Biederman
2020-02-24 16:28 ` [PATCH v2 5/6] proc: Clear the pieces of proc_inode that proc_evict_inode cares about Eric W. Biederman
2020-02-24 16:29 ` [PATCH v2 6/6] proc: Use a list of inodes to flush from proc Eric W. Biederman
2020-02-28 20:17 ` [PATCH 0/3] proc: Actually honor the mount options Eric W. Biederman
2020-02-28 20:18 ` [PATCH 1/3] uml: Don't consult current to find the proc_mnt in mconsole_proc Eric W. Biederman
2020-02-28 20:18 ` [PATCH 2/3] uml: Create a private mount of proc for mconsole Eric W. Biederman
2020-02-28 20:30 ` Christian Brauner
2020-02-28 21:28 ` Eric W. Biederman
2020-02-28 21:59 ` Christian Brauner
2020-02-28 20:19 ` [PATCH 3/3] proc: Remove the now unnecessary internal mount of proc Eric W. Biederman
2020-02-28 20:39 ` Christian Brauner
2020-02-28 21:40 ` Eric W. Biederman
2020-02-28 22:34 ` [PATCH 4/3] pid: Improve the comment about waiting in zap_pid_ns_processes Eric W. Biederman
2020-02-29 2:59 ` Christian Brauner
2020-02-14 3:49 ` [PATCH v8 07/11] proc: flush task dcache entries from all procfs instances Eric W. Biederman
2020-02-12 19:47 ` Al Viro
2020-02-11 22:45 ` Al Viro
2020-02-12 14:26 ` Alexey Gladkov
2020-02-10 15:05 ` [PATCH v8 08/11] proc: instantiate only pids that we can ptrace on 'hidepid=4' mount option Alexey Gladkov
2020-02-10 16:29 ` Jordan Glover
2020-02-12 14:34 ` Alexey Gladkov
2020-02-10 15:05 ` [PATCH v8 09/11] proc: add option to mount only a pids subset Alexey Gladkov
2020-02-10 15:05 ` [PATCH v8 10/11] docs: proc: add documentation for "hidepid=4" and "subset=pidfs" options and new mount behavior Alexey Gladkov
2020-02-10 18:29 ` Andy Lutomirski
2020-02-12 16:03 ` Alexey Gladkov
2020-02-10 15:05 ` [PATCH v8 11/11] proc: Move hidepid values to uapi as they are user interface to mount Alexey Gladkov
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