From: Linus Torvalds <torvalds@linux-foundation.org>
To: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>,
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>,
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>,
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 16:48:14 -0800 [thread overview]
Message-ID: <CAHk-=wgmn9Qds0VznyphouSZW6e42GWDT5H1dpZg8pyGDGN+=w@mail.gmail.com> (raw)
In-Reply-To: <87lfp7h422.fsf@x220.int.ebiederm.org>
On Wed, Feb 12, 2020 at 1:48 PM Eric W. Biederman <ebiederm@xmission.com> wrote:
>
> The good news is proc_flush_task isn't exactly called from process exit.
> proc_flush_task is called during zombie clean up. AKA release_task.
Yeah, that at least avoids some of the nasty locking while dying debug problems.
But the one I was more worried about was actually the lock contention
issue with lots of processes. The lock is basically a single global
lock in many situations - yes, it's technically per-ns, but in a lot
of cases you really only have one namespace anyway.
And we've had problems with global locks in this area before, notably
the one you call out:
> Further after proc_flush_task does it's thing the code goes
> and does "write_lock_irq(&task_list_lock);"
Yeah, so it's not introducing a new issue, but it is potentially
making something we already know is bad even worse.
> What would be downside of having a mutex for a list of proc superblocks?
> A mutex that is taken for both reading and writing the list.
That's what the original patch actually was, and I was hoping we could
avoid that thing.
An rwsem would be possibly better, since most cases by far are likely
about reading.
And yes, I'm very aware of the task_list_lock, but it's literally why
I don't want to make a new one.
I'm _hoping_ we can some day come up with something better than task_list_lock.
Linus
WARNING: multiple messages have this Message-ID (diff)
From: Linus Torvalds <torvalds-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>
To: "Eric W. Biederman" <ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org>
Cc: Al Viro <viro-RmSDqhL/yNMiFSDQTTA3OLVCufUGDwFn@public.gmane.org>,
LKML <linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
Kernel Hardening
<kernel-hardening-ZwoEplunGu1jrUoiu81ncdBPR1lH4CV8@public.gmane.org>,
Linux API <linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
Linux FS Devel
<linux-fsdevel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
Linux Security Module
<linux-security-module-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
Akinobu Mita
<akinobu.mita-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>,
Alexey Dobriyan
<adobriyan-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>,
Andrew Morton
<akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>,
Andy Lutomirski <luto-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>,
Daniel Micay
<danielmicay-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>,
Djalal Harouni <tixxdz-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>,
"Dmitry V . Levin" <ldv-u2l5PoMzF/Vg9hUCZPvPmw@public.gmane.org>,
Greg Kroah-Hartman
<gregkh-hQyY1W1yCW8ekmWlsbkhG0B+6BGkLq7r@public.gmane.org>,
Ingo Molnar <mingo-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>,
"J . Bruce Fields"
<bfields-uC3wQj2KruNg9hUCZPvPmw@public.gmane.org>,
Jeff Layton <jlayton-vpEMnDpepFuMZCB2o+C8xQ@public.gmane.org>,
Jonathan Corbet <corbet-T1hC0tSOHrs@public.gmane.org>,
Kees
Subject: Re: [PATCH v8 07/11] proc: flush task dcache entries from all procfs instances
Date: Wed, 12 Feb 2020 16:48:14 -0800 [thread overview]
Message-ID: <CAHk-=wgmn9Qds0VznyphouSZW6e42GWDT5H1dpZg8pyGDGN+=w@mail.gmail.com> (raw)
In-Reply-To: <87lfp7h422.fsf-JOvCrm2gF+uungPnsOpG7nhyD016LWXt@public.gmane.org>
On Wed, Feb 12, 2020 at 1:48 PM Eric W. Biederman <ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org> wrote:
>
> The good news is proc_flush_task isn't exactly called from process exit.
> proc_flush_task is called during zombie clean up. AKA release_task.
Yeah, that at least avoids some of the nasty locking while dying debug problems.
But the one I was more worried about was actually the lock contention
issue with lots of processes. The lock is basically a single global
lock in many situations - yes, it's technically per-ns, but in a lot
of cases you really only have one namespace anyway.
And we've had problems with global locks in this area before, notably
the one you call out:
> Further after proc_flush_task does it's thing the code goes
> and does "write_lock_irq(&task_list_lock);"
Yeah, so it's not introducing a new issue, but it is potentially
making something we already know is bad even worse.
> What would be downside of having a mutex for a list of proc superblocks?
> A mutex that is taken for both reading and writing the list.
That's what the original patch actually was, and I was hoping we could
avoid that thing.
An rwsem would be possibly better, since most cases by far are likely
about reading.
And yes, I'm very aware of the task_list_lock, but it's literally why
I don't want to make a new one.
I'm _hoping_ we can some day come up with something better than task_list_lock.
Linus
next prev parent reply other threads:[~2020-02-13 0:54 UTC|newest]
Thread overview: 176+ 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 ` 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 15:05 ` Alexey Gladkov
2020-02-10 18:23 ` Andy Lutomirski
2020-02-10 18:23 ` Andy Lutomirski
2020-02-10 18:23 ` Andy Lutomirski
2020-02-12 15:00 ` Alexey Gladkov
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 ` 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
2020-02-10 18:30 ` Andy Lutomirski
2020-02-10 18:30 ` Andy Lutomirski
2020-02-12 14:57 ` Alexey Gladkov
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 ` 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 17:46 ` Linus Torvalds
2020-02-10 17:46 ` Linus Torvalds
2020-02-10 19:23 ` Al Viro
2020-02-10 19:23 ` Al Viro
2020-02-11 1:36 ` Eric W. Biederman
2020-02-11 1:36 ` Eric W. Biederman
2020-02-11 1:36 ` Eric W. Biederman
2020-02-11 4:01 ` Eric W. Biederman
2020-02-11 4:01 ` Eric W. Biederman
2020-02-11 4:01 ` Eric W. Biederman
2020-02-12 14:49 ` Alexey Gladkov
2020-02-12 14:49 ` Alexey Gladkov
2020-02-12 14:59 ` Eric W. Biederman
2020-02-12 14:59 ` Eric W. Biederman
2020-02-12 14:59 ` Eric W. Biederman
2020-02-12 17:08 ` Alexey Gladkov
2020-02-12 17:08 ` Alexey Gladkov
2020-02-12 18:45 ` Linus Torvalds
2020-02-12 18:45 ` Linus Torvalds
2020-02-12 18:45 ` Linus Torvalds
2020-02-12 19:16 ` Eric W. Biederman
2020-02-12 19:16 ` Eric W. Biederman
2020-02-12 19:16 ` Eric W. Biederman
2020-02-12 19:49 ` Linus Torvalds
2020-02-12 19:49 ` Linus Torvalds
2020-02-12 19:49 ` Linus Torvalds
2020-02-12 20:03 ` Al Viro
2020-02-12 20:03 ` Al Viro
2020-02-12 20:35 ` Linus Torvalds
2020-02-12 20:35 ` Linus Torvalds
2020-02-12 20:35 ` Linus Torvalds
2020-02-12 20:38 ` Al Viro
2020-02-12 20:38 ` Al Viro
2020-02-12 20:41 ` Al Viro
2020-02-12 20:41 ` Al Viro
2020-02-12 21:02 ` Linus Torvalds
2020-02-12 21:02 ` Linus Torvalds
2020-02-12 21:02 ` Linus Torvalds
2020-02-12 21:46 ` Eric W. Biederman
2020-02-12 21:46 ` Eric W. Biederman
2020-02-12 21:46 ` Eric W. Biederman
2020-02-13 0:48 ` Linus Torvalds [this message]
2020-02-13 0:48 ` Linus Torvalds
2020-02-13 0:48 ` Linus Torvalds
2020-02-13 4:37 ` Eric W. Biederman
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 21:30 ` Linus Torvalds
2020-02-13 22:23 ` Al Viro
2020-02-13 22:47 ` Linus Torvalds
2020-02-13 22:47 ` Linus Torvalds
2020-02-14 14:15 ` Eric W. Biederman
2020-02-14 14:15 ` Eric W. Biederman
2020-02-14 3:48 ` 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 20:46 ` 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 20:47 ` 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 20:48 ` 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 20:49 ` Eric W. Biederman
2020-02-20 22:33 ` Linus Torvalds
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 20:49 ` Eric W. Biederman
2020-02-20 22:43 ` Linus Torvalds
2020-02-20 22:43 ` Linus Torvalds
2020-02-20 22:54 ` Al Viro
2020-02-20 23:00 ` Linus Torvalds
2020-02-20 23:00 ` Linus Torvalds
2020-02-20 23:03 ` Al Viro
2020-02-20 23:39 ` Eric W. Biederman
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 20:51 ` 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 ` 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
2020-02-20 20:52 ` Eric W. Biederman
2020-02-21 16:50 ` Oleg Nesterov
2020-02-22 15:46 ` Eric W. Biederman
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 23:02 ` Linus Torvalds
2020-02-20 23:07 ` Al Viro
2020-02-20 23:37 ` Eric W. Biederman
2020-02-20 23:37 ` Eric W. Biederman
2020-02-24 16:25 ` [PATCH v2 0/6] " Eric W. Biederman
2020-02-24 16:25 ` 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 16:26 ` 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 ` 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 16:27 ` 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 ` 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 16:28 ` 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
2020-02-24 16:29 ` Eric W. Biederman
2020-02-28 20:17 ` [PATCH 0/3] proc: Actually honor the mount options Eric W. Biederman
2020-02-28 20:17 ` 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 ` 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 20:18 ` Eric W. Biederman
2020-02-28 20:30 ` Christian Brauner
2020-02-28 21:28 ` Eric W. Biederman
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 20:19 ` Eric W. Biederman
2020-02-28 20:39 ` Christian Brauner
2020-02-28 21:40 ` Eric W. Biederman
2020-02-28 21:40 ` Eric W. Biederman
2020-02-29 3:25 ` kbuild test robot
2020-02-29 3:25 ` kbuild test robot
2020-02-29 4:49 ` Eric W. Biederman
2020-02-29 4:49 ` Eric W. Biederman
2020-03-02 23:01 ` [kbuild-all] " Philip Li
2020-03-02 23:01 ` Philip Li
2020-03-12 2:03 ` [kbuild-all] " Li Zhijian
2020-03-12 2:03 ` Li Zhijian
2020-02-29 4:23 ` kbuild test robot
2020-02-29 4:23 ` kbuild test robot
2020-02-28 22:34 ` [PATCH 4/3] pid: Improve the comment about waiting in zap_pid_ns_processes Eric W. Biederman
2020-02-28 22:34 ` 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
2020-02-14 3:49 ` Eric W. Biederman
2020-02-12 19:47 ` Al Viro
2020-02-12 19:47 ` Al Viro
2020-02-11 22:45 ` Al Viro
2020-02-11 22:45 ` Al Viro
2020-02-12 14:26 ` Alexey Gladkov
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
2020-02-10 16:29 ` Jordan Glover
2020-02-12 14:34 ` Alexey Gladkov
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
2020-02-10 18:29 ` Andy Lutomirski
2020-02-10 18:29 ` Andy Lutomirski
2020-02-12 16:03 ` Alexey Gladkov
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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