From: ebiederm@xmission.com (Eric W. Biederman)
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: LKML <linux-kernel@vger.kernel.org>,
Linux FS Devel <linux-fsdevel@vger.kernel.org>,
Alexey Dobriyan <adobriyan@gmail.com>,
Alexey Gladkov <legion@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
Alexey Gladkov <gladkov.alexey@gmail.com>,
Oleg Nesterov <oleg@redhat.com>,
Thomas Gleixner <tglx@linutronix.de>,
"Paul E. McKenney" <paulmck@kernel.org>
Subject: [PATCH v4 0/2] proc: Ensure we see the exit of each process tid exactly
Date: Tue, 28 Apr 2020 07:16:44 -0500 [thread overview]
Message-ID: <87sggnajpv.fsf_-_@x220.int.ebiederm.org> (raw)
In-Reply-To: <CAHk-=wjSM9mgsDuX=ZTy2L+S7wGrxZMcBn054As_Jyv8FQvcvQ@mail.gmail.com> (Linus Torvalds's message of "Mon, 27 Apr 2020 13:27:40 -0700")
In the work to remove proc_mnt I noticed that we were calling
proc_flush_task now proc_flush_pid possibly multiple times for the same
pid because of how de_thread works.
This is a bare minimal patchset to sort out de_thread, by introducing
exchange_tids and the helper of exchange_tids hlists_swap_heads_rcu.
The actual call of exchange_tids should be slowpath so I have
prioritized readability over getting every last drop of performance.
I have also read through a bunch of the code to see if I could find
anything that would be affected by this change. Users of
has_group_leader_pid were a good canidates. But I also looked at other
cases that might have a pid->task->pid transition. I ignored other
sources of races with de_thread and exec as those are preexisting.
I found a close call with send_signals user of task_active_pid_ns, but
all pids of a thread group are guaranteeds to be in the same pid
namespace so there is not a problem.
I found a few pieces of debugging code that do:
task = pid_task(pid, PIDTYPE_PID);
if (task) {
printk("%u\n", task->pid);
}
But I can't see how we care if it happens at the wrong moment that
task->pid might not match pid_nr(pid);
Similarly because the code in posix-cpu-timers goes pid->task->pid it
feels like there should be a problem. But as the code that works with
PIDTYPE_PID is only available within the thread group, and as de_thread
kills all of the other threads before it makes any changes of this
kind the race can not happen.
In short I don't think this change will introduce any regressions.
Eric W. Biederman (2):
rculist: Add hlists_swap_heads_rcu
proc: Ensure we see the exit of each process tid exactly once
fs/exec.c | 5 +----
include/linux/pid.h | 1 +
include/linux/rculist.h | 21 +++++++++++++++++++++
kernel/pid.c | 19 +++++++++++++++++++
4 files changed, 42 insertions(+), 4 deletions(-)
Eric
next prev parent reply other threads:[~2020-04-28 12:20 UTC|newest]
Thread overview: 45+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-19 14:10 [PATCH v12 0/7] proc: modernize proc to support multiple private instances Alexey Gladkov
2020-04-19 14:10 ` [PATCH v12 1/7] proc: rename struct proc_fs_info to proc_fs_opts Alexey Gladkov
2020-04-19 14:10 ` [PATCH v12 2/7] proc: allow to mount many instances of proc in one pid namespace Alexey Gladkov
2020-04-23 11:28 ` [PATCH v13 " Alexey Gladkov
2020-04-23 12:16 ` Eric W. Biederman
2020-04-23 20:01 ` Alexey Gladkov
2020-04-19 14:10 ` [PATCH v12 3/7] proc: instantiate only pids that we can ptrace on 'hidepid=4' mount option Alexey Gladkov
2020-04-19 14:10 ` [PATCH v12 4/7] proc: add option to mount only a pids subset Alexey Gladkov
2020-04-19 14:10 ` [PATCH v12 5/7] docs: proc: add documentation for "hidepid=4" and "subset=pid" options and new mount behavior Alexey Gladkov
2020-04-19 14:10 ` [PATCH v12 6/7] proc: use human-readable values for hidepid Alexey Gladkov
2020-04-19 14:10 ` [PATCH v12 7/7] proc: use named enums for better readability Alexey Gladkov
[not found] ` <87ftcv1nqe.fsf@x220.int.ebiederm.org>
2020-04-23 17:54 ` [PATCH v2 0/2] proc: Calling proc_flush_task exactly once per task Oleg Nesterov
2020-04-23 19:38 ` Eric W. Biederman
2020-04-23 19:39 ` [PATCH v2 1/2] proc: Use PIDTYPE_TGID in next_tgid Eric W. Biederman
2020-04-24 17:29 ` Oleg Nesterov
2020-04-23 19:39 ` [PATCH v2 2/2] proc: Ensure we see the exit of each process tid exactly Eric W. Biederman
2020-04-23 20:28 ` Linus Torvalds
2020-04-24 3:33 ` Eric W. Biederman
2020-04-24 18:02 ` Linus Torvalds
2020-04-24 18:46 ` Linus Torvalds
2020-04-24 19:51 ` Eric W. Biederman
2020-04-24 20:10 ` Linus Torvalds
2020-04-24 17:39 ` Oleg Nesterov
2020-04-24 18:10 ` Eric W. Biederman
2020-04-24 20:50 ` [PATCH] proc: Put thread_pid in release_task not proc_flush_pid Eric W. Biederman
[not found] ` <87mu6ymkea.fsf_-_@x220.int.ebiederm.org>
[not found] ` <87blnemj5t.fsf_-_@x220.int.ebiederm.org>
2020-04-26 17:22 ` [PATCH v3 2/6] posix-cpu-timers: Use PIDTYPE_TGID to simplify the logic in lookup_task Oleg Nesterov
2020-04-27 11:51 ` Eric W. Biederman
2020-04-28 18:03 ` Oleg Nesterov
2020-04-27 10:32 ` Thomas Gleixner
2020-04-27 19:46 ` Eric W. Biederman
[not found] ` <875zdmmj4y.fsf_-_@x220.int.ebiederm.org>
2020-04-26 17:40 ` [PATCH v3 3/6] rculist: Add hlist_swap_before_rcu Linus Torvalds
2020-04-27 14:28 ` Eric W. Biederman
2020-04-27 20:27 ` Linus Torvalds
2020-04-28 12:16 ` Eric W. Biederman [this message]
2020-04-28 12:18 ` [PATCH v4 1/2] rculist: Add hlists_swap_heads_rcu Eric W. Biederman
2020-04-28 12:19 ` [PATCH v4 2/2] proc: Ensure we see the exit of each process tid exactly once Eric W. Biederman
2020-04-28 16:53 ` [PATCH v4 0/2] proc: Ensure we see the exit of each process tid exactly Linus Torvalds
2020-04-28 17:55 ` Eric W. Biederman
2020-04-28 18:55 ` Eric W. Biederman
2020-04-28 19:36 ` Linus Torvalds
2020-04-28 18:05 ` Oleg Nesterov
2020-04-28 18:54 ` Eric W. Biederman
[not found] ` <87h7x6mj6h.fsf_-_@x220.int.ebiederm.org>
2020-04-27 9:43 ` [PATCH v3 1/6] posix-cpu-timers: Always call __get_task_for_clock holding rcu_read_lock Thomas Gleixner
2020-04-27 11:53 ` Eric W. Biederman
[not found] ` <87r1w8ete7.fsf@x220.int.ebiederm.org>
2020-04-27 20:23 ` [PATCH v3] proc: Ensure we see the exit of each process tid exactly Eric W. Biederman
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=87sggnajpv.fsf_-_@x220.int.ebiederm.org \
--to=ebiederm@xmission.com \
--cc=adobriyan@gmail.com \
--cc=akpm@linux-foundation.org \
--cc=gladkov.alexey@gmail.com \
--cc=legion@kernel.org \
--cc=linux-fsdevel@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=oleg@redhat.com \
--cc=paulmck@kernel.org \
--cc=tglx@linutronix.de \
--cc=torvalds@linux-foundation.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).