From: ebiederm@xmission.com (Eric W. Biederman)
To: LKML <linux-kernel@vger.kernel.org>
Cc: Oleg Nesterov <oleg@redhat.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
Thomas Gleixner <tglx@linutronix.de>
Subject: [PATCH v1 1/4] posix-cpu-timer: Tidy up group_leader logic in lookup_task
Date: Tue, 28 Apr 2020 16:45:16 -0500 [thread overview]
Message-ID: <87ftcn709f.fsf_-_@x220.int.ebiederm.org> (raw)
In-Reply-To: <87mu6v70in.fsf_-_@x220.int.ebiederm.org> (Eric W. Biederman's message of "Tue, 28 Apr 2020 16:39:44 -0500")
Replace has_group_leader_pid with thread_group_leader. Years ago Oleg
suggested changing thread_group_leader to has_group_leader_pid to handle
races. Looking at the code then and now I don't see how it ever helped.
Especially as then the code really did need to be the
thread_group_leader.
Today it doesn't make a difference if thread_group_leader races with
de_thread as the task returned from lookup_task in the non-thread case
is just used to find values in task->signal.
Since the races with de_thread have never been handled revert
has_group_header_pid to thread_group_leader for clarity.
Update the comment in lookup_task to remove implementation details that
are no longer true and to mention task->signal instead of task->sighand,
as the relevant cpu timer details are all in task->signal.
Ref: 55e8c8eb2c7b ("posix-cpu-timers: Store a reference to a pid not a task")
Ref: c0deae8c9587 ("posix-cpu-timers: Rcu_read_lock/unlock protect find_task_by_vpid call")
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
---
kernel/time/posix-cpu-timers.c | 8 ++------
1 file changed, 2 insertions(+), 6 deletions(-)
diff --git a/kernel/time/posix-cpu-timers.c b/kernel/time/posix-cpu-timers.c
index 2fd3b3fa68bf..e4051e417bcb 100644
--- a/kernel/time/posix-cpu-timers.c
+++ b/kernel/time/posix-cpu-timers.c
@@ -69,12 +69,8 @@ static struct task_struct *lookup_task(const pid_t pid, bool thread,
if (gettime) {
/*
* For clock_gettime(PROCESS) the task does not need to be
- * the actual group leader. tsk->sighand gives
+ * the actual group leader. task->signal gives
* access to the group's clock.
- *
- * Timers need the group leader because they take a
- * reference on it and store the task pointer until the
- * timer is destroyed.
*/
return (p == current || thread_group_leader(p)) ? p : NULL;
}
@@ -82,7 +78,7 @@ static struct task_struct *lookup_task(const pid_t pid, bool thread,
/*
* For processes require that p is group leader.
*/
- return has_group_leader_pid(p) ? p : NULL;
+ return thread_group_leader(p) ? p : NULL;
}
static struct task_struct *__get_task_for_clock(const clockid_t clock,
--
2.20.1
next prev parent reply other threads:[~2020-04-28 21:48 UTC|newest]
Thread overview: 54+ 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 ` [PATCH v4 0/2] proc: Ensure we see the exit of each process tid exactly Eric W. Biederman
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
2020-04-28 21:39 ` [PATCH v1 0/4] signal: Removing has_group_leader_pid Eric W. Biederman
2020-04-28 21:45 ` Eric W. Biederman [this message]
2020-04-28 21:48 ` [PATCH 2/4] posix-cpu-timer: Unify the now redundant code in lookup_task Eric W. Biederman
2020-04-28 21:53 ` [PATCH v1 3/4] exec: Remove BUG_ON(has_group_leader_pid) Eric W. Biederman
2020-04-28 21:56 ` [PATCH v4 4/4] signal: Remove has_group_leader_pid Eric W. Biederman
2020-04-30 11:54 ` [PATCH v1 0/3] posix-cpu-timers: Use pids not tasks in lookup Eric W. Biederman
2020-04-30 11:55 ` [PATCH v1 1/3] posix-cpu-timers: Extend rcu_read_lock removing task_struct references Eric W. Biederman
2020-04-30 11:56 ` [PATCH v1 2/3] posix-cpu-timers: Replace cpu_timer_pid_type with clock_pid_type Eric W. Biederman
2020-04-30 11:56 ` [PATCH v1 3/3] posix-cpu-timers: Replace __get_task_for_clock with pid_for_clock 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=87ftcn709f.fsf_-_@x220.int.ebiederm.org \
--to=ebiederm@xmission.com \
--cc=linux-kernel@vger.kernel.org \
--cc=oleg@redhat.com \
--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).