From: Thomas Gleixner <tglx@linutronix.de>
To: "Eric W. Biederman" <ebiederm@xmission.com>,
LKML <linux-kernel@vger.kernel.org>
Cc: 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>,
Linus Torvalds <torvalds@linux-foundation.org>,
Oleg Nesterov <oleg@redhat.com>,
"Paul E. McKenney" <paulmck@kernel.org>
Subject: Re: [PATCH v3 2/6] posix-cpu-timers: Use PIDTYPE_TGID to simplify the logic in lookup_task
Date: Mon, 27 Apr 2020 12:32:21 +0200 [thread overview]
Message-ID: <87zhaxqkwa.fsf@nanos.tec.linutronix.de> (raw)
In-Reply-To: <87blnemj5t.fsf_-_@x220.int.ebiederm.org>
ebiederm@xmission.com (Eric W. Biederman) writes:
> Using pid_task(find_vpid(N), PIDTYPE_TGID) guarantees that if a task
> is found it is at that moment the thread group leader. Which removes
> the need for the follow on test has_group_leader_pid.
>
> I have reorganized the rest of the code in lookup_task for clarity,
> and created a common return for most of the code.
Sorry, it's way harder to read than the very explicit exits which were
there before.
> The special case for clock_gettime with "pid == gettid" is not my
> favorite. I strongly suspect it isn't used as gettid is such a pain,
> and passing 0 is much easier. Still it is easier to keep this special
> case than to do the reasarch that will show it isn't used.
It might be not your favorite, but when I refactored the code I learned
the hard way that one of the test suites has assumptions that
clock_gettime(PROCESS) works from any task of a group and not just for
the group leader. Sure we could fix the test suite, but test code tends
to be copied ...
> /*
> * Functions for validating access to tasks.
> */
> -static struct task_struct *lookup_task(const pid_t pid, bool thread,
> +static struct task_struct *lookup_task(const pid_t which_pid, bool thread,
> bool gettime)
> {
> struct task_struct *p;
> + struct pid *pid;
>
> /*
> * If the encoded PID is 0, then the timer is targeted at current
> * or the process to which current belongs.
> */
> - if (!pid)
> + if (!which_pid)
> return thread ? current : current->group_leader;
>
> - p = find_task_by_vpid(pid);
> - if (!p)
> - return p;
> -
> - if (thread)
> - return same_thread_group(p, current) ? p : NULL;
> -
> - if (gettime) {
> + pid = find_vpid(which_pid);
> + if (thread) {
> + p = pid_task(pid, PIDTYPE_PID);
> + if (p && !same_thread_group(p, current))
> + p = NULL;
> + } else {
> /*
> * For clock_gettime(PROCESS) the task does not need to be
> * the actual group leader. tsk->sighand gives
> @@ -76,13 +75,13 @@ static struct task_struct *lookup_task(const pid_t pid, bool thread,
> * reference on it and store the task pointer until the
> * timer is destroyed.
Btw, this comment is wrong since
55e8c8eb2c7b ("posix-cpu-timers: Store a reference to a pid not a task")
Thanks,
tglx
next prev parent reply other threads:[~2020-04-27 10:32 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 [this message]
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 ` [PATCH v1 1/4] posix-cpu-timer: Tidy up group_leader logic in lookup_task Eric W. Biederman
2020-04-28 21:48 ` [PATCH 2/4] posix-cpu-timer: Unify the now redundant code " 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
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