From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
To: oleg@redhat.com
Cc: dserrg@gmail.com, snanda@chromium.org, rientjes@google.com,
linux-kernel@vger.kernel.org
Subject: Question about replacing while_each_thread().
Date: Wed, 1 Feb 2017 19:47:32 +0900 [thread overview]
Message-ID: <201702011947.DBD56740.OMVHOLOtSJFFFQ@I-love.SAKURA.ne.jp> (raw)
Hello.
I have a question about commit 0c740d0afc3bff0a ("introduce
for_each_thread() to replace the buggy while_each_thread()").
IOPRIO_WHO_USER case in sys_ioprio_set()/sys_ioprio_get() in block/ioprio.c
are using
rcu_read_lock();
do_each_thread(g, p) {
(...snipped...)
} while_each_thread(g, p);
rcu_read_unlock();
sequence which is unsafe according to that commit, but
I'm not sure what the correct fix is.
That commit says
The new for_each_thread(g, t) helper is always safe under
rcu_read_lock() as long as this task_struct can't go away.
but what is the requirement for "can't go away" ?
Is rcu_read_lock() sufficient (i.e.
rcu_read_lock();
for_each_process_thread(g, p) {
(...snipped...)
}
rcu_read_unlock();
is OK) for "can't go away" ?
Is tasklist_lock held for read or write required (i.e.
read_lock(&tasklist_lock);
for_each_process_thread(g, p) {
(...snipped...)
}
read_unlock(&tasklist_lock);
is needed) for "can't go away" ?
I hope rcu_read_lock() is sufficient according to usage in
show_state_filter() and check_hung_uninterruptible_tasks().
Likewise, IOPRIO_WHO_PGRP case are using
rcu_read_lock();
do {
if ((pgrp) != NULL)
hlist_for_each_entry_rcu((p), &(pgrp)->tasks[PIDTYPE_PGID], pids[PIDTYPE_PGID].node) {
{
struct task_struct *tg___ = p;
do {
(...snipped...)
} while_each_thread(tg___, p);
p = tg___;
}
if (PIDTYPE_PGID == PIDTYPE_PID)
break;
}
} while (0);
rcu_read_unlock();
sequence which I guess it is unsafe as well.
In this case updating do_each_pid_thread() to use for_each_thread() and
updating while_each_pid_thread() not to use while_each_thread() is
the correct fix?
next reply other threads:[~2017-02-01 10:47 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-02-01 10:47 Tetsuo Handa [this message]
2017-02-01 17:19 ` Question about replacing while_each_thread() Oleg Nesterov
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=201702011947.DBD56740.OMVHOLOtSJFFFQ@I-love.SAKURA.ne.jp \
--to=penguin-kernel@i-love.sakura.ne.jp \
--cc=dserrg@gmail.com \
--cc=linux-kernel@vger.kernel.org \
--cc=oleg@redhat.com \
--cc=rientjes@google.com \
--cc=snanda@chromium.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).