From: Peter Zijlstra <a.p.zijlstra@chello.nl>
To: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Andrew Morton <akpm@osdl.org>, Alan Cox <alan@redhat.com>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] do_task_stat: don't take tty_mutex
Date: Mon, 23 Oct 2006 13:16:41 +0200 [thread overview]
Message-ID: <1161602202.5230.91.camel@lappy> (raw)
In-Reply-To: <20061022155735.GA10491@oleg>
On Sun, 2006-10-22 at 19:57 +0400, Oleg Nesterov wrote:
> Depends on
> tty-signal-tty-locking.patch
>
> ->signal->tty is protected by ->siglock, no need to take the global tty_mutex.
>
> Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
->siglock protects the value of ->signal->tty, not memory it points to;
however since destroying the tty also means clearing all ->signal->tty
references, which means taking all ->siglocks, just holding the
->siglock around this piece of code looks sufficient indeed.
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
> --- rc2-mm2/fs/proc/array.c~ 2006-10-22 19:28:17.000000000 +0400
> +++ rc2-mm2/fs/proc/array.c 2006-10-22 19:45:52.000000000 +0400
> @@ -346,20 +346,13 @@ static int do_task_stat(struct task_stru
> sigemptyset(&sigcatch);
> cutime = cstime = utime = stime = cputime_zero;
>
> - mutex_lock(&tty_mutex);
> rcu_read_lock();
> if (lock_task_sighand(task, &flags)) {
> struct signal_struct *sig = task->signal;
> - struct tty_struct *tty = sig->tty;
>
> - if (tty) {
> - /*
> - * sig->tty is not stable, but tty_mutex
> - * protects us from release_dev(tty)
> - */
> - barrier();
> - tty_pgrp = tty->pgrp;
> - tty_nr = new_encode_dev(tty_devnum(tty));
> + if (sig->tty) {
> + tty_pgrp = sig->tty->pgrp;
> + tty_nr = new_encode_dev(tty_devnum(sig->tty));
> }
>
> num_threads = atomic_read(&sig->count);
> @@ -395,7 +388,6 @@ static int do_task_stat(struct task_stru
> unlock_task_sighand(task, &flags);
> }
> rcu_read_unlock();
> - mutex_unlock(&tty_mutex);
>
> if (!whole || num_threads<2)
> wchan = get_wchan(task);
>
next prev parent reply other threads:[~2006-10-23 11:16 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-10-22 15:57 [PATCH] do_task_stat: don't take tty_mutex Oleg Nesterov
2006-10-23 11:16 ` Peter Zijlstra [this message]
2006-10-23 14:05 ` 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=1161602202.5230.91.camel@lappy \
--to=a.p.zijlstra@chello.nl \
--cc=akpm@osdl.org \
--cc=alan@redhat.com \
--cc=linux-kernel@vger.kernel.org \
--cc=oleg@tv-sign.ru \
/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