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SubjectRe: [PATCH 1/1] tty: disassociate_ctty() sends the extra SIGCONT
On 09/21, Peter Hurley wrote:
>
> On 09/21/2013 02:34 PM, Oleg Nesterov wrote:
>>
>> do_each_pid_task(tty->session, PIDTYPE_SID, p) {
>> spin_lock_irq(&p->sighand->siglock);
>> if (p->signal->tty == tty) {
>> p->signal->tty = NULL;
>> /* We defer the dereferences outside fo
>> the tasklist lock */
>> refs++;
>> }
>> if (!p->signal->leader) {
>> spin_unlock_irq(&p->sighand->siglock);
>> continue;
>> }
>> __group_send_sig_info(SIGHUP, SEND_SIG_PRIV, p);
>> __group_send_sig_info(SIGCONT, SEND_SIG_PRIV, p);
>> put_pid(p->signal->tty_old_pgrp); /* A noop */
>> spin_lock(&tty->ctrl_lock);
>> tty_pgrp = get_pid(tty->pgrp);
>>
>> I guess this can happen only once, so we could even add WARN_ON(tty_pgrp)
>> before get_pid(). But this look confusing, as if we can do get_pid()
>> multiple times and leak tty->pgrp.
>>
>> if (tty->pgrp)
>> p->signal->tty_old_pgrp = get_pid(tty->pgrp);
>>
>> else? We already did put_pid(tty_old_pgrp), we should clear it.
>>
>> IOW, do you think the patch below makes sense or I missed something?
>> Just curious.
>
> The code block you're referring to only executes once because there is
> only one session leader.

I understand, and I even mentioned this above.

My point was, this _looks_ confusing, and the patch I sent makes it
more clean.

And what about ->tty_old_pgrp? I still think that at least the patch
below makes sense. If tty->pgrp == NULL is not possible here (I do
not know), then why do we check? Otherwise ->tty_old_pgrp != NULL looks
certainly wrong after put_pid().

Oleg.

--- x/drivers/tty/tty_io.c
+++ x/drivers/tty/tty_io.c
@@ -569,8 +569,7 @@ static int tty_signal_session_leader(str
put_pid(p->signal->tty_old_pgrp); /* A noop */
spin_lock(&tty->ctrl_lock);
tty_pgrp = get_pid(tty->pgrp);
- if (tty->pgrp)
- p->signal->tty_old_pgrp = get_pid(tty->pgrp);
+ p->signal->tty_old_pgrp = get_pid(tty->pgrp);
spin_unlock(&tty->ctrl_lock);
spin_unlock_irq(&p->sighand->siglock);
} while_each_pid_task(tty->session, PIDTYPE_SID, p);


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