Messages in this thread Patch in this message | | | Date | Mon, 11 Jul 2005 14:33:37 -0400 (EDT) | From | Jason Baron <> | Subject | pty_chars_in_buffer oops fix |
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hi,
This is a re-posting of a fix for a race condition between changing the line discipline on a pty and and a poll on the 'other' side. The reference is: http://marc.theaimsgroup.com/?l=linux-kernel&m=111342171410005&w=2. Below is a diff against the current tree.
thanks,
-Jason
--- linux-2.6.12/drivers/char/pty.c 2005-06-17 15:48:29.000000000 -0400 +++ linux-2.6.12.working/drivers/char/pty.c 2005-07-11 12:21:03.000000000 -0400 @@ -149,15 +149,14 @@ static int pty_chars_in_buffer(struct tty_struct *tty) { struct tty_struct *to = tty->link; - ssize_t (*chars_in_buffer)(struct tty_struct *); int count; /* We should get the line discipline lock for "tty->link" */ - if (!to || !(chars_in_buffer = to->ldisc.chars_in_buffer)) + if (!to || !to->ldisc.chars_in_buffer) return 0; /* The ldisc must report 0 if no characters available to be read */ - count = chars_in_buffer(to); + count = to->ldisc.chars_in_buffer(to); if (tty->driver->subtype == PTY_TYPE_SLAVE) return count; --- linux-2.6.12/drivers/char/tty_io.c 2005-07-11 12:13:48.000000000 -0400 +++ linux-2.6.12.working/drivers/char/tty_io.c 2005-07-11 12:19:21.000000000 -0400 @@ -470,21 +470,19 @@ static int tty_set_ldisc(struct tty_struct *tty, int ldisc) { - int retval = 0; - struct tty_ldisc o_ldisc; + int retval = 0; + struct tty_ldisc o_ldisc; char buf[64]; int work; unsigned long flags; struct tty_ldisc *ld; + struct tty_struct *o_tty; if ((ldisc < N_TTY) || (ldisc >= NR_LDISCS)) return -EINVAL; restart: - if (tty->ldisc.num == ldisc) - return 0; /* We are already in the desired discipline */ - ld = tty_ldisc_get(ldisc); /* Eduardo Blanco <ejbs@cs.cs.com.uy> */ /* Cyrus Durgin <cider@speakeasy.org> */ @@ -495,45 +493,74 @@ if (ld == NULL) return -EINVAL; - o_ldisc = tty->ldisc; - tty_wait_until_sent(tty, 0); + if (tty->ldisc.num == ldisc) { + tty_ldisc_put(ldisc); + return 0; + } + + o_ldisc = tty->ldisc; + o_tty = tty->link; + /* * Make sure we don't change while someone holds a * reference to the line discipline. The TTY_LDISC bit * prevents anyone taking a reference once it is clear. * We need the lock to avoid racing reference takers. */ - + spin_lock_irqsave(&tty_ldisc_lock, flags); - if(tty->ldisc.refcount) - { - /* Free the new ldisc we grabbed. Must drop the lock - first. */ + if (tty->ldisc.refcount || (o_tty && o_tty->ldisc.refcount)) { + if(tty->ldisc.refcount) { + /* Free the new ldisc we grabbed. Must drop the lock + first. */ + spin_unlock_irqrestore(&tty_ldisc_lock, flags); + tty_ldisc_put(ldisc); + /* + * There are several reasons we may be busy, including + * random momentary I/O traffic. We must therefore + * retry. We could distinguish between blocking ops + * and retries if we made tty_ldisc_wait() smarter. That + * is up for discussion. + */ + if (wait_event_interruptible(tty_ldisc_wait, tty->ldisc.refcount == 0) < 0) + return -ERESTARTSYS; + goto restart; + } + if(o_tty && o_tty->ldisc.refcount) { + spin_unlock_irqrestore(&tty_ldisc_lock, flags); + tty_ldisc_put(ldisc); + if (wait_event_interruptible(tty_ldisc_wait, o_tty->ldisc.refcount == 0) < 0) + return -ERESTARTSYS; + goto restart; + } + } + + /* if the TTY_LDISC bit is set, then we are racing against another ldisc change */ + + if (!test_bit(TTY_LDISC, &tty->flags)) { spin_unlock_irqrestore(&tty_ldisc_lock, flags); tty_ldisc_put(ldisc); - /* - * There are several reasons we may be busy, including - * random momentary I/O traffic. We must therefore - * retry. We could distinguish between blocking ops - * and retries if we made tty_ldisc_wait() smarter. That - * is up for discussion. - */ - if(wait_event_interruptible(tty_ldisc_wait, tty->ldisc.refcount == 0) < 0) - return -ERESTARTSYS; + ld = tty_ldisc_ref_wait(tty); + tty_ldisc_deref(ld); goto restart; } - clear_bit(TTY_LDISC, &tty->flags); + + clear_bit(TTY_LDISC, &tty->flags); clear_bit(TTY_DONT_FLIP, &tty->flags); - spin_unlock_irqrestore(&tty_ldisc_lock, flags); - + if (o_tty) { + clear_bit(TTY_LDISC, &o_tty->flags); + clear_bit(TTY_DONT_FLIP, &o_tty->flags); + } + spin_unlock_irqrestore(&tty_ldisc_lock, flags); + /* * From this point on we know nobody has an ldisc * usage reference, nor can they obtain one until * we say so later on. */ - + work = cancel_delayed_work(&tty->flip.work); /* * Wait for ->hangup_work and ->flip.work handlers to terminate @@ -584,10 +611,12 @@ */ tty_ldisc_enable(tty); + if (o_tty) + tty_ldisc_enable(o_tty); /* Restart it in case no characters kick it off. Safe if already running */ - if(work) + if (work) schedule_delayed_work(&tty->flip.work, 1); return retval; } - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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