Messages in this thread Patch in this message |  | | | Subject | Re: [PATCH] tty: tty_mutex: fix lockdep warning in tty_lock_pair | | From | Peter Zijlstra <> | | Date | Thu, 17 May 2012 20:48:38 +0200 |
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On Thu, 2012-05-17 at 11:28 -0700, Greg Kroah-Hartman wrote: > > +static void __lockfunc tty_lock_nest_lock(struct tty_struct *tty, > > + struct tty_struct *tty2) > > Duplicating tty_lock() just for this one issue seems wrong and prone to > error, don't you think? > > > +{ > > + if (tty->magic != TTY_MAGIC) { > > + printk(KERN_ERR "L Bad %p\n", tty); > > + WARN_ON(1); > > + return; > > + } > > + tty_kref_get(tty); > > + mutex_lock_nest_lock(&tty->legacy_mutex, &tty2->legacy_mutex);
Yeah, its completely broken, even the lockdep annotation is the wrong one.
Something like the (completely untested) below patch is the 'right' way.
--- drivers/tty/tty_mutex.c | 35 ++++++++++++++++++++--------------- 1 file changed, 20 insertions(+), 15 deletions(-) diff --git a/drivers/tty/tty_mutex.c b/drivers/tty/tty_mutex.c index 69adc80..587330b 100644 --- a/drivers/tty/tty_mutex.c +++ b/drivers/tty/tty_mutex.c @@ -10,7 +10,7 @@ * Getting the big tty mutex. */ -void __lockfunc tty_lock(struct tty_struct *tty) +static void __lockfunc tty_lock_nested(struct tty_struct *tty, int subclass) { if (tty->magic != TTY_MAGIC) { printk(KERN_ERR "L Bad %p\n", tty); @@ -18,7 +18,12 @@ void __lockfunc tty_lock(struct tty_struct *tty) return; } tty_kref_get(tty); - mutex_lock(&tty->legacy_mutex); + mutex_lock_nested(&tty->legacy_mutex, subclass); +} + +void __lockfunc tty_lock(struct tty_struct *tty) +{ + tty_lock_nested(tty, 0); } EXPORT_SYMBOL(tty_lock); @@ -38,25 +43,25 @@ EXPORT_SYMBOL(tty_unlock); * Getting the big tty mutex for a pair of ttys with lock ordering * On a non pty/tty pair tty2 can be NULL which is just fine. */ -void __lockfunc tty_lock_pair(struct tty_struct *tty, - struct tty_struct *tty2) +void __lockfunc tty_lock_pair(struct tty_struct *tty1, struct tty_struct *tty2) { - if (tty < tty2) { - tty_lock(tty); - tty_lock(tty2); - } else { - if (tty2 && tty2 != tty) - tty_lock(tty2); - tty_lock(tty); + if (!tty2 || tty1 == tty2) { + tty_lock(tty1); + return; } + + if (tty2 < tty1) + swap(tty1, tty2); + + tty_lock(tty1); + tty_lock_nested(tty2, SINGLE_DEPTH_NESTING); } EXPORT_SYMBOL(tty_lock_pair); -void __lockfunc tty_unlock_pair(struct tty_struct *tty, - struct tty_struct *tty2) +void __lockfunc tty_unlock_pair(struct tty_struct *tty1, struct tty_struct *tty2) { - tty_unlock(tty); - if (tty2 && tty2 != tty) + tty_unlock(tty1); + if (tty2 && tty2 != tty1) tty_unlock(tty2); } EXPORT_SYMBOL(tty_unlock_pair);
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