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SubjectRe: [PATCH] tty: add lockdep annotations
On Thu, 31 May 2012, Eric Dumazet wrote:

> From: Eric Dumazet <edumazet@google.com>
>
> tty_lock_pair() do the right thing to avoid deadlocks, but should
> instruct LOCKDEP of this to avoid a splat.

I have submitted very similar patch to Greg/Alan already 3 days ago[1],
but have been told that this is already fixed. Apparently it wasn't?

[1] https://lkml.org/lkml/2012/5/28/226

>
> Signed-off-by: Eric Dumazet <edumazet@google.com>
> ---
> Latest Linus tree still hang on my machine, at least this patch removes
> the lockdep problem...
>
> drivers/tty/tty_mutex.c | 19 +++++++++++++++----
> 1 file changed, 15 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/tty/tty_mutex.c b/drivers/tty/tty_mutex.c
> index 69adc80..67feac9 100644
> --- a/drivers/tty/tty_mutex.c
> +++ b/drivers/tty/tty_mutex.c
> @@ -6,11 +6,17 @@
>
> /* Legacy tty mutex glue */
>
> +enum {
> + TTY_MUTEX_NORMAL,
> + TTY_MUTEX_NESTED,
> +};
> +
> /*
> * Getting the big tty mutex.
> */
>
> -void __lockfunc tty_lock(struct tty_struct *tty)
> +static void __lockfunc tty_lock_nested(struct tty_struct *tty,
> + unsigned int subclass)
> {
> if (tty->magic != TTY_MAGIC) {
> printk(KERN_ERR "L Bad %p\n", tty);
> @@ -18,7 +24,12 @@ 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)
> +{
> + return tty_lock_nested(tty, TTY_MUTEX_NORMAL);
> }
> EXPORT_SYMBOL(tty_lock);
>
> @@ -43,11 +54,11 @@ void __lockfunc tty_lock_pair(struct tty_struct *tty,
> {
> if (tty < tty2) {
> tty_lock(tty);
> - tty_lock(tty2);
> + tty_lock_nested(tty2, TTY_MUTEX_NESTED);
> } else {
> if (tty2 && tty2 != tty)
> tty_lock(tty2);
> - tty_lock(tty);
> + tty_lock_nested(tty, TTY_MUTEX_NESTED);
> }
> }
> EXPORT_SYMBOL(tty_lock_pair);
>
>
> --
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>

--
Jiri Kosina
SUSE Labs



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