Messages in this thread | | | Date | Thu, 9 May 2024 08:41:18 +0200 | Subject | Re: [PATCH] tty: Fix possible deadlock in tty_buffer_flush | From | Jiri Slaby <> |
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On 08. 05. 24, 11:30, kovalev@altlinux.org wrote: > From: Vasiliy Kovalev <kovalev@altlinux.org> > > A possible scenario in which a deadlock may occur is as follows: > > flush_to_ldisc() { > > mutex_lock(&buf->lock); > > tty_port_default_receive_buf() { > tty_ldisc_receive_buf() { > n_tty_receive_buf2() { > n_tty_receive_buf_common() { > n_tty_receive_char_special() { > isig() { > tty_driver_flush_buffer() { > pty_flush_buffer() { > tty_buffer_flush() { > > mutex_lock(&buf->lock); (DEADLOCK) > > flush_to_ldisc() and tty_buffer_flush() functions they use the same mutex > (&buf->lock), but not necessarily the same struct tty_bufhead object.
"not necessarily" -- so does it mean that it actually can happen (and we should fix it) or not at all (and we should annotate the mutex)?
> However, you should probably use a separate mutex for the > tty_buffer_flush() function to exclude such a situation. ..
> Cc: stable@vger.kernel.org
What commit does this fix?
> --- a/drivers/tty/tty_buffer.c > +++ b/drivers/tty/tty_buffer.c > @@ -226,7 +226,7 @@ void tty_buffer_flush(struct tty_struct *tty, struct tty_ldisc *ld) > > atomic_inc(&buf->priority); > > - mutex_lock(&buf->lock); > + mutex_lock(&buf->flush_mtx);
Hmm, how does this protect against concurrent buf pickup. We free it here and the racing thread can start using it, or?
> /* paired w/ release in __tty_buffer_request_room; ensures there are > * no pending memory accesses to the freed buffer > */
thanks, -- js suse labs
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