Hi Greg KH: We have a potential race on dereferencing tty->disc_data, so we should use some locks to avoid the competition. In the current version, it defines disc_data_lock to protect the race of ppp_asynctty_receive and ppp_asynctty_close. However, I think when cpu A is running ppp_asynctty_receive, another cpu B will not run ppp_asynctty_close at the same time. The reasons are as follows:
Cpu A will hold tty->ldisc_sem before running ppp_asynctty_receive. If cpu B wants to run ppp_asynctty_close, it must wait until cpu A release tty->ldisc_sem after ppp_asynctty_receive. So I think tty->ldisc_sem already can protect the tty->disc_data. About your question: What changed from v1? ==>just change some description. And how did you test this? Why remove this lock, is it causing problems somewhere for it to be here? ==>Somedays ago, There is a problem in n_tty line discipline. Specific description is here: https://lkml.org/lkml/2020/12/9/339 At the beginning I tried to add a lock in the layer of n_tty, until I find the patch https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?h=v5.9-rc4&id=83d817f41070c48bc3eb7ec18e43000a548fca5c About the patch, Specific description is here: https://lkml.org/lkml/2018/8/29/555 Thanks Gao Yan ----- Original mail ----- On Fri, Jan 01, 2021 at 11:37:18AM +0800, Gao Yan wrote: > In tty layer, it provides tty->ldisc_sem to protect all tty_ldisc_ops > including ppp_sync_ldisc. So I think tty->ldisc_sem can also protect > tty->disc_data, and the disc_data_lock is not necessary. > > Signed-off-by: Gao Yan <gao.y...@h3c.com> > --- > drivers/net/ppp/ppp_async.c | 11 ++--------- > drivers/net/ppp/ppp_synctty.c | 12 ++---------- > 2 files changed, 4 insertions(+), 19 deletions(-) What changed from v1? And how did you test this? Why remove this lock, is it causing problems somewhere for it to be here? thanks, greg k-h
