Messages in this thread | | | Date | Wed, 4 Oct 2023 10:40:43 +0200 | Subject | Re: [PATCH 1/1] tty: n_gsm: Avoid sleeping during .write() whilst atomic | From | Jiri Slaby <> |
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On 04. 10. 23, 8:05, Greg Kroah-Hartman wrote: > On Wed, Oct 04, 2023 at 05:59:09AM +0000, Starke, Daniel wrote: >>> Daniel, any thoughts? >> >> Our application of this protocol is only with specific modems to enable >> circuit switched operation (handling calls, selecting/querying networks, >> etc.) while doing packet switched communication (i.e. IP traffic over PPP). >> The protocol was developed for such use cases. >> >> Regarding the issue itself: >> There was already an attempt to fix all this by switching from spinlocks to >> mutexes resulting in ~20% performance loss. However, the patch was reverted >> as it did not handle the T1 timer leading into sleep during atomic within >> gsm_dlci_t1() on every mutex lock there. >> There was also a suggestion to fix this in do_con_write() as >> tty_operations::write() appears to be documented as "not allowed to sleep". >> The patch for this was rejected. It did not fix the issue within n_gsm. >> >> Link: https://lore.kernel.org/all/20221203215518.8150-1-pchelkin@ispras.ru/ >> Link: https://lore.kernel.org/all/20221212023530.2498025-1-zengheng4@huawei.com/ >> Link: https://lore.kernel.org/all/5a994a13-d1f2-87a8-09e4-a877e65ed166@kernel.org/ > > Ok, I thought I remembered this, I'll just drop this patch from my > review queue and wait for a better solution if it ever comes up as this > isn't a real issue that people are seeing on actual systems, but just a > syzbot report.
I remember too and it is not easy.
So without actually looking into the code, can we just somehow disallow attaching this line discipline to a console (ban such a TIOCSETD) and be done with this issue? IOW disallow root to shoot their foot.
regards, -- js suse labs
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