Re: [syzbot] possible deadlock in p9_write_work

[Dominique Martinet]

Tetsuo Handa wrote on Wed, Mar 30, 2022 at 07:35:47AM +0900:
> This seems to be an example of
> https://lkml.kernel.org/r/49925af7-78a8-a3dd-bce6-cfc02e1a9236@xxxxxxxxxxxxxxxxxxx
> introduced by "ext4: truncate during setxattr leads to kernel panic".

Thanks for the pointer

> Please don't use schedule_work() if you need to use flush_scheduled_work().

In this case we don't call flush_scheduled_work -- ext4 does.
The problem is mixing in the two subsystems when someone (e.g. syzbot)
opens an ext4 file and passes that fd to 9p when mounting with e.g.
mount -t 9p -o rfdno=<no>,wfdno=<no>

Frankly that's just not something I consider useful, interacting through
9p to a local file doesn't make sense except for testing.

If that is a real problem, the simplest way out would be to just forbid
non-socket FDs if it's something we can check.
-- 
Dominique