On Wed, Jun 16, 2021 at 11:23:34AM -0400, Tejun Heo wrote:
On Wed, Jun 16, 2021 at 08:51:57AM -0400, Paul Gortmaker wrote:
A fix would be to not leave the stale reference in fc->root as follows:
dput(fc->root);
fc->root = NULL;
deactivate_locked_super(sb);
...but then we are just open-coding a duplicate of fc_drop_locked() so we simply use that instead.
As this is unlikely to be a real-world problem both in probability and circumstances, I'm applying this to cgroup/for-5.14 instead of cgroup/for-5.13-fixes.
FWIW at Arm we've started seeing what appears to be this issue blow up very frequently in some of our internal LTP CI runs against -next, seems to be mostly on lower end platforms. We seem to have started finding it at roughly the same time that the Yocto people did, I guess some other change made it more likely to trigger. Not exactly real world usage obviously but it's creating quite a bit of noise in testing which is disruptive so it'd be good to get it into -next as a fix.