After rebase to RHEL 8.4 binfmt_misc fs uses new fscontext API,
our implementation is incorrect. We have to use get_tree_keyed()
helper instead of get_tree_single() which allows only one
superblock per HN.
Fixes: 90fb0e274 ("ve/fs/binfmt: virtualization")
https://jira.sw.ru/browse/PSBM-132709
Currently some allocations can silently bypass accounting to root memcg.
This happen for __GFP_ACCOUNT allocations and if current task got fatal signal.
In vz8 and upstream this check was removed, and such allocations
are accounted to specified memcg without any limits.
I hope this helps to
