CVE-2026-90209: s390/debug: Fix deadlock during unregister
In the Linux kernel, the following vulnerability has been resolved:
s390/debug: Fix deadlock during unregister
Unregistering an s390dbf debug area while one of the associated debugfs files is being written to can cause a deadlock:
$ echo >.../vmur/level $ rmmod vmur =================================================== debugfs write debugfsfileget() debugunregister() mutexlock(debugmutex) debugfsremove() wait for debugfsfileput() debugfileops.write() debuginput() mutexlock(debugmutex) ==> DEADLOCK
Fix this by splitting debugunregister() into an s390dbf and debugfs part, and running only the s390dbf part with debugmutex locked.
Affected Software
Event History
Frequently Asked Questions
What conditions are required to trigger the deadlock?
An s390dbf debug area must be unregistered while a write to one of its associated debugfs files is in progress. The documented example is writing to vmur/level while the vmur module is removed.
What is the observable impact if the issue is triggered?
The unregister path and the debugfs write path can wait on each other indefinitely. This results in a deadlock during module removal or other debug-area unregister activity.
Are affected Linux kernel versions identified?
No affected version ranges are provided. The supplied references point to three stable kernel commits containing the resolution.