CVE-2026-90209

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CVE-2026-90209
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
debugfs_file_get()
debug_unregister()
mutex_lock(debug_mutex)
debugfs_remove()
wait for debugfs_file_put()
debug_file_ops.write()
debug_input()
mutex_lock(debug_mutex) ==> DEADLOCK

Fix this by splitting debug_unregister() into an s390dbf and debugfs
part, and running only the s390dbf part with debug_mutex locked.