Executive brief
In the Linux kernel, the following vulnerability has been resolved:
gfs2: fix quota init duplicate scan
gfs2_quota_init() checks for duplicate quota_change IDs while holding qd_lock and the quota hash bucket bitlock. That path used gfs2_qd_search_bucket(), which takes a lockref reference via lockref_get_not_dead().
On PREEMPT_RT this may sleep, which is not allowed under the bucket bitlock, triggering "sleeping function called from invalid context".
Use a no-ref bucket lookup in this path, then continue duplicate handling without taking a lockref there.
Refactor gfs2_qd_search_bucket() to build on top of the no-ref helper so lookup traversal stays in one place.
This patch fixes a bug reported by syzbot.