CVE-2025-21911: drm/imagination: avoid deadlock on fence release

In the Linux kernel, the following vulnerability has been resolved:

drm/imagination: avoid deadlock on fence release

Do scheduler queue fence release processing on a workqueue, rather than in the release function itself.

Fixes deadlock issues such as the following:

[ 607.400437] ============================================ [ 607.405755] WARNING: possible recursive locking detected [ 607.415500] -------------------------------------------- [ 607.420817] weston:zfq0/24149 is trying to acquire lock: [ 607.426131] ffff000017d041a0 (reservationwwclassmutex){+.+.}-{3:3}, at: pvrgemobjectvunmap+0x40/0xc0 [powervr] [ 607.436728] but task is already holding lock: [ 607.442554] ffff000017d105a0 (reservationwwclassmutex){+.+.}-{3:3}, at: dmabufioctl+0x250/0x554 [ 607.451727] other info that might help us debug this: [ 607.458245] Possible unsafe locking scenario:

[ 607.464155] CPU0 [ 607.466601] ---- [ 607.469044] lock(reservationwwclassmutex); [ 607.473584] lock(reservationwwclassmutex); [ 607.478114] DEADLOCK