drm/vc4: Fix binner slot allocation failing on an idle GPU

A job's binner slots are returned to bin_alloc_used by vc4_complete_exec(),
which runs from the job_done workqueue, but the seqno
vc4_v3d_get_bin_slot() waits on is incremented earlier, in the function
vc4_irq_finish_render_job(). Therefore, a waiter can wake, retry, and still
find the pool full because the worker has not run. By then, the job might
have left the render_job_list, so no seqno remains to wait on and the
allocation fails returning -ENOMEM.

This scenario can be reproduced on a Raspberry Pi 3 by using a burst of
small jobs (e.g. Piglit's `quick_gl` suite), with userspace seeing a
rejected submit for a pool about to become free.

Note that the slots are held from validation until the render completes,
so the pool can also be exhausted by jobs still queued on bin_job_list,
leaving render_job_list empty and nothing to wait on.

Release the slots from the FRDONE handler and wait on the pool instead of
on one job's seqno. This bounds the wait to the actual resource. Also, by
claiming the slot inside the wait condition, another submit is unable to
take the slot between the wakeup and the retry. vc4_complete_exec() keeps
clearing the slots for jobs that never completed, and now wakes the
waiters too.

Note that the wait takes a deadline, since the two callers need different
ones. The submit path is a user task and can be interrupted, so it waits
without one. On the other hand, vc4_overflow_mem_work() runs on a worker
and never sees a signal, so it needs a deadline. During a reset,
vc4_irq_disable() masks V3D_DRIVER_IRQS before draining the worker, and
with those masked nothing can release a slot. This deadlocks: the worker
would wait for slots that only the reset can free, while the reset waits
in cancel_work_sync() for the worker.

Fixes: 553c942f8b2c ("drm/vc4: Allow using more than 256MB of CMA memory.")
Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>
Link: https://patch.msgid.link/20260930182204.1877361-1-mcanal@igalia.com
Signed-off-by: Maíra Canal <mcanal@igalia.com>

0 files changed, 0 insertions, 0 deletions