487df8b698
The Mesa issue referenced below pointed out a possible deadlock:
[ 1231.611031] Possible interrupt unsafe locking scenario:
[ 1231.611033] CPU0 CPU1
[ 1231.611034] ---- ----
[ 1231.611035] lock(&xa->xa_lock#17);
[ 1231.611038] local_irq_disable();
[ 1231.611039] lock(&fence->lock);
[ 1231.611041] lock(&xa->xa_lock#17);
[ 1231.611044] <Interrupt>
[ 1231.611045] lock(&fence->lock);
[ 1231.611047]
*** DEADLOCK ***
In this example, CPU0 would be any function accessing job->dependencies
through the xa_* functions that don't disable interrupts (eg:
drm_sched_job_add_dependency(), drm_sched_entity_kill_jobs_cb()).
CPU1 is executing drm_sched_entity_kill_jobs_cb() as a fence signalling
callback so in an interrupt context. It will deadlock when trying to
grab the xa_lock which is already held by CPU0.
Replacing all xa_* usage by their xa_*_irq counterparts would fix
this issue, but Christian pointed out another issue: dma_fence_signal
takes fence.lock and so does dma_fence_add_callback.
dma_fence_signal() // locks f1.lock
-> drm_sched_entity_kill_jobs_cb()
-> foreach dependencies
-> dma_fence_add_callback() // locks f2.lock
This will deadlock if f1 and f2 share the same spinlock.
To fix both issues, the code iterating on dependencies and re-arming them
is moved out to drm_sched_entity_kill_jobs_work().
Cc: stable@vger.kernel.org # v6.2+
Fixes:
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|---|---|---|
| .. | ||
| tests | ||
| .kunitconfig | ||
| Makefile | ||
| gpu_scheduler_trace.h | ||
| sched_entity.c | ||
| sched_fence.c | ||
| sched_internal.h | ||
| sched_main.c | ||