On Tue, Feb 10, 2026 at 11:46:44AM +0100, Christian König wrote: > On 2/10/26 11:36, Danilo Krummrich wrote: > > On Tue Feb 10, 2026 at 11:15 AM CET, Alice Ryhl wrote: > >> One way you can see this is by looking at what we require of the > >> workqueue. For all this to work, it's pretty important that we never > >> schedule anything on the workqueue that's not signalling safe, since > >> otherwise you could have a deadlock where the workqueue is executes some > >> random job calling kmalloc(GFP_KERNEL) and then blocks on our fence, > >> meaning that the VM_BIND job never gets scheduled since the workqueue > >> is never freed up. Deadlock. > > > > Yes, I also pointed this out multiple times in the past in the context of C > > GPU > > scheduler discussions. It really depends on the workqueue and how it is > > used. > > > > In the C GPU scheduler the driver can pass its own workqueue to the > > scheduler, > > which means that the driver has to ensure that at least one out of the > > wq->max_active works is free for the scheduler to make progress on the > > scheduler's run and free job work. > > > > Or in other words, there must be no more than wq->max_active - 1 works that > > execute code violating the DMA fence signalling rules.
Ouch, is that really the best way to do that? Why not two workqueues? > *And* the workqueue must be created with WQ_MEM_RECLAIM so that work > items can also start under memory pressure and not potentially cycle > back into the memory management to wait for a dma_fence to signal. > > But apart from that your explanation is perfectly correct, yes. Ah, interesting point. Alice
