On Mon, 21 Sep 2026 11:54:36 +0200 David Woodhouse wrote: > On Mon, 2026-09-21 at 09:42 +0800, Hillf Danton wrote: > > On Sun, 20 Sep 2026 21:49:29 +0100 David Woodhouse wrote: > > > > > > Replace the per-cache rwlock with a dedicated per-VM atomic SRCU > > > domain (kvm->gpc_srcu) for the read side. Readers now run under > > > srcu_read_lock_atomic() alone — preemption disabled and non-blocking > > > enforced, which every GPC read-side section already satisfied as a > > > former rwlock critical section. It works in any context > > > (including hardirq and sched-out paths) and never fails or spins, > > > eliminating the > > > read_trylock() contortions in the atomic paths, the double-lock dance > > > with the lockdep subclass hack in the runstate update, and the > > > PREEMPT_RT problems inherent to taking an rwlock in those contexts. > > > In particular, kvm_xen_set_evtchn_fast() is called from hardirq > > > context (timer callback, kvm_arch_set_irq_inatomic()), where taking > > > gpc->lock is a sleeping-lock-in-atomic-context bug on PREEMPT_RT. > > > > Given the preempt_disable() in srcu_read_lock_atomic(), as PREEMPT_RT > > has no way of handling preempt_disable(), you need to add another > > version of srcu_read_lock_atomic() with preempt_disable() replaced with > > something like rcu_read_lock(). > > Hm? What's wrong with preempt_disable()? It works OK, but is generally
How is preempt_disable() handled by RT? > frowned upon in RT unless the sections are short and bounded of course. > Is this patchset going not to work with the preempt_disable() in srcu_read_lock_atomic() replaced with rcu_read_lock()?
