Re: [RFC PATCH] arm64/fpsimd: Don't disable softirq when touching FPSIMD/SVE state

[Sebastian Andrzej Siewior]

On 2019-04-05 10:02:45 [+0100], Julien Grall wrote:
> RT folks already saw this corruption because local_bh_disable() does not
> preempt on RT. They are carrying a patch (see "arm64: fpsimd: use
> preemp_disable in addition to local_bh_disable()") to disable preemption
> along with local_bh_disable().
> 
> Alternatively, Julia suggested to introduce a per-cpu lock to protect the
> state. I am thinking to defer this for a follow-up patch. The changes in
> this patch should make it easier because we now have helper to mark the
> critical section.

A per-CPU lock? It has to be a raw_spinlock_t because a normal
spin_lock() / local_lock() would allow scheduling and might be taken as
part of the context switch or soon after.

Sebastian