On 2020-10-27 11:09:51 [+0100], Thomas Gleixner wrote:
> --- a/arch/x86/include/asm/fpu/api.h
> +++ b/arch/x86/include/asm/fpu/api.h
> @@ -32,15 +32,27 @@ extern void fpregs_mark_activate(void);
> *
> * local_bh_disable() protects against both preemption and soft interrupts
> * on !RT kernels.
> + *
> + * On RT kernels local_bh_disable() is not sufficient because it only
> + * serializes soft interrupt related sections via a local lock, but stays
> + * preemptible. Disabling preemption is the right choice here as bottom
> + * half processing is always in thread context on RT kernels so it
> + * implicitly prevents bottom half processing as well.
The important part is that kernel_fpu_begin() also disables preemption
and it may run in softirq. It does not use fpregs_lock() and
fpregs_lock() serializes against kernel_fpu_begin().
> */
> static inline void fpregs_lock(void)
> {
> - local_bh_disable();
> + if (!IS_ENABLED(CONFIG_PREEMPT_RT))
> + local_bh_disable();
> + else
> + preempt_disable();
Could you please swap that to
if (IS_ENABLED(CONFIG_PREEMPT_RT))
preempt_disable();
else
local_bh_disable();
> }
>
Sebastian
