BUG: debug_exception_enter() disables preemption and may call sleeping functions on aarch64 with RT

[Sebastian Andrzej Siewior]

On 2025-02-10 12:49:45 [+0000], Mark Rutland wrote:
> Hi,
Hi,

> I don't have an immediate suggestion; I'll need to go think about this
> for a bit. Unfortunatealy, there are several nested cans of worms here.
> :/
> 
> In theory, we can go split out the EL0 "debug exceptions" into separate
> handlers, and wouldn't generally need to disable preemption for things
> like BRK or single-step.
> 
> However, it's not immediately clear to me how we could handle
> watchpoints or breakpoints, since for those preemption/interruption
> could change the HW state under our feet, and we rely on single-step to
> skip past the watchpoint/breakpoint after it is handled.

Couldn't you delay sending signals until after the preempt-disable
section? 

> That, and last I looked reworking this we'd need to do a larger rework
> to split out those "debug exceptions" because of that way that currently
> bounces through the fault handling ligic in arch/arm64/mm/.
>
> Mark.

Sebastian