Re: [PATCH 2/2] perf/hw_breakpoint: Modify breakpoint even if the new attr has disabled set

[Oleg Nesterov]

On 08/06, Oleg Nesterov wrote:
>
> But, with or without this fix, shouldn't we set .disabled = 1 if modify_() fails?
> IIUC this doesn't matter, bp->attr.disabled is not really used anyway, but looks a
> bit confusing.

I am looking at another caller perf_event_modify_breakpoint(). It too doesn't set
attr.disabled = 1 on failure, it does _perf_event_enable() instead so attr.disabled
should be correct.

But this looks wrong. If modify_user_hw_breakpoint_check() paths fails after
arch_validate_hwbkpt_settings() was called, then we can not simply restore
bp_addr/bp_type/bp_len and do _perf_event_enable(). We need another
modify_user_hw_breakpoint_check() or validate_hw_breakpoint().

Note that arch_validate_hwbkpt_settings() updates arch_hw_breakpoint according
to bp.attr, the restored bp->attr.bp_addr/bp_typebp_len have no effect if we
call _perf_event_enable() after the failure.

Or I am totally confused?

Oleg.