linux-kernel - Re: [PATCH][RFC] perf/x86: avoid false-positives hard lockup

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Date:   Thu, 10 Oct 2019 11:46:37 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Li RongQing <lirongqing@...du.com>
Cc:     mingo@...hat.com, acme@...nel.org, mark.rutland@....com,
        alexander.shishkin@...ux.intel.com, jolsa@...hat.com,
        namhyung@...nel.org, tglx@...utronix.de, bp@...en8.de,
        hpa@...or.com, x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH][RFC] perf/x86: avoid false-positives hard lockup

On Thu, Oct 10, 2019 at 04:41:38PM +0800, Li RongQing wrote:
> if perf counter is used as nmi watchdog, and twice nmi in soft
> watchdog sample period will trigger hard lockup
> 
> make sure left time is not less than soft watchdog period by
> compared with 3/5 period to skip forward, since soft watchdog
> sample period is 2/5 of watchdog_thresh, nmi watchdog sample
> period, computed by set_sample_period
> 
> Signed-off-by: Li RongQing <lirongqing@...du.com>
> ---
>  arch/x86/events/core.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
> index 7b21455d7504..1f5309456d4c 100644
> --- a/arch/x86/events/core.c
> +++ b/arch/x86/events/core.c
> @@ -1196,7 +1196,11 @@ int x86_perf_event_set_period(struct perf_event *event)
>  	/*
>  	 * If we are way outside a reasonable range then just skip forward:
>  	 */
> +#ifdef CONFIG_HARDLOCKUP_DETECTOR_PERF
> +	if (unlikely(left <= -(period * 3 / 5))) {
> +#else
>  	if (unlikely(left <= -period)) {
> +#endif

NAK. This is 100% the wrong place to do anything like that.