linux-kernel - Re: [PATCH v3 6/8] remoteproc: Introduce "panic" callback in ops

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Message-ID: <158164806895.184098.244699295706516537@swboyd.mtv.corp.google.com>
Date:   Thu, 13 Feb 2020 18:41:08 -0800
From:   Stephen Boyd <swboyd@...omium.org>
To:     Bjorn Andersson <bjorn.andersson@...aro.org>,
        Ohad Ben-Cohen <ohad@...ery.com>
Cc:     Andy Gross <agross@...nel.org>, Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        linux-arm-msm@...r.kernel.org, linux-remoteproc@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        Sibi Sankar <sibis@...eaurora.org>,
        Rishabh Bhatnagar <rishabhb@...eaurora.org>
Subject: Re: [PATCH v3 6/8] remoteproc: Introduce "panic" callback in ops

Quoting Bjorn Andersson (2020-02-10 16:50:57)
> diff --git a/drivers/remoteproc/remoteproc_core.c b/drivers/remoteproc/remoteproc_core.c
> index 097f33e4f1f3..8b6932027d36 100644
> --- a/drivers/remoteproc/remoteproc_core.c
> +++ b/drivers/remoteproc/remoteproc_core.c
> @@ -2216,10 +2218,53 @@ void rproc_report_crash(struct rproc *rproc, enum rproc_crash_type type)
>  }
>  EXPORT_SYMBOL(rproc_report_crash);
>  
> +static int rproc_panic_handler(struct notifier_block *nb, unsigned long event,
> +                              void *ptr)
> +{
> +       unsigned int longest = 0;
> +       struct rproc *rproc;
> +       unsigned int d;
> +       int locked;
> +
> +       locked = mutex_trylock(&rproc_list_mutex);
> +       if (!locked) {
> +               pr_err("Failed to acquire rproc list lock, won't call panic functions\n");
> +               return NOTIFY_DONE;
> +       }
> +
> +       list_for_each_entry(rproc, &rproc_list, node) {
> +               if (!rproc->ops->panic || rproc->state != RPROC_RUNNING)
> +                       continue;
> +
> +               d = rproc->ops->panic(rproc);
> +               if (d > longest)
> +                       longest = d;

Could be

	d = max(longest, d);

> +       }
> +
> +       mutex_unlock(&rproc_list_mutex);
> +
> +       /* Delay panic for the longest requested duration */
> +       mdelay(longest);

Is this to flush caches? Maybe indicate that in the comment.

> +
> +       return NOTIFY_DONE;
> +}
> +
> +static void __init rproc_init_panic(void)
> +{
> +       rproc_panic_nb.notifier_call = rproc_panic_handler;
> +       atomic_notifier_chain_register(&panic_notifier_list, &rproc_panic_nb);

This is an atomic notifier, but the notifier function takes a mutex,
which sleeps. It should use spinlocks, and never sleep, given that panic
can be called from anywhere.

> +}
> +
> diff --git a/include/linux/remoteproc.h b/include/linux/remoteproc.h
> index 16ad66683ad0..14f05f26cbcd 100644
> --- a/include/linux/remoteproc.h
> +++ b/include/linux/remoteproc.h
> @@ -369,6 +369,8 @@ enum rsc_handling_status {
>   *                     expects to find it
>   * @sanity_check:      sanity check the fw image
>   * @get_boot_addr:     get boot address to entry point specified in firmware
> + * @panic:     optional callback to react to system panic, core will delay
> + *             panic at least the returned number of milliseconds
>   */
>  struct rproc_ops {
>         int (*start)(struct rproc *rproc);
> @@ -383,6 +385,7 @@ struct rproc_ops {
>         int (*load)(struct rproc *rproc, const struct firmware *fw);
>         int (*sanity_check)(struct rproc *rproc, const struct firmware *fw);
>         u32 (*get_boot_addr)(struct rproc *rproc, const struct firmware *fw);
> +       unsigned int (*panic)(struct rproc *rproc);

Maybe should be unsigned long to match other "timeouts" in the kernel.