linux-kernel - Re: [PATCH v1 1/3] driver core: Don't do deferred probe in parallel with kernel

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Date:   Tue, 7 Jul 2020 17:59:08 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Saravana Kannan <saravanak@...gle.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        "Cc: Android Kernel" <kernel-team@...roid.com>
Subject: Re: [PATCH v1 1/3] driver core: Don't do deferred probe in parallel
 with kernel_init thread

On Wed, Jul 1, 2020 at 9:43 PM Saravana Kannan <saravanak@...gle.com> wrote:
>
> The current deferred probe implementation can mess up suspend/resume
> ordering if deferred probe thread is kicked off in parallel with the
> main initcall thread (kernel_init thread) [1].
>
> For example:
>
> Say device-B is a consumer of device-A.
>
> Initcall thread                                 Deferred probe thread
> ===============                                 =====================
> 1. device-A is added.
> 2. device-B is added.
> 3. dpm_list is now [device-A, device-B].
> 4. driver-A defers probe of device-A.
>                                                 5. device-A is moved to
>                                                    end of dpm_list
>                                                 6. dpm_list is now
>                                                    [device-B, device-A]
> 7. driver-B is registereed and probes device-B.
> 8. dpm_list stays as [device-B, device-A].
>
> The reverse order of dpm_list is used for suspend. So in this case
> device-A would incorrectly get suspended before device-B.
>
> Commit 716a7a259690 ("driver core: fw_devlink: Add support for batching
> fwnode parsing") kicked off the deferred probe thread early during boot
> to run in parallel with the initcall thread and caused suspend/resume
> regressions.  This patch removes the parallel run of the deferred probe
> thread to avoid the suspend/resume regressions.
>
> [1] - https://lore.kernel.org/lkml/CAGETcx8W96KAw-d_siTX4qHB_-7ddk0miYRDQeHE6E0_8qx-6Q@mail.gmail.com/
>
> Fixes: 716a7a259690 ("driver core: fw_devlink: Add support for batching fwnode parsing")
> Signed-off-by: Saravana Kannan <saravanak@...gle.com>
> ---
>  drivers/base/base.h | 1 -
>  drivers/base/core.c | 1 -
>  drivers/base/dd.c   | 5 -----
>  3 files changed, 7 deletions(-)
>
> diff --git a/drivers/base/base.h b/drivers/base/base.h
> index 95c22c0f9036..40fb069a8a7e 100644
> --- a/drivers/base/base.h
> +++ b/drivers/base/base.h
> @@ -153,7 +153,6 @@ extern char *make_class_name(const char *name, struct kobject *kobj);
>  extern int devres_release_all(struct device *dev);
>  extern void device_block_probing(void);
>  extern void device_unblock_probing(void);
> -extern void driver_deferred_probe_force_trigger(void);
>
>  /* /sys/devices directory */
>  extern struct kset *devices_kset;
> diff --git a/drivers/base/core.c b/drivers/base/core.c
> index 67d39a90b45c..35cc9896eb9e 100644
> --- a/drivers/base/core.c
> +++ b/drivers/base/core.c
> @@ -1323,7 +1323,6 @@ void fw_devlink_resume(void)
>                 goto out;
>
>         device_link_add_missing_supplier_links();
> -       driver_deferred_probe_force_trigger();

So it looks like this was not needed after all.

What was the role of it then?

>  out:
>         mutex_unlock(&defer_fw_devlink_lock);
>  }
> diff --git a/drivers/base/dd.c b/drivers/base/dd.c
> index 9a1d940342ac..48ca81cb8ebc 100644
> --- a/drivers/base/dd.c
> +++ b/drivers/base/dd.c
> @@ -164,11 +164,6 @@ static void driver_deferred_probe_trigger(void)
>         if (!driver_deferred_probe_enable)
>                 return;
>
> -       driver_deferred_probe_force_trigger();
> -}
> -
> -void driver_deferred_probe_force_trigger(void)
> -{
>         /*
>          * A successful probe means that all the devices in the pending list
>          * should be triggered to be reprobed.  Move all the deferred devices
> --
> 2.27.0.212.ge8ba1cc988-goog
>