Re: [PATCH 1/1] driver core: Remove warning on driver unbinding

From: Saravana Kannan <saravanak@google.com>
To: Herve Codina <herve.codina@bootlin.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	"Rafael J. Wysocki" <rafael@kernel.org>,
	linux-kernel@vger.kernel.org,
	Allan Nielsen <allan.nielsen@microchip.com>,
	Horatiu Vultur <horatiu.vultur@microchip.com>,
	Steen Hegelund <steen.hegelund@microchip.com>,
	Thomas Petazzoni <thomas.petazzoni@bootlin.com>,
	stable@vger.kernel.org
Subject: Re: [PATCH 1/1] driver core: Remove warning on driver unbinding
Date: Fri, 10 Nov 2023 17:42:26 -0800	[thread overview]
Message-ID: <CAGETcx-Mp0uKBF_BWFFBUm=eVOp8xhxF3+znFB8vTaFwpJWTnw@mail.gmail.com> (raw)
In-Reply-To: <20231110080241.702999-1-herve.codina@bootlin.com>

On Fri, Nov 10, 2023 at 12:02 AM Herve Codina <herve.codina@bootlin.com> wrote:
>
> During driver unbinding, __device_links_no_driver() can raise the
> following warning:
>    --- 8< ---
>    WARNING: CPU: 0 PID: 166 at drivers/base/core.c:1426 __device_links_no_driver+0xac/0xb4
>    ...
>    Call trace:
>    __device_links_no_driver+0xac/0xb4
>    device_links_driver_cleanup+0xa8/0xf0
>    device_release_driver_internal+0x204/0x240
>    device_release_driver+0x18/0x24
>    bus_remove_device+0xcc/0x10c
>    device_del+0x158/0x414
>    platform_device_del.part.0+0x1c/0x88
>    platform_device_unregister+0x24/0x40
>    of_platform_device_destroy+0xfc/0x10c
>    device_for_each_child_reverse+0x64/0xb4
>    devm_of_platform_populate_release+0x4c/0x84
>    release_nodes+0x5c/0x90
>    devres_release_all+0x8c/0xdc
>    device_unbind_cleanup+0x18/0x68
>    device_release_driver_internal+0x20c/0x240
>    device_links_unbind_consumers+0xe0/0x108
>    device_release_driver_internal+0xf0/0x240
>    driver_detach+0x50/0x9c
>    bus_remove_driver+0x6c/0xbc
>    driver_unregister+0x30/0x60
>    ...
>    --- 8< ---
>
> This warning is raised because, during device removal, we unlink a
> consumer while its supplier links.status is DL_DEV_UNBINDING.
> Even if the link is not a SYNC_STATE_ONLY, the warning should not
> appear in that case.
>
> Filter out this warning in case of the supplier driver is unbinding.
>
> Fixes: 8c3e315d4296 ("driver core: Update device link status correctly for SYNC_STATE_ONLY links")

Wrong Fixes tag. I just added the SYNC_STATE_ONLY exception. The issue
has been there since before.

> Cc: stable@vger.kernel.org
> Signed-off-by: Herve Codina <herve.codina@bootlin.com>
> ---
>  drivers/base/core.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/base/core.c b/drivers/base/core.c
> index 17f2568e0a79..f4b09691998e 100644
> --- a/drivers/base/core.c
> +++ b/drivers/base/core.c
> @@ -1423,7 +1423,8 @@ static void __device_links_no_driver(struct device *dev)
>                 if (link->supplier->links.status == DL_DEV_DRIVER_BOUND) {
>                         WRITE_ONCE(link->status, DL_STATE_AVAILABLE);
>                 } else {
> -                       WARN_ON(!(link->flags & DL_FLAG_SYNC_STATE_ONLY));
> +                       WARN_ON(!(link->flags & DL_FLAG_SYNC_STATE_ONLY) &&
> +                               link->supplier->links.status != DL_DEV_UNBINDING);

Don't delete the warning please. Make it better so it doesn't warn
when it shouldn't.

This combined with the other patches you sent make me think this is
more of an issue in the device removal ordering than an actual issue
with the warning. I'm not fully convinced the warning is incorrect
yet.

-Saravana

>                         WRITE_ONCE(link->status, DL_STATE_DORMANT);
>                 }
>         }
> --
> 2.41.0
>