netdev - Re: [PATCH v7 1/2] devcoredump: remove the useless gfp_t parameter in dev_coredumpv and dev

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Date:   Wed, 17 Aug 2022 14:43:29 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Duoming Zhou <duoming@....edu.cn>
Cc:     linux-kernel@...r.kernel.org, linux-wireless@...r.kernel.org,
        briannorris@...omium.org, amitkarwar@...il.com,
        ganapathi017@...il.com, sharvari.harisangam@....com,
        huxinming820@...il.com, kvalo@...nel.org, davem@...emloft.net,
        edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com,
        netdev@...r.kernel.org, johannes@...solutions.net,
        rafael@...nel.org
Subject: Re: [PATCH v7 1/2] devcoredump: remove the useless gfp_t parameter
 in dev_coredumpv and dev_coredumpm

On Wed, Aug 17, 2022 at 08:39:12PM +0800, Duoming Zhou wrote:
> The dev_coredumpv() and dev_coredumpm() could not be used in atomic
> context, because they call kvasprintf_const() and kstrdup() with
> GFP_KERNEL parameter. The process is shown below:
> 
> dev_coredumpv(.., gfp_t gfp)
>   dev_coredumpm(.., gfp_t gfp)
>     dev_set_name
>       kobject_set_name_vargs
>         kvasprintf_const(GFP_KERNEL, ...); //may sleep
>           kstrdup(s, GFP_KERNEL); //may sleep
> 
> This patch removes gfp_t parameter of dev_coredumpv() and dev_coredumpm()
> and changes the gfp_t parameter of kzalloc() in dev_coredumpm() to
> GFP_KERNEL in order to show they could not be used in atomic context.
> 
> Fixes: 833c95456a70 ("device coredump: add new device coredump class")
> Reviewed-by: Brian Norris <briannorris@...omium.org>
> Reviewed-by: Johannes Berg <johannes@...solutions.net>
> Signed-off-by: Duoming Zhou <duoming@....edu.cn>
> ---
> Changes in v7:
>   - Remove gfp_t flag in amdgpu device.

Again, this creates a "flag day" where we have to be sure we hit all
users of this api at the exact same time.  This will prevent any new
driver that comes into a maintainer tree during the next 3 months from
ever being able to use this api without cauing build breakages in the
linux-next tree.

Please evolve this api to work properly for everyone at the same time,
like was previously asked for so that we can take this change.  It will
take 2 releases, but that's fine.

thanks,

greg k-h