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 22:05:37 +0800 (GMT+08:00)
From:   duoming@....edu.cn
To:     "Greg KH" <gregkh@...uxfoundation.org>
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

Hello,

On Wed, 17 Aug 2022 14:43:29 +0200 Greg KH wrote:

> 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.

Thank you for your reply, I will evolve this api to work properly for everyone.
If there are not any new drivers that use this api during the next 3 months, 
I will send this patch again. Otherwise, I will wait until there are not new
users anymore.

Best regards,
Duoming Zhou