linux-kernel - Re: [PATCH V9] devcoredump: add context check in dev

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Date:   Mon, 26 Sep 2022 08:44:28 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     duoming@....edu.cn
Cc:     johannes@...solutions.net, linux-kernel@...r.kernel.org,
        rafael@...nel.org
Subject: Re: [PATCH V9] devcoredump: add context check in dev_coredumpm

On Mon, Sep 26, 2022 at 02:38:28PM +0800, duoming@....edu.cn wrote:
> Hello,
> 
> On Mon, 26 Sep 2022 08:27:58 +0200 Greg KH wrote:
> 
> > On Mon, Sep 26, 2022 at 02:16:09PM +0800, Duoming Zhou wrote:
> > > The dev_coredumpm(), dev_coredumpv() and dev_coredumpsg() 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 adds context check in dev_coredumpm() in order to show
> > > dev_coredumpm() and its callers could not be used in atomic context.
> > > 
> > > What's more, this change can allow the api to evolve and will not
> > > influence the users that call this api.
> > > 
> > > Fixes: 833c95456a70 ("device coredump: add new device coredump class")
> > > Signed-off-by: Duoming Zhou <duoming@....edu.cn>
> > > ---
> > > Changes in v9:
> > >   - Add context check in dev_coredumpm().
> > > 
> > >  drivers/base/devcoredump.c | 3 +++
> > >  1 file changed, 3 insertions(+)
> > > 
> > > diff --git a/drivers/base/devcoredump.c b/drivers/base/devcoredump.c
> > > index f4d794d6bb8..806ee872f5f 100644
> > > --- a/drivers/base/devcoredump.c
> > > +++ b/drivers/base/devcoredump.c
> > > @@ -255,6 +255,9 @@ void dev_coredumpm(struct device *dev, struct module *owner,
> > >  	struct devcd_entry *devcd;
> > >  	struct device *existing;
> > >  
> > > +	if (!gfpflags_normal_context(gfp))
> > > +		goto free;
> > 
> > Wait, this just broke things for no good reason if a caller happened to
> > have set a GFP flag that we do not like at the moment.
> > 
> > What code now does not work that previously did work with this change?
> 
> I found that all users in the kernel call the dev_coredumpv(), dev_coredumpm() and
> dev_coredumpsg() with "GFP_KERNEL". So this change will not influence the existing users.

Great, so there is no need for this, and it does not "fix" any commit.

confused,

greg k-h