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SubjectRe: [PATCH V9] devcoredump: add context check in dev_coredumpm
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@zju.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.

Best regards,
Duoming Zhou
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