linux-kernel - Re: [PATCH v3] mwifiex: fix sleep in atomic context bugs caused by dev

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Message-ID: <6d8c70c0.2b1f1.180eff156be.Coremail.duoming@zju.edu.cn>
Date:   Mon, 23 May 2022 16:03:32 +0800 (GMT+08:00)
From:   duoming@....edu.cn
To:     linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] mwifiex: fix sleep in atomic context bugs caused by
 dev_coredumpv

Hello,

On Mon, 23 May 2022 08:31:46 +0200 Greg KH wrote:

> > There are sleep in atomic context bugs when uploading device dump
> > data in mwifiex. The root cause is that dev_coredumpv could not
> > be used in atomic contexts, because it calls dev_set_name which
> > include operations that may sleep. The call tree shows execution
> > paths that could lead to bugs:
> > 
> >    (Interrupt context)
> > fw_dump_timer_fn
> >   mwifiex_upload_device_dump
> >     dev_coredumpv(..., GFP_KERNEL)
> >       dev_coredumpm()
> >         kzalloc(sizeof(*devcd), gfp); //may sleep
> >         dev_set_name
> >           kobject_set_name_vargs
> >             kvasprintf_const(GFP_KERNEL, ...); //may sleep
> >             kstrdup(s, GFP_KERNEL); //may sleep
> > 
> > In order to let dev_coredumpv support atomic contexts, this patch
> > changes the gfp_t parameter of kvasprintf_const and kstrdup in
> > kobject_set_name_vargs from GFP_KERNEL to GFP_ATOMIC. What's more,
> > In order to mitigate bug, this patch changes the gfp_t parameter
> > of dev_coredumpv from GFP_KERNEL to GFP_ATOMIC.
> > 
> > Fixes: 57670ee882d4 ("mwifiex: device dump support via devcoredump framework")
> > Signed-off-by: Duoming Zhou <duoming@....edu.cn>
> > ---
> > Changes in v3:
> >   - Let dev_coredumpv support atomic contexts.
> > 
> >  drivers/net/wireless/marvell/mwifiex/main.c | 2 +-
> >  lib/kobject.c                               | 4 ++--
> >  2 files changed, 3 insertions(+), 3 deletions(-)
> > 
> > diff --git a/drivers/net/wireless/marvell/mwifiex/main.c b/drivers/net/wireless/marvell/mwifiex/main.c
> > index ace7371c477..258906920a2 100644
> > --- a/drivers/net/wireless/marvell/mwifiex/main.c
> > +++ b/drivers/net/wireless/marvell/mwifiex/main.c
> > @@ -1116,7 +1116,7 @@ void mwifiex_upload_device_dump(struct mwifiex_adapter *adapter)
> >  	mwifiex_dbg(adapter, MSG,
> >  		    "== mwifiex dump information to /sys/class/devcoredump start\n");
> >  	dev_coredumpv(adapter->dev, adapter->devdump_data, adapter->devdump_len,
> > -		      GFP_KERNEL);
> > +		      GFP_ATOMIC);
> >  	mwifiex_dbg(adapter, MSG,
> >  		    "== mwifiex dump information to /sys/class/devcoredump end\n");
> >  
> > diff --git a/lib/kobject.c b/lib/kobject.c
> > index 5f0e71ab292..7672c54944c 100644
> > --- a/lib/kobject.c
> > +++ b/lib/kobject.c
> > @@ -254,7 +254,7 @@ int kobject_set_name_vargs(struct kobject *kobj, const char *fmt,
> >  	if (kobj->name && !fmt)
> >  		return 0;
> >  
> > -	s = kvasprintf_const(GFP_KERNEL, fmt, vargs);
> > +	s = kvasprintf_const(GFP_ATOMIC, fmt, vargs);
> >  	if (!s)
> >  		return -ENOMEM;
> >  
> > @@ -267,7 +267,7 @@ int kobject_set_name_vargs(struct kobject *kobj, const char *fmt,
> >  	if (strchr(s, '/')) {
> >  		char *t;
> >  
> > -		t = kstrdup(s, GFP_KERNEL);
> > +		t = kstrdup(s, GFP_ATOMIC);
> >  		kfree_const(s);
> >  		if (!t)
> >  			return -ENOMEM;
> 
> Please no, you are hurting the whole kernel because of one odd user.
> Please do not make these calls under atomic context.

Thanks for your time and suggestions. I will remove the gfp_t parameter of dev_coredumpv
in order to show it could not be used in atomic context.

Best Regards,
Duoming Zhou