linux-kernel - Re: [PATCH] staging: r8188eu: Use kzalloc() with GFP

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Message-ID: <2743885.88bMQJbFj6@leap>
Date:   Tue, 08 Feb 2022 11:22:40 +0100
From:   "Fabio M. De Francesco" <fmdefrancesco@...il.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Larry Finger <Larry.Finger@...inger.net>,
        Phillip Potter <phil@...lpotter.co.uk>,
        linux-staging@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] staging: r8188eu: Use kzalloc() with GFP_ATOMIC in atomic context

On marted? 8 febbraio 2022 10:33:04 CET Greg Kroah-Hartman wrote:
> On Sun, Feb 06, 2022 at 11:59:43PM +0100, Fabio M. De Francesco wrote:
> > Use the GFP_ATOMIC flag of kzalloc() with two memory allocation in
> > rtw_set_key(). This function is called while holding spinlocks and with
> > disabled bottom halves, therefore it is not allowed to sleep. With the
> > GFP_ATOMIC type flag, the allocation is high priority and cannot sleep.
> > 
> > This issue is detected by Smatch which emits the following warning:
> > drivers/staging/r8188eu/core/rtw_pwrctrl.c:79 ips_leave() warn: sleeping in atomic context
> > drivers/staging/r8188eu/core/rtw_pwrctrl.c:81 ips_leave() warn: sleeping in atomic context
> > 
> > The calls chain (in reverse order) is the following:
> > 
> > rtw_set_key()
> > -> ips_leave()
> > -> -> rtw_pwr_wakeup()
> > -> -> -> rtw_set_802_11_disassociate()
> > 
> > The disable of bottom halves and the acquisition of a spinlock is in
> > rtw_set_802_11_disassociate().
> > 
> > After the changes, the post-commit hook output the following messages:
> > 
> > CHECK: Prefer kzalloc(sizeof(*pcmd)...) over kzalloc(sizeof(struct cmd_obj)...)
> > +       pcmd = kzalloc(sizeof(struct cmd_obj), GFP_ATOMIC);
> > 
> > CHECK: Prefer kzalloc(sizeof(*psetkeyparm)...) over kzalloc(sizeof(struct setkey_parm)...)
> > +       psetkeyparm = kzalloc(sizeof(struct setkey_parm), GFP_ATOMIC).
> > 
> > According to the above "CHECK[S]", use the preferred style in the first
> > kzalloc().
> > 
> > Fixes: 79f712ea994d ("staging: r8188eu: Remove wrappers for kalloc() and kzalloc()")
> > Fixes: 15865124feed ("staging: r8188eu: introduce new core dir for RTL8188eu driver")
> > Signed-off-by: Fabio M. De Francesco <fmdefrancesco@...il.com>
> > ---
> >  drivers/staging/r8188eu/core/rtw_mlme.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > [...]
> 
> You are making two different changes here.  Please do the first patch to
> change the sizeof() change to fix up checkpatch, and then the second one
> for the GFP_ATOMIC change so that if there is a problem with either of
> them we can only revert the offending change.
>
OK, thanks for your reply. I'm about to split this patch in two steps as 
you require.

In the while I've noticed that, after git-reset HARD^, Smatch now points directly 
to the kzalloc() calls and emits a different output:

"drivers/staging/r8188eu/core/rtw_mlme.c:1603 rtw_set_key() warn: sleeping in 
atomic context
  CHECK   drivers/staging/r8188eu/core/rtw_mlme_ext.c".

So now it complains specifically about the first of the two kzalloc[s]() in 
rtw_set_key(). Before sending v2, I'd like to check why when I made v1 it pointed 
to the lines that call rtw_set_key(). You'll see that change in the commit message
of v2.

Thanks,

Fabio
>
> thanks,
> 
> greg k-h
> 
>