Re: [PATCH v2 2/2] staging: r8188eu: Use kzalloc() with GFP_ATOMIC in atomic context

Fabio M. De Francesco
2022-02-17T09:32:23Z

On marted? 15 febbraio 2022 17:10:12 CET Greg Kroah-Hartman wrote:
> On Tue, Feb 08, 2022 at 07:04:26PM +0100, Fabio M. De Francesco wrote:
> > Use the GFP_ATOMIC flag of kzalloc() with two memory allocation in rtw_set_key()
> > because it is not allowed to sleep while it executes in atomic context.
> >
> > With the GFP_ATOMIC type flag, the allocation is high priority and thus it
> > cannot sleep.
> >
> > This issue is detected by Smatch which emits the following warning:
> >
> > "drivers/staging/r8188eu/core/rtw_mlme.c:1603 rtw_set_key() warn: sleeping in atomic context".
> >
> > 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@gmail.com>
> > ---
> > drivers/staging/r8188eu/core/rtw_mlme.c | 4 ++--
> > 1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/staging/r8188eu/core/rtw_mlme.c b/drivers/staging/r8188eu/core/rtw_mlme.c
> > index f5b2df72e0f4..860835e29b79 100644
> > --- a/drivers/staging/r8188eu/core/rtw_mlme.c
> > +++ b/drivers/staging/r8188eu/core/rtw_mlme.c
> > @@ -1600,12 +1600,12 @@ int rtw_set_key(struct adapter *adapter, struct security_priv *psecuritypriv, in
> > struct mlme_priv *pmlmepriv = &adapter->mlmepriv;
> > int res = _SUCCESS;
> >
> > - pcmd = kzalloc(sizeof(*pcmd), GFP_KERNEL);
> > + pcmd = kzalloc(sizeof(*pcmd), GFP_ATOMIC);
> > if (!pcmd) {
> > res = _FAIL; /* try again */
> > goto exit;
> > }
> > - psetkeyparm = kzalloc(sizeof(*psetkeyparm), GFP_KERNEL);
> > + psetkeyparm = kzalloc(sizeof(*psetkeyparm), GFP_ATOMIC);
> > if (!psetkeyparm) {
> > kfree(pcmd);
> > res = _FAIL;
> > --
> > 2.34.1
>
> What code path is calling this in atomic context?
>
> thanks,
>
> greg k-h
>
I blindly trusted Smatch and didn't check properly :(

Now I'm pretty sure that all(?) the code paths that lead to those kzalloc() do
not call rtw_set_key() in atomic context.

The only calls chain that seemed to call rtw_set_key() in atomic context was
rtw_set_key() <- ips_leave() <- _rtw_pwr_wakeup() <- rtw_set_802_11_disassociate()
but Smatch (and I) missed that, immediately before calling ips_leave(), an 'if'
condition makes _rtw_pwr_wakeup() exit and return to rtw_set_802_11_disassociate().

Therefore, please drop this patch.

Thanks,

Fabio M. De Francesco