Messages in this thread |  | | Date | Sun, 3 Apr 2022 13:41:50 +0200 | Subject | Re: staging: r8188eu: how to handle nested mutex under spinlock | From | Michael Straube <> |
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On 4/3/22 13:17, Fabio M. De Francesco wrote: > On domenica 3 aprile 2022 13:08:35 CEST Michael Straube wrote: >> On 4/3/22 12:49, Fabio M. De Francesco wrote: >>> On domenica 3 aprile 2022 12:43:04 CEST Fabio M. De Francesco wrote: >>>> On sabato 2 aprile 2022 22:47:27 CEST Michael Straube wrote: >>>>> Hi all, >>>>> >>>>> smatch reported a sleeping in atomic context. >>>>> >>>>> rtw_set_802_11_disassociate() <- disables preempt >>>>> -> _rtw_pwr_wakeup() >>>>> -> ips_leave() >>>>> >>>>> rtw_set_802_11_disassociate() takes a spinlock and ips_leave() uses a >>>>> mutex. >>>>> >>>>> I'm fairly new to the locking stuff, but as far as I know this is not a >>>>> false positive since mutex can sleep, but that's not allowed under a >>>>> spinlock. >>>>> >>>>> What is the best way to handle this? >>>>> I'm not sure if converting the mutex to a spinlock (including all the >>>>> other places where the mutex is used) is the right thing to do? >>>>> >>>>> thanks, >>>>> Michael >>>>> >>>> Hi Michael, >>>> >>>> No, this is a false positive: ips_leave is never called under spinlocks. >>>> Some time ago I blindly trusted Smatch and submitted a patch for what you >>>> are reporting just now again. Soon after submission I realized it and >>>> then I had to ask Greg to discard my patch. >>>> >>>> Please read the related thread: >>>> >>>> [PATCH] staging: r8188eu: Use kzalloc() with GFP_ATOMIC in atomic context >>>> https://lore.kernel.org/lkml/20220206225943.7848-1-fmdefrancesco@gmail.com/ >>>> >>>> Thanks, >>>> >>>> Fabio >>> >>> I'm sorry, the correct link is the following: >>> [PATCH v2 2/2] staging: r8188eu: Use kzalloc() with GFP_ATOMIC in atomic context >>> https://lore.kernel.org/lkml/20220208180426.27455-3-fmdefrancesco@gmail.com/ >>> >>> Fabio >>> >> >> Hi Fabio, >> >> Ah I see now, thanks. Well, I think the code is not very clear and easy >> to follow here. Perhaps we should refactor this area someday to avoid >> future confusions. >> >> regards, >> Michael >> > Soon after I sent the email above, I read yours anew. The issue I were trying > to address were different than what you noticed today. I didn't even see that > we were in nested mutexes under spinlocks and bottom halves disabled. I just > saw those kmalloc() with GFP_KERNEL. > > You are noticing something one layer up. And you are right, this is a real > issue. Larry's suggestion is the only correct one for fixing this. > > I've analyzed and reviewed some code in the tty layer that implements the > same solution that Larry is talking about. Let me find the link and I'll > soon send it to you, so that you might be inspired from that implementation. > > Sorry for the confusion. > > Thanks, > > Fabio > > >
Hi Fabio,
wait..
rtw_set_802_11_disassociate() calls rtw_pwr_wakeup() only if check_fwstate(pmlmepriv, _FW_LINKED) is true.
if (check_fwstate(pmlmepriv, _FW_LINKED)) { rtw_disassoc_cmd(padapter, 0, true); rtw_indicate_disconnect(padapter); rtw_free_assoc_resources(padapter, 1); rtw_pwr_wakeup(padapter); }
in rtw_pwr_wakeup() there is the same check and if it is true the function returns before calling ips_leave().
if (check_fwstate(pmlmepriv, _FW_LINKED)) { ret = _SUCCESS; goto exit; } if (rf_off == pwrpriv->rf_pwrstate) { if (_FAIL == ips_leave(padapter)) { ret = _FAIL; goto exit; } }
So ips_leave() is not called in atomic context in this case and smatch reports indeed a false positive, or am I wrong?
I have not checked the other calls to rtw_pwr_wakeup().
regards, Michael
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