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[95.90.187.85]) by smtp.gmail.com with ESMTPSA id h30-20020a056402095e00b00412b81dd96esm3666478edz.29.2022.04.03.04.41.50 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sun, 03 Apr 2022 04:41:51 -0700 (PDT) Message-ID: Date: Sun, 3 Apr 2022 13:41:50 +0200 Precedence: bulk X-Mailing-List: linux-staging@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.7.0 Subject: Re: staging: r8188eu: how to handle nested mutex under spinlock Content-Language: en-US To: "Fabio M. De Francesco" Cc: Greg KH , Larry Finger , Phillip Potter , "open list:STAGING SUBSYSTEM" , Linux Kernel Mailing List References: <356c24cf-625b-eea2-2c04-ce132d881cac@gmail.com> <1813843.tdWV9SEqCh@leap> <942bbcb6-725d-9b47-5dfe-f105d30ea6b7@gmail.com> <7365301.EvYhyI6sBW@leap> From: Michael Straube In-Reply-To: <7365301.EvYhyI6sBW@leap> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit 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