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Sat, 2 Mar 2019 02:58:00 -0600 Received: from [172.22.217.208] (ileax41-snat.itg.ti.com [10.172.224.153]) by dflp33.itg.ti.com (8.14.3/8.13.8) with ESMTP id x228vtIn009809; Sat, 2 Mar 2019 02:57:56 -0600 Subject: Re: [PATCH v3] cfi: fix deadloop in cfi_cmdset_0002.c do_write_buffer To: Tokunori Ikegami , "'liujian (CE)'" CC: "'Boris Brezillon'" , "'Tokunori Ikegami'" , "bbrezillon@kernel.org" , "ikegami@allied-telesis.co.jp" , "richard@nod.at" , "linux-kernel@vger.kernel.org" , "marek.vasut@gmail.com" , "linux-mtd@lists.infradead.org" , "computersforpeace@gmail.com" , "dwmw2@infradead.org" , "keescook@chromium.org" References: <1551189648-58073-1-git-send-email-liujian56@huawei.com> <016001d4cf71$865e7b60$931b7220$@gmail.com> <4F88C5DDA1E80143B232E89585ACE27D0264F137@DGGEMM528-MBX.china.huawei.com> <20190228164228.734ede80@collabora.com> <005a01d4d03e$39b0e0f0$ad12a2d0$@yahoo.co.jp> <4b3bc01a-3632-5dde-f683-94744ee7179d@ti.com> <000501d4d050$38eca160$aac5e420$@gmail.com> <20190301184317.6bad546f@collabora.com> <001c01d4d057$f68572e0$e39058a0$@yahoo.co.jp> From: Vignesh Raghavendra Message-ID: Date: Sat, 2 Mar 2019 14:27:54 +0530 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.5.1 MIME-Version: 1.0 In-Reply-To: <001c01d4d057$f68572e0$e39058a0$@yahoo.co.jp> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 8bit X-EXCLAIMER-MD-CONFIG: e1e8a2fd-e40a-4ac6-ac9b-f7e9cc9ee180 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 01-Mar-19 11:25 PM, Tokunori Ikegami wrote: >>>> [...] >>>>>>>>> In function do_write_buffer(), in the for loop, there is a >>>>>>>>> case chip_ready() returns 1 while chip_good() returns 0, so >>>>>>>>> it never break the loop. >>>>>>>>> To fix this, chip_good() is enough and it should timeout if >>>>>>>>> it stay bad for a while. >>>>>>>>> >>>>>>>>> Fixes: dfeae1073583("mtd: cfi_cmdset_0002: Change write >>>>>>>>> buffer to check correct value") >>>>>>>>> Signed-off-by: Yi Huaijie >>>>>>>>> Signed-off-by: Liu Jian >>>>>>>>> Reviewed-by: Tokunori Ikegami >>>>>>>>> --- >>>>>>>>> v2->v3: >>>>>>>>> Follow Vignesh's advice: >>>>>>>>> add one more check for check_good() even when time_after() >>>>>>>>> returns >>>>>> true. >>>>>>>>> >>>>>>>>> drivers/mtd/chips/cfi_cmdset_0002.c | 2 +- >>>>>>>>> 1 file changed, 1 insertion(+), 1 deletion(-) >>>>>>>>> >>>>>>>>> diff --git a/drivers/mtd/chips/cfi_cmdset_0002.c >>>>>>>>> b/drivers/mtd/chips/cfi_cmdset_0002.c >>>>>>>>> index 72428b6..3da2376 100644 >>>>>>>>> --- a/drivers/mtd/chips/cfi_cmdset_0002.c >>>>>>>>> +++ b/drivers/mtd/chips/cfi_cmdset_0002.c >>>>>>>>> @@ -1876,7 +1876,7 @@ static int __xipram >>>>>>>>> do_write_buffer(struct map_info *map, struct flchip *chip, >>>>>>>>> continue; >>>>>>>>> } >>>>>>>>> >>>>>>>>> - if (time_after(jiffies, timeo) >>>>>>>>> && !chip_ready(map, adr)) >>>>>>>>> + if (time_after(jiffies, timeo) >>>>>>>>> && !chip_good(map, adr, datum)) >>>>>>>> >>>>>>>> Just another idea to understand easily. >>>>>>>> >>>>>>>> unsigned long now = jiffies; >>>>>>>> >>>>>>>> if (chip_good(map, adr, datum)) { >>>>>>>> xip_enable(map, chip, adr); >>>>>>>> goto op_done; >>>>>>>> } >>>>>>>> >>>>>>>> if (time_after(now, timeo) { >>>>>>>> break; >>>>>>>> } >>>>>>>> >>>>>>> >>>>>>> Thank you~. It is more easier to understand！ >>>>>>> If there are no other comments, I will send new patch again ): >>>>>> >>>>>> Except this version no longer does what Vignesh suggested. See >>>>>> how you no longer test if chip_good() is true if time_after() >>>>>> returns true. So, imagine the thread entering this function is >>>>>> preempted just after the first chip_good() test, and resumed a >>>>>> few ms later. time_after() will return true, but chip_good() >>>>>> might also return true, and you ignore it. >>>>> >>>>> I think that the following 3 versions will be worked for >>>>> time_after() >>>> as a same result and follow the Vignesh-san suggestion. >>>>> >>>> >>>> As Boris explained above version 3 does not really follow my >>>> suggestion... Please see below >>>> >>>>> 1. Original Vignesh-san suggestion >>>>> >>>>> if (chip_good(map, adr, datum)) { >>>>> xip_enable(map, chip, adr); >>>>> goto op_done; >>>>> } >>>>> >>>>> if (time_after(jiffies, timeo)) { >>>>> /* Test chip_good() if TRUE incorrectly again so >>>>> write >>>> failure by time_after() can be avoided. */ >>>>> if (chip_good(map, adr, datum)) { >>>>> xip_enable(map, chip, adr); >>>>> goto op_done; >>>>> } >>>>> break; >>>>> } >>>>> >>>> >>>> >>>> Right, here we check chip_good() once _even when time_after() is >>>> true_ to avoid _spurious_ timeout >>>> >>>>> 2. Liujian-san v3 patch >>>>> >>>>> /* Test chip_good() if FALSE correctly so write failure >>>>> by >>>> time_after() can be avoided. */ >>>>> if (time_after(jiffies, timeo) && !chip_good(map, adr)) >>>>> break; >>>>> >>>>> if (chip_good(map, adr, datum)) { >>>>> xip_enable(map, chip, adr); >>>>> goto op_done; >>>>> } >>>>> >>>> >>>> This is a better version of 1 >>>> >>>>> 3. My idea >>>>> >>>>> /* Save current jiffies value before chip_good() to avoid >>>>> write >>>> failure by time_after() without testing chip_good() again. */ >>>>> unsigned long now = jiffies; >>>>> >>>>> if (chip_good(map, adr, datum)) { >>>>> xip_enable(map, chip, adr); >>>>> goto op_done; >>>>> } >>>>> >>>> >>>> What if thread gets pre-empted at this point and is re-scheduled >>>> exactly after timeo jiffies have elapsed? Below check would be true >>>> and exit loop >>> >>> I think that the jiffies value now is save before chip_good() so >>> below check would be false and not exit loop. >> Ok, I get it now. >> True, I overlooked that part, and so Vignesh did. This proves one >> thing: code is not easier to follow with your version. IMO, if we want >> to make things clear, we should add a comment to Liujian's explaining >> why the extra test after time_after(jiffies, timeo) is needed. > > I see so I am okay with the change of Liujian-san v3 patch. > Also agree with the comment to be added. > Right, I like the current patch from Liujian, because its more consistent with the existing code in this file. Liujian, Could you re-post with a comment added as suggested above? Regards Vignesh