From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Subject: Re: [PATCH v2] blktrace: Fix potentail deadlock between delete & sysfs ops To: Steven Rostedt Cc: Jens Axboe , Jeff Layton , "J. Bruce Fields" , Ingo Molnar , linux-kernel@vger.kernel.org, linux-block@vger.kernel.org, linux-fsdevel@vger.kernel.org References: <1502916040-18067-1-git-send-email-longman@redhat.com> <20170817093444.3276f7ab@gandalf.local.home> <20170817171007.1ab33b8f@gandalf.local.home> <6bb40f9f-7f55-28b4-812b-a80f05bec6ea@redhat.com> <20170817181320.60b02500@gandalf.local.home> <20170817181818.4ef4acf3@gandalf.local.home> <20170817192343.503fac3d@gandalf.local.home> From: Waiman Long Message-ID: <7073443d-1bf7-c087-6065-1bf73adb97a1@redhat.com> Date: Fri, 18 Aug 2017 09:42:25 -0400 MIME-Version: 1.0 In-Reply-To: <20170817192343.503fac3d@gandalf.local.home> Content-Type: multipart/mixed; boundary="------------067D991C8497D2EEDB39A92D" Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org List-ID: This is a multi-part message in MIME format. --------------067D991C8497D2EEDB39A92D Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit On 08/17/2017 07:23 PM, Steven Rostedt wrote: > On Thu, 17 Aug 2017 18:18:18 -0400 > Steven Rostedt wrote: > >> On Thu, 17 Aug 2017 18:13:20 -0400 >> Steven Rostedt wrote: >> >>> On Thu, 17 Aug 2017 17:27:22 -0400 >>> Waiman Long wrote: >>> >>> >>>> It is actually what the patch is trying to do by checking for the >>>> deletion flag in the mutex_trylock loop. Please note that mutex does not >>>> guarantee FIFO ordering of lock acquisition. As a result, cpu1 may call >>>> mutex_lock() and wait for it while cpu2 can set the deletion flag later >>>> and get the mutex first before cpu1. So checking for the deletion flag >>>> before taking the mutex isn't enough. >>> Yeah, I figured that out already (crossed emails). BTW, how did you >>> trigger this warning. I'm playing around with adding loop devices, >>> volume groups, and logical volumes, and reading the trace files >>> created in the sysfs directory, then removing those items, but it's >>> not triggering the "delete" path. What operation deletes the partition? >> I'm guessing that deleting an actual partition may work (unfortunately, >> my test box has no partition to delete ;-) I'll find another box to >> test on. >> > OK, deleting a partition doesn't trigger the lockdep splat. But I also > added a printk in the BLKPG_DEL_PARTITION case switch, which also > doesn't print. What command do I need to do to trigger that path? > > Thanks, > > -- Steve Attached is a reproducer that was used to trigger the warning. Some tuning may be needed depend on the actual configuration of the test machine. Cheers, Longman --------------067D991C8497D2EEDB39A92D Content-Type: application/x-shellscript; name="run_test.sh" Content-Transfer-Encoding: base64 Content-Disposition: attachment; filename="run_test.sh" IyEvYmluL2Jhc2gKCnRydW5jYXRlIC1zIDFHIHRlc3RmaWxlCnBhcnRlZCAtcyAtLSB0ZXN0 ZmlsZSBta2xhYmVsIGdwdCBta3BhcnQgcHJpbWFyeSAyMDQ4cyAxMDAlCmxvb3BfZGV2aWNl PWBsb3NldHVwIC0tc2hvdyAtZlAgdGVzdGZpbGVgCnBhcnR4IC1kICRsb29wX2RldmljZQpj YXQgL3N5cy9ibG9jay9kbS0yL3RyYWNlL2FjdF9tYXNrIAoK --------------067D991C8497D2EEDB39A92D--