From: Ming Lei Subject: Re: INFO: task hung in blk_queue_enter Date: Sat, 2 Jun 2018 12:54:02 +0800 Message-ID: <20180602045353.GA20257@ming.t460p> References: <6db16aa3a7c56b6dcca2d10b4e100a780c740081.camel@wdc.com> <201805220652.BFH82351.SMQFFOJOtFOVLH@I-love.SAKURA.ne.jp> <201805222020.FEJ82897.OFtJMFHOVLQOSF@I-love.SAKURA.ne.jp> <25708e84-6f35-04c3-a2e4-6854f0ed9e78@I-love.SAKURA.ne.jp> <20180601234946.GA655@ming.t460p> <95c419d8-7f19-f9c0-a53f-3d381fe93176@kernel.dk> <20180602023622.GA2306@ming.t460p> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Tetsuo Handa , Bart.VanAssche@wdc.com, dvyukov@google.com, linux-kernel@vger.kernel.org, linux-block@vger.kernel.org, jthumshirn@suse.de, alan.christopher.jenkins@gmail.com, syzbot+c4f9cebf9d651f6e54de@syzkaller.appspotmail.com, martin.petersen@oracle.com, dan.j.williams@intel.com, hch@lst.de, oleksandr@natalenko.name, martin@lichtvoll.de, hare@suse.com, syzkaller-bugs@googlegroups.com, ross.zwisler@linux.intel.com, keith.busch@intel.com, linux-ext4@vger.kernel.org To: Jens Axboe Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org On Fri, Jun 01, 2018 at 10:31:13PM -0600, Jens Axboe wrote: > On 6/1/18 8:36 PM, Ming Lei wrote: > >> clear the bit when we need to, potentially even adding a debug check to > >> blk_queue_enter_live() that complains if the ref was not already > >> elevated. Though that would be expensive, compared to the percpu inc > >> now. Not saying the bit is necessarily the best way forward, but I do > >> like it a LOT more than adding an argument to generic_make_request. > > > > We may introduce generic_make_request_with_ref() for blk_queue_split(), > > what do you think of the following patch? > > Functionally it'll work as well. If you are fine with this one, I'm glad to prepare for a normal one, so that we can save one precious bio flag, and the total number is just 13. > > > In DM or MD, there is the following use case: > > > > 1) bio comes from fs, then one clone is made from this bio > > > > 2) the cloned bio is submitted via generic_make_request() from > > another context, such as wq. > > > > 3) then the flag of BIO_QUEUE_ENTERED is inherited and causes > > the queue usage counter isn't held. > > We don't copy flags on a clone. Yeah, you are right, seems I ignored that. Thanks, Ming