From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mike Snitzer Subject: Re: [PATCH 8/9] dm: Fix two race conditions related to stopping and starting queues Date: Thu, 1 Sep 2016 15:05:05 -0400 Message-ID: <20160901190505.GA12106@redhat.com> References: <18db2396-cd4f-1d52-1ffa-21b9b512eaf4@sandisk.com> <82ff8574-8b73-8ba3-9098-741060f38fca@sandisk.com> <20160901031355.GB4741@redhat.com> <20160901150503.GA11074@redhat.com> <20160901155051.GA11353@redhat.com> <20160901161253.GA11410@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: dm-devel-bounces@redhat.com Errors-To: dm-devel-bounces@redhat.com To: Bart Van Assche Cc: "axboe@kernel.dk" , device-mapper development , "hch@lst.de" List-Id: dm-devel.ids On Thu, Sep 01 2016 at 1:59pm -0400, Bart Van Assche wrote: > On 09/01/2016 09:12 AM, Mike Snitzer wrote: > >On Thu, Sep 01 2016 at 11:50am -0400, > >Mike Snitzer wrote: > > > >>On Thu, Sep 01 2016 at 11:31am -0400, > >>Bart Van Assche wrote: > >> > >>>On 09/01/2016 08:05 AM, Mike Snitzer wrote: > >>>>I've staged most of your changes (with slight tweaks), see: > >>>>https://git.kernel.org/cgit/linux/kernel/git/device-mapper/linux-dm.git/log/?h=dm-4.9 > >>>> > >>>>Only remaining issue is the queue dying race(s) in dm-multipath. > >>> > >>>Thanks Mike! Two minor comments though: > >>>* In dm_start_queue(), I think that the queue_flag_clear_unlocked() > >>> call should be converted into queue_flag_clear() and that it should > >>> be protected by the block layer queue lock. Every call of > >>> queue_flag_clear_unlocked() after block device initialization has > >>> finished is wrong if blk_cleanup_queue() can be called concurrently. > >> > >>OK, I'll have a look. > > > >Please see/test the dm-4.8 and dm-4.9 branches (dm-4.9 being rebased > >ontop of dm-4.8): > >https://git.kernel.org/cgit/linux/kernel/git/device-mapper/linux-dm.git/log/?h=dm-4.8 > >https://git.kernel.org/cgit/linux/kernel/git/device-mapper/linux-dm.git/log/?h=dm-4.9 > > Hello Mike, > > The result of my tests of the dm-4.9 branch is as follows: > * With patch "dm mpath: check if path's request_queue is dying in > activate_path()" I still see every now and then that CPU usage of > one of the kworker threads jumps to 100%. So you're saying that the dying queue check is still needed in the path selector? Would be useful to know why the 100% is occuring. Can you get a stack trace during this time? > * A "if (!blk_queue_stopped(q))" test needs to be added in > dm_stop_queue() to avoid the following hang (that test was present > in my version of the patch that adds the > blk_mq_{freeze,unfreeze}_queue() calls): > > sysrq: SysRq : Show Blocked State > task PC stack pid father > multipathd D ffff8803c8d37b80 0 3242 1 0x00000000 > Call Trace: > [] schedule+0x37/0x90 > [] blk_mq_freeze_queue_wait+0x51/0xb0 > [] blk_mq_freeze_queue+0x15/0x20 > [] dm_stop_queue+0x62/0xc0 [dm_mod] > [] dm_swap_table+0x2fb/0x370 [dm_mod] > [] dev_suspend+0x95/0x220 [dm_mod] > [] ctl_ioctl+0x1fc/0x550 [dm_mod] > [] dm_ctl_ioctl+0xe/0x20 [dm_mod] > [] do_vfs_ioctl+0x8f/0x690 > [] SyS_ioctl+0x3c/0x70 > [] entry_SYSCALL_64_fastpath+0x18/0xa8 OK, I've adjusted accordingly and pushed dm-4.8 and dm-4.9 again (with force, sorry about that).