From mboxrd@z Thu Jan 1 00:00:00 1970 From: Chris Mason Subject: Re: btrfs: hanging processes - race condition? Date: Mon, 14 Jun 2010 15:08:32 -0400 Message-ID: <20100614190832.GK18266@think> References: <20100611011242.GA22585@sli10-desk.sh.intel.com> <20100613065006.GA2597@sli10-desk.sh.intel.com> <20100614132829.GE18266@think> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Cc: Shaohua Li , "Yan, Zheng " , "linux-btrfs@vger.kernel.org" , "Zhang, Yanmin" , "Chen, Tim C" To: Jerome Ibanes Return-path: In-Reply-To: List-ID: On Mon, Jun 14, 2010 at 11:12:53AM -0700, Jerome Ibanes wrote: > On Mon, 14 Jun 2010, Chris Mason wrote: >=20 > >On Sun, Jun 13, 2010 at 02:50:06PM +0800, Shaohua Li wrote: > >>On Fri, Jun 11, 2010 at 10:32:07AM +0800, Yan, Zheng wrote: > >>>On Fri, Jun 11, 2010 at 9:12 AM, Shaohua Li = wrote: > >>>>On Fri, Jun 11, 2010 at 01:41:41AM +0800, Jerome Ibanes wrote: > >>>>>List, > >>>>> > >>>>>I ran into a hang issue (race condition: cpu is high when the se= rver is > >>>>>idle, meaning that btrfs is hanging, and IOwait is high as well)= running > >>>>>2.6.34 on debian/lenny on a x86_64 server (dual Opteron 275 w/ 1= 6GB ram). > >>>>>The btrfs filesystem live on 18x300GB scsi spindles, configured = as Raid-0, > >>>>>as shown below: > >>>>> > >>>>>Label: none =A0uuid: bc6442c6-2fe2-4236-a5aa-6b7841234c52 > >>>>>=A0 =A0 =A0 =A0 =A0Total devices 18 FS bytes used 2.94TB > >>>>>=A0 =A0 =A0 =A0 =A0devid =A0 =A05 size 279.39GB used 208.33GB pa= th /dev/cciss/c1d0 > >>>>>=A0 =A0 =A0 =A0 =A0devid =A0 17 size 279.39GB used 208.34GB path= /dev/cciss/c1d8 > >>>>>=A0 =A0 =A0 =A0 =A0devid =A0 16 size 279.39GB used 209.33GB path= /dev/cciss/c1d7 > >>>>>=A0 =A0 =A0 =A0 =A0devid =A0 =A04 size 279.39GB used 208.33GB pa= th /dev/cciss/c0d4 > >>>>>=A0 =A0 =A0 =A0 =A0devid =A0 =A01 size 279.39GB used 233.72GB pa= th /dev/cciss/c0d1 > >>>>>=A0 =A0 =A0 =A0 =A0devid =A0 13 size 279.39GB used 208.33GB path= /dev/cciss/c1d4 > >>>>>=A0 =A0 =A0 =A0 =A0devid =A0 =A08 size 279.39GB used 208.33GB pa= th /dev/cciss/c1d11 > >>>>>=A0 =A0 =A0 =A0 =A0devid =A0 12 size 279.39GB used 208.33GB path= /dev/cciss/c1d3 > >>>>>=A0 =A0 =A0 =A0 =A0devid =A0 =A03 size 279.39GB used 208.33GB pa= th /dev/cciss/c0d3 > >>>>>=A0 =A0 =A0 =A0 =A0devid =A0 =A09 size 279.39GB used 208.33GB pa= th /dev/cciss/c1d12 > >>>>>=A0 =A0 =A0 =A0 =A0devid =A0 =A06 size 279.39GB used 208.33GB pa= th /dev/cciss/c1d1 > >>>>>=A0 =A0 =A0 =A0 =A0devid =A0 11 size 279.39GB used 208.33GB path= /dev/cciss/c1d2 > >>>>>=A0 =A0 =A0 =A0 =A0devid =A0 14 size 279.39GB used 208.33GB path= /dev/cciss/c1d5 > >>>>>=A0 =A0 =A0 =A0 =A0devid =A0 =A02 size 279.39GB used 233.70GB pa= th /dev/cciss/c0d2 > >>>>>=A0 =A0 =A0 =A0 =A0devid =A0 15 size 279.39GB used 209.33GB path= /dev/cciss/c1d6 > >>>>>=A0 =A0 =A0 =A0 =A0devid =A0 10 size 279.39GB used 208.33GB path= /dev/cciss/c1d13 > >>>>>=A0 =A0 =A0 =A0 =A0devid =A0 =A07 size 279.39GB used 208.33GB pa= th /dev/cciss/c1d10 > >>>>>=A0 =A0 =A0 =A0 =A0devid =A0 18 size 279.39GB used 208.34GB path= /dev/cciss/c1d9 > >>>>>Btrfs v0.19-16-g075587c-dirty > >>>>> > >>>>>The filesystem, mounted in /mnt/btrfs is hanging, no existing or= new > >>>>>process can access it, however 'df' still displays the disk usag= e (3TB out > >>>>>of 5). The disks appear to be physically healthy. Please note th= at a > >>>>>significant number of files were placed on this filesystem, betw= een 20 and > >>>>>30 million files. > >>>>> > >>>>>The relevant kernel messages are displayed below: > >>>>> > >>>>>INFO: task btrfs-submit-0:4220 blocked for more than 120 seconds= =2E > >>>>>"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this= message. > >>>>>btrfs-submit- D 000000010042e12f =A0 =A0 0 =A04220 =A0 =A0 =A02 = 0x00000000 > >>>>>=A0 ffff8803e584ac70 0000000000000046 0000000000004000 000000000= 0011680 > >>>>>=A0 ffff8803f7349fd8 ffff8803f7349fd8 ffff8803e584ac70 000000000= 0011680 > >>>>>=A0 0000000000000001 ffff8803ff99d250 ffffffff8149f020 000000008= 1150ab0 > >>>>>Call Trace: > >>>>>=A0 [] ? io_schedule+0x71/0xb1 > >>>>>=A0 [] ? get_request_wait+0xab/0x140 > >>>>>=A0 [] ? autoremove_wake_function+0x0/0x2e > >>>>>=A0 [] ? elv_rq_merge_ok+0x89/0x97 > >>>>>=A0 [] ? blk_recount_segments+0x17/0x27 > >>>>>=A0 [] ? __make_request+0x2d6/0x3fc > >>>>>=A0 [] ? generic_make_request+0x207/0x268 > >>>>>=A0 [] ? submit_bio+0x9b/0xa2 > >>>>>=A0 [] ? btrfs_requeue_work+0xd7/0xe1 [btrfs] > >>>>>=A0 [] ? run_scheduled_bios+0x297/0x48f [btrfs= ] > >>>>>=A0 [] ? worker_loop+0x17c/0x452 [btrfs] > >>>>>=A0 [] ? worker_loop+0x0/0x452 [btrfs] > >>>>>=A0 [] ? kthread+0x79/0x81 > >>>>>=A0 [] ? kernel_thread_helper+0x4/0x10 > >>>>>=A0 [] ? kthread+0x0/0x81 > >>>>>=A0 [] ? kernel_thread_helper+0x0/0x10 > >>>>This looks like the issue we saw too, http://lkml.org/lkml/2010/6= /8/375. > >>>>This is reproduceable in our setup. > >>> > >>>I think I know the cause of http://lkml.org/lkml/2010/6/8/375. > >>>The code in the first do-while loop in btrfs_commit_transaction > >>>set current process to TASK_UNINTERRUPTIBLE state, then calls > >>>btrfs_start_delalloc_inodes, btrfs_wait_ordered_extents and > >>>btrfs_run_ordered_operations(). All of these function may call > >>>cond_resched(). > >>Hi, > >>When I test random write, I saw a lot of threads jump into btree_wr= itepages() > >>and do noting and io throughput is zero for some time. Looks like t= here is a > >>live lock. See the code of btree_writepages(): > >> if (wbc->sync_mode =3D=3D WB_SYNC_NONE) { > >> struct btrfs_root *root =3D BTRFS_I(mapping->host)->root; > >> u64 num_dirty; > >> unsigned long thresh =3D 32 * 1024 * 1024; > >> > >> if (wbc->for_kupdate) > >> return 0; > >> > >> /* this is a bit racy, but that's ok */ > >> num_dirty =3D root->fs_info->dirty_metadata_bytes; > >>>>>>>> if (num_dirty < thresh) > >> return 0; > >> } > >>The marked line is quite intrusive. In my test, the live lock is ca= used by the thresh > >>check. The dirty_metadata_bytes < 32M. Without it, I can't see the = live lock. Not > >>sure if this is related to the hang. > > > >How much ram do you have? The goal of the check is to avoid writing > >metadata blocks because once we write them we have to do more IO to = cow > >them again if they are changed later. >=20 > This server has 16GB of ram on a x86_64 (dual opteron 275, ecc memory= ). >=20 > >It shouldn't be looping hard in btrfs there, what was the workload? >=20 > The workload was the extraction of large tarballs (one at the time, > about 300+ files extracted by second from a single tarball, which is > pretty good), as you might expect, the disks were tested (read and > write) for physical errors before I report this bug. I think Zheng is right and this one will get fixed by the latest code. The spinning writepage part should be a different problem. -chris -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" = in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html