From mboxrd@z Thu Jan 1 00:00:00 1970 From: Shaohua Li Subject: Re: btrfs: hanging processes - race condition? Date: Thu, 17 Jun 2010 09:41:18 +0800 Message-ID: <20100617014118.GA21213@sli10-desk.sh.intel.com> 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 To: Chris Mason , "Yan, Zheng " , Jerome Ibanes , "linux-btrfs@vger.kernel.org" , "Zhang, Y Return-path: In-Reply-To: <20100614132829.GE18266@think> List-ID: On Mon, Jun 14, 2010 at 09:28:29PM +0800, Chris Mason wrote: > 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 = server is > > > >> idle, meaning that btrfs is hanging, and IOwait is high as wel= l) running > > > >> 2.6.34 on debian/lenny on a x86_64 server (dual Opteron 275 w/= 16GB ram). > > > >> The btrfs filesystem live on 18x300GB scsi spindles, configure= d 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 = path /dev/cciss/c1d0 > > > >> =A0 =A0 =A0 =A0 =A0devid =A0 17 size 279.39GB used 208.34GB pa= th /dev/cciss/c1d8 > > > >> =A0 =A0 =A0 =A0 =A0devid =A0 16 size 279.39GB used 209.33GB pa= th /dev/cciss/c1d7 > > > >> =A0 =A0 =A0 =A0 =A0devid =A0 =A04 size 279.39GB used 208.33GB = path /dev/cciss/c0d4 > > > >> =A0 =A0 =A0 =A0 =A0devid =A0 =A01 size 279.39GB used 233.72GB = path /dev/cciss/c0d1 > > > >> =A0 =A0 =A0 =A0 =A0devid =A0 13 size 279.39GB used 208.33GB pa= th /dev/cciss/c1d4 > > > >> =A0 =A0 =A0 =A0 =A0devid =A0 =A08 size 279.39GB used 208.33GB = path /dev/cciss/c1d11 > > > >> =A0 =A0 =A0 =A0 =A0devid =A0 12 size 279.39GB used 208.33GB pa= th /dev/cciss/c1d3 > > > >> =A0 =A0 =A0 =A0 =A0devid =A0 =A03 size 279.39GB used 208.33GB = path /dev/cciss/c0d3 > > > >> =A0 =A0 =A0 =A0 =A0devid =A0 =A09 size 279.39GB used 208.33GB = path /dev/cciss/c1d12 > > > >> =A0 =A0 =A0 =A0 =A0devid =A0 =A06 size 279.39GB used 208.33GB = path /dev/cciss/c1d1 > > > >> =A0 =A0 =A0 =A0 =A0devid =A0 11 size 279.39GB used 208.33GB pa= th /dev/cciss/c1d2 > > > >> =A0 =A0 =A0 =A0 =A0devid =A0 14 size 279.39GB used 208.33GB pa= th /dev/cciss/c1d5 > > > >> =A0 =A0 =A0 =A0 =A0devid =A0 =A02 size 279.39GB used 233.70GB = path /dev/cciss/c0d2 > > > >> =A0 =A0 =A0 =A0 =A0devid =A0 15 size 279.39GB used 209.33GB pa= th /dev/cciss/c1d6 > > > >> =A0 =A0 =A0 =A0 =A0devid =A0 10 size 279.39GB used 208.33GB pa= th /dev/cciss/c1d13 > > > >> =A0 =A0 =A0 =A0 =A0devid =A0 =A07 size 279.39GB used 208.33GB = path /dev/cciss/c1d10 > > > >> =A0 =A0 =A0 =A0 =A0devid =A0 18 size 279.39GB used 208.34GB pa= th /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 us= age (3TB out > > > >> of 5). The disks appear to be physically healthy. Please note = that a > > > >> significant number of files were placed on this filesystem, be= tween 20 and > > > >> 30 million files. > > > >> > > > >> The relevant kernel messages are displayed below: > > > >> > > > >> INFO: task btrfs-submit-0:4220 blocked for more than 120 secon= ds. > > > >> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables th= is message. > > > >> btrfs-submit- D 000000010042e12f =A0 =A0 0 =A04220 =A0 =A0 =A0= 2 0x00000000 > > > >> =A0 ffff8803e584ac70 0000000000000046 0000000000004000 0000000= 000011680 > > > >> =A0 ffff8803f7349fd8 ffff8803f7349fd8 ffff8803e584ac70 0000000= 000011680 > > > >> =A0 0000000000000001 ffff8803ff99d250 ffffffff8149f020 0000000= 081150ab0 > > > >> 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 [btr= fs] > > > >> =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. > > >=20 > > > 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; > >=20 > > if (wbc->for_kupdate) > > return 0; > >=20 > > /* 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. >=20 > 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 c= ow > them again if they are changed later. >=20 > It shouldn't be looping hard in btrfs there, what was the workload? This is a fio randomwrite. Yep, I limited memory to a small size (~500M= ), because it makes me easily to produce a 'xxx blocked for more than 120 seconds' issue. I= can understand small memory could be an issue, but this still looks intrusive, right? The issue Yanmin reported is under 2.6.35-rc1, so might not be the 'TASK_UNINTERRUPTIBLE' issue, but we will try -rc3 too. Thanks, Shaohua -- 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