> On Mon, Jun 14, 2010 at 11:12:53AM -0700, Jerome Ibanes wrote: >> On Mon, 14 Jun 2010, 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 well) 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, configured as Raid-0, >>>>>>> as shown below: >>>>>>> >>>>>>> Label: none uuid: bc6442c6-2fe2-4236-a5aa-6b7841234c52 >>>>>>> Total devices 18 FS bytes used 2.94TB >>>>>>> devid 5 size 279.39GB used 208.33GB path /dev/cciss/c1d0 >>>>>>> devid 17 size 279.39GB used 208.34GB path /dev/cciss/c1d8 >>>>>>> devid 16 size 279.39GB used 209.33GB path /dev/cciss/c1d7 >>>>>>> devid 4 size 279.39GB used 208.33GB path /dev/cciss/c0d4 >>>>>>> devid 1 size 279.39GB used 233.72GB path /dev/cciss/c0d1 >>>>>>> devid 13 size 279.39GB used 208.33GB path /dev/cciss/c1d4 >>>>>>> devid 8 size 279.39GB used 208.33GB path /dev/cciss/c1d11 >>>>>>> devid 12 size 279.39GB used 208.33GB path /dev/cciss/c1d3 >>>>>>> devid 3 size 279.39GB used 208.33GB path /dev/cciss/c0d3 >>>>>>> devid 9 size 279.39GB used 208.33GB path /dev/cciss/c1d12 >>>>>>> devid 6 size 279.39GB used 208.33GB path /dev/cciss/c1d1 >>>>>>> devid 11 size 279.39GB used 208.33GB path /dev/cciss/c1d2 >>>>>>> devid 14 size 279.39GB used 208.33GB path /dev/cciss/c1d5 >>>>>>> devid 2 size 279.39GB used 233.70GB path /dev/cciss/c0d2 >>>>>>> devid 15 size 279.39GB used 209.33GB path /dev/cciss/c1d6 >>>>>>> devid 10 size 279.39GB used 208.33GB path /dev/cciss/c1d13 >>>>>>> devid 7 size 279.39GB used 208.33GB path /dev/cciss/c1d10 >>>>>>> devid 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 usage (3TB out >>>>>>> of 5). The disks appear to be physically healthy. Please note that a >>>>>>> significant number of files were placed on this filesystem, between 20 and >>>>>>> 30 million files. >>>>>>> >>>>>>> The relevant kernel messages are displayed below: >>>>>>> >>>>>>> INFO: task btrfs-submit-0:4220 blocked for more than 120 seconds. >>>>>>> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. >>>>>>> btrfs-submit- D 000000010042e12f 0 4220 2 0x00000000 >>>>>>> ffff8803e584ac70 0000000000000046 0000000000004000 0000000000011680 >>>>>>> ffff8803f7349fd8 ffff8803f7349fd8 ffff8803e584ac70 0000000000011680 >>>>>>> 0000000000000001 ffff8803ff99d250 ffffffff8149f020 0000000081150ab0 >>>>>>> Call Trace: >>>>>>> [] ? io_schedule+0x71/0xb1 >>>>>>> [] ? get_request_wait+0xab/0x140 >>>>>>> [] ? autoremove_wake_function+0x0/0x2e >>>>>>> [] ? elv_rq_merge_ok+0x89/0x97 >>>>>>> [] ? blk_recount_segments+0x17/0x27 >>>>>>> [] ? __make_request+0x2d6/0x3fc >>>>>>> [] ? generic_make_request+0x207/0x268 >>>>>>> [] ? submit_bio+0x9b/0xa2 >>>>>>> [] ? btrfs_requeue_work+0xd7/0xe1 [btrfs] >>>>>>> [] ? run_scheduled_bios+0x297/0x48f [btrfs] >>>>>>> [] ? worker_loop+0x17c/0x452 [btrfs] >>>>>>> [] ? worker_loop+0x0/0x452 [btrfs] >>>>>>> [] ? kthread+0x79/0x81 >>>>>>> [] ? kernel_thread_helper+0x4/0x10 >>>>>>> [] ? kthread+0x0/0x81 >>>>>>> [] ? 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_writepages() >>>> and do noting and io throughput is zero for some time. Looks like there is a >>>> live lock. See the code of btree_writepages(): >>>> if (wbc->sync_mode == WB_SYNC_NONE) { >>>> struct btrfs_root *root = BTRFS_I(mapping->host)->root; >>>> u64 num_dirty; >>>> unsigned long thresh = 32 * 1024 * 1024; >>>> >>>> if (wbc->for_kupdate) >>>> return 0; >>>> >>>> /* this is a bit racy, but that's ok */ >>>> num_dirty = 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 caused 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. >> >> This server has 16GB of ram on a x86_64 (dual opteron 275, ecc memory). >> >>> It shouldn't be looping hard in btrfs there, what was the workload? >> >> 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. I'm trying to repro with 2.6.35-rc3, expect results within 24 hours. Jerome J. Ibanes