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 <shaohua.li@xxxxxxxxx>
> > > > 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:
> > > > > > [<ffffffff813089f3>] ? io_schedule+0x71/0xb1
> > > > > > [<ffffffff811470be>] ? get_request_wait+0xab/0x140
> > > > > > [<ffffffff810406f4>] ? autoremove_wake_function+0x0/0x2e
> > > > > > [<ffffffff81143a4d>] ? elv_rq_merge_ok+0x89/0x97
> > > > > > [<ffffffff8114a245>] ? blk_recount_segments+0x17/0x27
> > > > > > [<ffffffff81147429>] ? __make_request+0x2d6/0x3fc
> > > > > > [<ffffffff81145b16>] ? generic_make_request+0x207/0x268
> > > > > > [<ffffffff81145c12>] ? submit_bio+0x9b/0xa2
> > > > > > [<ffffffffa01aa081>] ? btrfs_requeue_work+0xd7/0xe1
> > > > > > [btrfs]
> > > > > > [<ffffffffa01a5365>] ? run_scheduled_bios+0x297/0x48f
> > > > > > [btrfs]
> > > > > > [<ffffffffa01aa687>] ? worker_loop+0x17c/0x452 [btrfs]
> > > > > > [<ffffffffa01aa50b>] ? worker_loop+0x0/0x452 [btrfs]
> > > > > > [<ffffffff81040331>] ? kthread+0x79/0x81
> > > > > > [<ffffffff81003674>] ? kernel_thread_helper+0x4/0x10
> > > > > > [<ffffffff810402b8>] ? kthread+0x0/0x81
> > > > > > [<ffffffff81003670>] ? 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.
