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Date: Tue, 3 Jul 2012 13:01:43 +0800 From: Fengguang Wu <fengguang.wu@...el.com> To: Prasad Koya <prasad.koya@...il.com> Cc: jack@...e.cz, LKML <linux-kernel@...r.kernel.org> Subject: Re: sync blocked for long time On Mon, Jul 02, 2012 at 09:54:59PM -0700, Prasad Koya wrote: > We have 'noop' as elevator. Tried other elevators too but didn't make any > difference. Can the amount of buffers (some x KB or MB) to be synced tuned? Yes, it's worthwhile to lower the number of dirty pages. echo 5 > /proc/sys/vm/dirty_ratio Or specifically tune the USB key's share of dirty pages: echo 10 > /sys/block/sda/bdi/max_ratio Please replace 'sda' with your USB device name. Thanks, Fengguang > On Mon, Jul 2, 2012 at 9:34 PM, Fengguang Wu <fengguang.wu@...el.com> wrote: > > > On Mon, Jul 02, 2012 at 09:10:45PM -0700, Prasad Koya wrote: > > > Sorry for missing that important info. Its vfat on both USBs. 2.6.32 is > > our > > > current production kernel and we have hung_task_panic as 1 to detect any > > > > To detect the blocked tasks, /proc/sys/kernel/hung_task_warnings > > should be enough. Then you get the warning in dmesg, and can have a > > dmesg monitor script to grep for 'task .* blocked for more than .* > > seconds'. > > > > > such tasks. While trying to reproduce below issue I ran into bottom one. > > > Both of them seem to be related to syncing dirty buffers to storage. > > > > It seems being blocked in __bread_slow() waiting for the READ to complete. > > I can imagine the READ be delayed by the lots of SYNC writes, however > > 120 seconds still look way too long.. > > > > Thanks, > > Fengguang > > > > > <3>[12099840.577044] INFO: task cli_copy:27939 blocked for more than > > > 120 seconds. > > > <3>[12099840.655175] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" > > > disables this message. > > > <6>[12099840.751981] Cli D ffff8800036101c0 0 27939 27567 > > > 0x00020004 > > > <4>[12099840.751988] ffff8800359a3678 0000000000200082 0000000000000000 > > > 0000000000000000 > > > <4>[12099840.751995] ffff8800359a35d8 ffffffff8130e312 ffff8800359a35d8 > > > ffff8800359a3fd8 > > > <4>[12099840.752002] ffff88003e93c2c8 000000000000ca08 00000000000101c0 > > > 00000000000101c0 > > > <4>[12099840.752008] Call Trace: > > > <4>[12099840.752019] [<ffffffff8130e312>] ? _spin_lock_irq+0x1f/0x23 > > > <4>[12099840.752028] [<ffffffff810ae0cc>] ? sync_buffer+0x0/0x42 > > > <4>[12099840.752033] [<ffffffff810ae0cc>] ? sync_buffer+0x0/0x42 > > > <4>[12099840.752038] [<ffffffff8130c22e>] io_schedule+0x38/0x4d > > > <4>[12099840.752042] [<ffffffff810ae10a>] sync_buffer+0x3e/0x42 > > > <4>[12099840.752047] [<ffffffff8130c6c1>] __wait_on_bit+0x43/0x76 > > > <4>[12099840.752051] [<ffffffff8130c75d>] > > out_of_line_wait_on_bit+0x69/0x74 > > > <4>[12099840.752056] [<ffffffff810ae0cc>] ? sync_buffer+0x0/0x42 > > > <4>[12099840.752063] [<ffffffff81047f11>] ? wake_bit_function+0x0/0x2e > > > <4>[12099840.752068] [<ffffffff810ae05b>] __wait_on_buffer+0x1f/0x21 > > > <4>[12099840.752073] [<ffffffff810b0568>] __bread+0x95/0xad > > > <4>[12099840.752079] [<ffffffff81113b1f>] fat_ent_bread+0x6a/0xab > > > <4>[12099840.752084] [<ffffffff8111320b>] fat_alloc_clusters+0x1fb/0x46c > > > <4>[12099840.752092] [<ffffffff81115e57>] fat_get_block+0x103/0x1da > > > <4>[12099840.752097] [<ffffffff8130e1f8>] ? _spin_unlock+0x13/0x2e > > > <4>[12099840.752102] [<ffffffff810aeded>] > > __block_prepare_write+0x1b3/0x3b6 > > > <4>[12099840.752107] [<ffffffff81115d54>] ? fat_get_block+0x0/0x1da > > > <4>[12099840.752113] [<ffffffff81067b18>] ? > > > grab_cache_page_write_begin+0x7e/0xaa > > > <4>[12099840.752119] [<ffffffff810af17e>] block_write_begin+0x7b/0xcd > > > <4>[12099840.752124] [<ffffffff810af4e9>] cont_write_begin+0x319/0x33d > > > <4>[12099840.752129] [<ffffffff81115d54>] ? fat_get_block+0x0/0x1da > > > <4>[12099840.752135] [<ffffffff81116026>] fat_write_begin+0x31/0x33 > > > <4>[12099840.752139] [<ffffffff81115d54>] ? fat_get_block+0x0/0x1da > > > <4>[12099840.752144] [<ffffffff810684d0>] > > > generic_file_buffered_write+0x107/0x2a1 > > > <4>[12099840.752151] [<ffffffff810394da>] ? current_fs_time+0x22/0x29 > > > <4>[12099840.752156] [<ffffffff81068b25>] > > __generic_file_aio_write+0x350/0x385 > > > <4>[12099840.752161] [<ffffffff8130cbec>] ? > > __mutex_lock_slowpath+0x26c/0x294 > > > <4>[12099840.752167] [<ffffffff81068bb8>] > > generic_file_aio_write+0x5e/0xa8 > > > <4>[12099840.752173] [<ffffffff8108d05a>] do_sync_write+0xe3/0x120 > > > <4>[12099840.752178] [<ffffffff81047edd>] ? > > autoremove_wake_function+0x0/0x34 > > > <4>[12099840.752185] [<ffffffff81080afd>] ? do_mmap_pgoff+0x28b/0x2ee > > > <4>[12099840.752190] [<ffffffff8108d9cb>] vfs_write+0xad/0x14e > > > <4>[12099840.752195] [<ffffffff8108e25b>] ? fget_light+0xae/0xd2 > > > <4>[12099840.752200] [<ffffffff8108db25>] sys_write+0x45/0x6c > > > <4>[12099840.752206] [<ffffffff810260c5>] cstar_dispatch+0x7/0x2b > > > > > > > > > On Mon, Jul 2, 2012 at 8:49 PM, Fengguang Wu <fengguang.wu@...el.com> > > wrote: > > > > > > > Hi Prasad, > > > > > > > > On Mon, Jul 02, 2012 at 08:37:19PM -0700, Prasad Koya wrote: > > > > > Hi > > > > > > > > > > Sorry about writing to your personal address. I'm running into below > > > > panic > > > > > but I couldn't find any patch for this in 2.6.32. I do see below > > > > discussion > > > > > related to pretty much similar issue which doesn't appear to be > > > > resolved. I > > > > > looked around quite a bit but I couldn't find any patches for this. > > Is > > > > this > > > > > still unresolved? I have 2 USB sticks and I can get into this state > > by > > > > > copying 2 large files (say 200-300M each) simultaneously (followed by > > > > sync) > > > > > into both drives. > > > > > > > > That is doing sync lots of data on slow device, with the sync time > > > > being further enlarged by the active writers. I can imagine for the > > > > sync to take very long time. > > > > > > > > What's the filesystem btw? > > > > > > > > > Appreciate any pointers. > > > > > > > > > > thank you. > > > > > > > > > > http://marc.info/?t=126596633700002&r=1&w=2 > > > > > > > > > > > > > > > <3>[ 600.392088] INFO: task sync:2675 blocked for more than 120 > > seconds. > > > > > <3>[ 600.466884] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" > > > > > disables this message. > > > > ... > > > > > <4>[ 600.560507] [<ffffffff810a7dab>] sync_inodes_sb+0x1d/0xf1 > > > > > <4>[ 600.560519] [<ffffffff810abb3e>] __sync_filesystem+0x29/0x52 > > > > > <4>[ 600.560536] [<ffffffff810abc0f>] sync_filesystems+0xa8/0xfe > > > > > <4>[ 600.560556] [<ffffffff810abcb5>] sys_sync+0x1c/0x2e > > > > > <4>[ 600.560570] [<ffffffff810260c5>] cstar_dispatch+0x7/0x2b > > > > > <0>[ 600.560580] Kernel panic - not syncing: hung_task: blocked > > tasks > > > > > > > > Please check /proc/sys/kernel/hung_task_panic . Normal users should > > > > never set it to 1.. > > > > > > > > Thanks, > > > > Fengguang > > > > > > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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