Dear Neil,

We are facing IO struck issue with raid5  in the following scenario. (please see the attachment for the complete information)
In RAID5 array, if a drive is removed while initialization and the same time if IO is happening to that md. Then IO is getting struck, and md_raid5 thread is using 100 % of CPU. Also the md state showing as resync=PENDING

Kernel :  Issue found in the following kernels
RHEL 6.5 (2.6.32-431.el6.x86_64)
CentOS 7 (kernel-3.10.0-123.13.1.el7.x86_64)

Steps to Reproduce the issue:

1. Created a raid 5 md with 4 drives using the below mdadm command.
mdadm -C /dev/md0 -c 64 -l 5 -f -n 4 -e 1.2 /dev/sdb6 /dev/sdc6 /dev/sdd6 /dev/sde6

2. Make the md writable
mdadm –readwrite /dev/md0

3. Now md will start initialization

4. Run FIO Tool, the the below said configuration
/usr/bin/fio --name=md0 --filename=/dev/md0 --thread --numjobs=10 --direct=1 --group_reporting --unlink=0 --loops=1 --offset=0 --randrepeat=1 --norandommap --scramble_buffers=1 --stonewall --ioengine=libaio --rw=randwrite --bs=8704 --iodepth=4000 --runtime=3000 --blockalign=512

4. During MD initialzing, remove a drive(either using MDADM set faulty/remove or remove manually)

5. Now the IO will struck, and cat /proc/mdstat shows states with resync=PENDING
---------------------------------------------------------------------------------------------
top - output show, md_raid5 using 100% cpu

top - 17:55:06 up  1:09,  3 users,  load average: 11.98, 8.53, 3.99
PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
2690 root      20   0     0    0    0 R 100.0  0.0   6:44.41 md0_raid5
---------------------------------------------------------------------------------------------
dmesg - show the stack trace

INFO: task fio:2715 blocked for more than 120 seconds.
Not tainted 2.6.32-431.el6.x86_64 #1
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
fio           D 000000000000000a     0  2715   2654 0x00000080
ffff88043b623598 0000000000000082 0000000000000000 ffffffff81058d53
ffff88043b623548 ffff880230e49cc0 ffff8802389aa228 ffff88043b2ad1b8
ffff88043b40b098 ffff88043b623fd8 000000000000fbc8 ffff88043b40b098
Call Trace:
[<ffffffff81058d53>] ? __wake_up+0x53/0x70
[<ffffffffa0304146>] get_active_stripe+0x236/0x830 [raid456]
[<ffffffff81065df0>] ? default_wake_function+0x0/0x20
[<ffffffff8109b5ce>] ? prepare_to_wait+0x4e/0x80
[<ffffffffa0308e15>] make_request+0x1b5/0xc6c [raid456]
[<ffffffff8109b2a0>] ? autoremove_wake_function+0x0/0x40
[<ffffffff8140fa39>] ? md_wakeup_thread+0x39/0x70
[<ffffffff81415b41>] md_make_request+0xe1/0x230
[<ffffffffa0308f66>] ? make_request+0x306/0xc6c [raid456]
[<ffffffff81266c50>] generic_make_request+0x240/0x5a0
[<ffffffff811220e5>] ? mempool_alloc_slab+0x15/0x20
[<ffffffff81122283>] ? mempool_alloc+0x63/0x140
[<ffffffff81267020>] submit_bio+0x70/0x120
[<ffffffff811c767a>] do_direct_IO+0x7ca/0xfa0
[<ffffffff811c8196>] __blockdev_direct_IO_newtrunc+0x346/0x1270
[<ffffffff811c4330>] ? blkdev_get_block+0x0/0x20
[<ffffffff811c9137>] __blockdev_direct_IO+0x77/0xe0
[<ffffffff811c4330>] ? blkdev_get_block+0x0/0x20
[<ffffffff811c53b7>] blkdev_direct_IO+0x57/0x60
[<ffffffff811c4330>] ? blkdev_get_block+0x0/0x20
[<ffffffff81120552>] generic_file_direct_write+0xc2/0x190
[<ffffffff81121e71>] __generic_file_aio_write+0x3a1/0x490
[<ffffffff811d64c0>] ? aio_read_evt+0xa0/0x170
[<ffffffff811c490c>] blkdev_aio_write+0x3c/0xa0
[<ffffffff811c48d0>] ? blkdev_aio_write+0x0/0xa0
[<ffffffff811d4f64>] aio_rw_vect_retry+0x84/0x200
[<ffffffff811d6924>] aio_run_iocb+0x64/0x170
[<ffffffff811d7d51>] do_io_submit+0x291/0x920
[<ffffffff811d83f0>] sys_io_submit+0x10/0x20
[<ffffffff8100b072>] system_call_fastpath+0x16/0x1b
INFO: task fio:2717 blocked for more than 120 seconds.
Not tainted 2.6.32-431.el6.x86_64 #1
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
fio           D 0000000000000004     0  2717   2654 0x00000080
ffff880439e97698 0000000000000082 ffff880439e97628 ffffffff81058d53
ffff880439e97648 ffff880230e49cc0 ffff8802389aa228 ffff88043b2ad1b8
ffff88043b0adab8 ffff880439e97fd8 000000000000fbc8 ffff88043b0adab8
Call Trace:
[<ffffffff81058d53>] ? __wake_up+0x53/0x70
[<ffffffffa030334b>] ? md_raid5_unplug_device+0x7b/0x100 [raid456]
[<ffffffffa0304146>] get_active_stripe+0x236/0x830 [raid456]
[<ffffffff81065df0>] ? default_wake_function+0x0/0x20
[<ffffffff8109b5ce>] ? prepare_to_wait+0x4e/0x80
[<ffffffffa0308e15>] make_request+0x1b5/0xc6c [raid456]
[<ffffffff8109b2a0>] ? autoremove_wake_function+0x0/0x40
[<ffffffff811220e5>] ? mempool_alloc_slab+0x15/0x20
[<ffffffff81415b41>] md_make_request+0xe1/0x230
[<ffffffff811c32f0>] ? __bio_add_page+0x110/0x230
[<ffffffff81266c50>] generic_make_request+0x240/0x5a0
[<ffffffff811c742c>] ? do_direct_IO+0x57c/0xfa0
[<ffffffff81267020>] submit_bio+0x70/0x120
[<ffffffff811c8e50>] __blockdev_direct_IO_newtrunc+0x1000/0x1270
[<ffffffff811c4330>] ? blkdev_get_block+0x0/0x20
[<ffffffff811c9137>] __blockdev_direct_IO+0x77/0xe0
[<ffffffff811c4330>] ? blkdev_get_block+0x0/0x20
[<ffffffff811c53b7>] blkdev_direct_IO+0x57/0x60
[<ffffffff811c4330>] ? blkdev_get_block+0x0/0x20
[<ffffffff81120552>] generic_file_direct_write+0xc2/0x190
[<ffffffff81121e71>] __generic_file_aio_write+0x3a1/0x490
[<ffffffff811d64c0>] ? aio_read_evt+0xa0/0x170
[<ffffffff811c490c>] blkdev_aio_write+0x3c/0xa0
[<ffffffff811c48d0>] ? blkdev_aio_write+0x0/0xa0
[<ffffffff811d4f64>] aio_rw_vect_retry+0x84/0x200
[<ffffffff811d6924>] aio_run_iocb+0x64/0x170
[<ffffffff811d7d51>] do_io_submit+0x291/0x920
[<ffffffff811d83f0>] sys_io_submit+0x10/0x20
[<ffffffff8100b072>] system_call_fastpath+0x16/0x1b
INFO: task fio:2718 blocked for more than 120 seconds.
Not tainted 2.6.32-431.el6.x86_64 #1
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
fio           D 0000000000000005     0  2718   2654 0x00000080
ffff88043bc13698 0000000000000082 ffff88043bc13628 ffffffff81058d53
ffff88043bc13648 ffff880230e49cc0 ffff8802389aa228 ffff88043b2ad1b8
ffff88043b0ad058 ffff88043bc13fd8 000000000000fbc8 ffff88043b0ad058
Call Trace:
[<ffffffff81058d53>] ? __wake_up+0x53/0x70
[<ffffffffa030334b>] ? md_raid5_unplug_device+0x7b/0x100 [raid456]
[<ffffffffa0304146>] get_active_stripe+0x236/0x830 [raid456]
[<ffffffff81065df0>] ? default_wake_function+0x0/0x20
[<ffffffff8109b5ce>] ? prepare_to_wait+0x4e/0x80
[<ffffffffa0308e15>] make_request+0x1b5/0xc6c [raid456]
[<ffffffff8109b2a0>] ? autoremove_wake_function+0x0/0x40
[<ffffffff811220e5>] ? mempool_alloc_slab+0x15/0x20
[<ffffffff81415b41>] md_make_request+0xe1/0x230
[<ffffffff811c3fd2>] ? bvec_alloc_bs+0x62/0x110
[<ffffffff811c32f0>] ? __bio_add_page+0x110/0x230
[<ffffffff81266c50>] generic_make_request+0x240/0x5a0
[<ffffffff811c742c>] ? do_direct_IO+0x57c/0xfa0
[<ffffffff81267020>] submit_bio+0x70/0x120
[<ffffffff811c8e50>] __blockdev_direct_IO_newtrunc+0x1000/0x1270
[<ffffffff811c4330>] ? blkdev_get_block+0x0/0x20
[<ffffffff811c9137>] __blockdev_direct_IO+0x77/0xe0
[<ffffffff811c4330>] ? blkdev_get_block+0x0/0x20
[<ffffffff811c53b7>] blkdev_direct_IO+0x57/0x60
[<ffffffff811c4330>] ? blkdev_get_block+0x0/0x20
[<ffffffff81120552>] generic_file_direct_write+0xc2/0x190
[<ffffffff81121e71>] __generic_file_aio_write+0x3a1/0x490
[<ffffffff811d64c0>] ? aio_read_evt+0xa0/0x170
[<ffffffff811c490c>] blkdev_aio_write+0x3c/0xa0
[<ffffffff811c48d0>] ? blkdev_aio_write+0x0/0xa0
[<ffffffff811d4f64>] aio_rw_vect_retry+0x84/0x200
[<ffffffff811d6924>] aio_run_iocb+0x64/0x170
[<ffffffff811d7d51>] do_io_submit+0x291/0x920
[<ffffffff811d83f0>] sys_io_submit+0x10/0x20
[<ffffffff8100b072>] system_call_fastpath+0x16/0x1b
INFO: task fio:2719 blocked for more than 120 seconds.
Not tainted 2.6.32-431.el6.x86_64 #1
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
fio           D 0000000000000001     0  2719   2654 0x00000080
ffff880439ebb698 0000000000000082 ffff880439ebb628 ffffffff81058d53
ffff880439ebb648 ffff880230e49cc0 ffff8802389aa228 ffff88043b2ad1b8
ffff88043b0ac5f8 ffff880439ebbfd8 000000000000fbc8 ffff88043b0ac5f8
Call Trace:
[<ffffffff81058d53>] ? __wake_up+0x53/0x70
[<ffffffffa030334b>] ? md_raid5_unplug_device+0x7b/0x100 [raid456]
[<ffffffffa0304146>] get_active_stripe+0x236/0x830 [raid456]
[<ffffffff81065df0>] ? default_wake_function+0x0/0x20
[<ffffffff8109b5ce>] ? prepare_to_wait+0x4e/0x80
[<ffffffffa0308e15>] make_request+0x1b5/0xc6c [raid456]
[<ffffffff8109b2a0>] ? autoremove_wake_function+0x0/0x40
[<ffffffff811220e5>] ? mempool_alloc_slab+0x15/0x20
[<ffffffff81415b41>] md_make_request+0xe1/0x230
[<ffffffff811c3fd2>] ? bvec_alloc_bs+0x62/0x110
[<ffffffff811c32f0>] ? __bio_add_page+0x110/0x230
[<ffffffff81266c50>] generic_make_request+0x240/0x5a0
[<ffffffff811c742c>] ? do_direct_IO+0x57c/0xfa0
[<ffffffff81267020>] submit_bio+0x70/0x120
[<ffffffff811c8acd>] __blockdev_direct_IO_newtrunc+0xc7d/0x1270
[<ffffffff811c4330>] ? blkdev_get_block+0x0/0x20
[<ffffffff811c9137>] __blockdev_direct_IO+0x77/0xe0
[<ffffffff811c4330>] ? blkdev_get_block+0x0/0x20
[<ffffffff811c53b7>] blkdev_direct_IO+0x57/0x60
[<ffffffff811c4330>] ? blkdev_get_block+0x0/0x20
[<ffffffff81120552>] generic_file_direct_write+0xc2/0x190
[<ffffffff81121e71>] __generic_file_aio_write+0x3a1/0x490
[<ffffffff811d64c0>] ? aio_read_evt+0xa0/0x170
[<ffffffff811c490c>] blkdev_aio_write+0x3c/0xa0
[<ffffffff811c48d0>] ? blkdev_aio_write+0x0/0xa0
[<ffffffff811d4f64>] aio_rw_vect_retry+0x84/0x200
[<ffffffff811d6924>] aio_run_iocb+0x64/0x170
[<ffffffff811d7d51>] do_io_submit+0x291/0x920
[<ffffffff811d83f0>] sys_io_submit+0x10/0x20
[<ffffffff8100b072>] system_call_fastpath+0x16/0x1b
INFO: task fio:2720 blocked for more than 120 seconds.
Not tainted 2.6.32-431.el6.x86_64 #1
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
fio           D 0000000000000008     0  2720   2654 0x00000080
ffff88043b8cf698 0000000000000082 ffff88043b8cf628 ffffffff81058d53
ffff88043b8cf648 ffff880230e49cc0 ffff8802389aa228 ffff88043b2ad1b8
ffff880439e89af8 ffff88043b8cffd8 000000000000fbc8 ffff880439e89af8
Call Trace:
[<ffffffff81058d53>] ? __wake_up+0x53/0x70
[<ffffffffa030334b>] ? md_raid5_unplug_device+0x7b/0x100 [raid456]
[<ffffffffa0304146>] get_active_stripe+0x236/0x830 [raid456]
[<ffffffff81065df0>] ? default_wake_function+0x0/0x20
[<ffffffff8109b5ce>] ? prepare_to_wait+0x4e/0x80
[<ffffffffa0308e15>] make_request+0x1b5/0xc6c [raid456]
[<ffffffff8109b2a0>] ? autoremove_wake_function+0x0/0x40
[<ffffffff811220e5>] ? mempool_alloc_slab+0x15/0x20
[<ffffffff81415b41>] md_make_request+0xe1/0x230
[<ffffffff811c3fd2>] ? bvec_alloc_bs+0x62/0x110
[<ffffffff811c32f0>] ? __bio_add_page+0x110/0x230
[<ffffffff81266c50>] generic_make_request+0x240/0x5a0
[<ffffffff811c742c>] ? do_direct_IO+0x57c/0xfa0
[<ffffffff81267020>] submit_bio+0x70/0x120
[<ffffffff811c8acd>] __blockdev_direct_IO_newtrunc+0xc7d/0x1270
[<ffffffff811c4330>] ? blkdev_get_block+0x0/0x20
[<ffffffff811c9137>] __blockdev_direct_IO+0x77/0xe0
[<ffffffff811c4330>] ? blkdev_get_block+0x0/0x20
[<ffffffff811c53b7>] blkdev_direct_IO+0x57/0x60
[<ffffffff811c4330>] ? blkdev_get_block+0x0/0x20
[<ffffffff81120552>] generic_file_direct_write+0xc2/0x190
[<ffffffff81121e71>] __generic_file_aio_write+0x3a1/0x490
[<ffffffff811d64c0>] ? aio_read_evt+0xa0/0x170
[<ffffffff811c490c>] blkdev_aio_write+0x3c/0xa0
[<ffffffff811c48d0>] ? blkdev_aio_write+0x0/0xa0
[<ffffffff811d4f64>] aio_rw_vect_retry+0x84/0x200
[<ffffffff811d6924>] aio_run_iocb+0x64/0x170
[<ffffffff811d7d51>] do_io_submit+0x291/0x920
[<ffffffff811d83f0>] sys_io_submit+0x10/0x20
[<ffffffff8100b072>] system_call_fastpath+0x16/0x1b
INFO: task fio:2721 blocked for more than 120 seconds.
Not tainted 2.6.32-431.el6.x86_64 #1
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
fio           D 0000000000000000     0  2721   2654 0x00000080
ffff88043b047698 0000000000000082 ffff88043b047628 ffffffff81058d53
ffff88043b047648 ffff880230e49cc0 ffff8802389aa228 ffff88043b2ad1b8
ffff880439e89098 ffff88043b047fd8 000000000000fbc8 ffff880439e89098
Call Trace:
[<ffffffff81058d53>] ? __wake_up+0x53/0x70
[<ffffffffa030334b>] ? md_raid5_unplug_device+0x7b/0x100 [raid456]
[<ffffffffa0304146>] get_active_stripe+0x236/0x830 [raid456]
[<ffffffff81065df0>] ? default_wake_function+0x0/0x20
[<ffffffff8109b5ce>] ? prepare_to_wait+0x4e/0x80
[<ffffffffa0308e15>] make_request+0x1b5/0xc6c [raid456]
[<ffffffff8109b2a0>] ? autoremove_wake_function+0x0/0x40
[<ffffffff811220e5>] ? mempool_alloc_slab+0x15/0x20
[<ffffffff81415b41>] md_make_request+0xe1/0x230
[<ffffffff811c3fd2>] ? bvec_alloc_bs+0x62/0x110
[<ffffffff811c32f0>] ? __bio_add_page+0x110/0x230
[<ffffffff81266c50>] generic_make_request+0x240/0x5a0
[<ffffffff811c742c>] ? do_direct_IO+0x57c/0xfa0
[<ffffffff81267020>] submit_bio+0x70/0x120
[<ffffffff811c8acd>] __blockdev_direct_IO_newtrunc+0xc7d/0x1270
[<ffffffff811c4330>] ? blkdev_get_block+0x0/0x20
[<ffffffff811c9137>] __blockdev_direct_IO+0x77/0xe0
[<ffffffff811c4330>] ? blkdev_get_block+0x0/0x20
[<ffffffff811c53b7>] blkdev_direct_IO+0x57/0x60
[<ffffffff811c4330>] ? blkdev_get_block+0x0/0x20
[<ffffffff81120552>] generic_file_direct_write+0xc2/0x190
[<ffffffff81121e71>] __generic_file_aio_write+0x3a1/0x490
[<ffffffff811d64c0>] ? aio_read_evt+0xa0/0x170
[<ffffffff811c490c>] blkdev_aio_write+0x3c/0xa0
[<ffffffff811c48d0>] ? blkdev_aio_write+0x0/0xa0
[<ffffffff811d4f64>] aio_rw_vect_retry+0x84/0x200
[<ffffffff811d6924>] aio_run_iocb+0x64/0x170
[<ffffffff811d7d51>] do_io_submit+0x291/0x920
[<ffffffff811d83f0>] sys_io_submit+0x10/0x20
[<ffffffff8100b072>] system_call_fastpath+0x16/0x1b
INFO: task fio:2722 blocked for more than 120 seconds.
Not tainted 2.6.32-431.el6.x86_64 #1
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
fio           D 0000000000000000     0  2722   2654 0x00000080
ffff880439ea3698 0000000000000082 ffff880439ea3628 ffffffff81058d53
ffff880439ea3648 ffff880230e49cc0 ffff8802389aa228 ffff88043b2ad1b8
ffff880439e88638 ffff880439ea3fd8 000000000000fbc8 ffff880439e88638
Call Trace:
[<ffffffff81058d53>] ? __wake_up+0x53/0x70
[<ffffffffa030334b>] ? md_raid5_unplug_device+0x7b/0x100 [raid456]
[<ffffffffa0304146>] get_active_stripe+0x236/0x830 [raid456]
[<ffffffff81065df0>] ? default_wake_function+0x0/0x20
[<ffffffff8109b5ce>] ? prepare_to_wait+0x4e/0x80
[<ffffffffa0308e15>] make_request+0x1b5/0xc6c [raid456]
[<ffffffff8109b2a0>] ? autoremove_wake_function+0x0/0x40
[<ffffffff811220e5>] ? mempool_alloc_slab+0x15/0x20
[<ffffffff81415b41>] md_make_request+0xe1/0x230
[<ffffffff811c3fd2>] ? bvec_alloc_bs+0x62/0x110
[<ffffffff811c32f0>] ? __bio_add_page+0x110/0x230
[<ffffffff81266c50>] generic_make_request+0x240/0x5a0
[<ffffffff811c742c>] ? do_direct_IO+0x57c/0xfa0
[<ffffffff81267020>] submit_bio+0x70/0x120
[<ffffffff811c8acd>] __blockdev_direct_IO_newtrunc+0xc7d/0x1270
[<ffffffff811c4330>] ? blkdev_get_block+0x0/0x20
[<ffffffff811c9137>] __blockdev_direct_IO+0x77/0xe0
[<ffffffff811c4330>] ? blkdev_get_block+0x0/0x20
[<ffffffff811c53b7>] blkdev_direct_IO+0x57/0x60
[<ffffffff811c4330>] ? blkdev_get_block+0x0/0x20
[<ffffffff81120552>] generic_file_direct_write+0xc2/0x190
[<ffffffff81121e71>] __generic_file_aio_write+0x3a1/0x490
[<ffffffff811d64c0>] ? aio_read_evt+0xa0/0x170
[<ffffffff811c490c>] blkdev_aio_write+0x3c/0xa0
[<ffffffff811c48d0>] ? blkdev_aio_write+0x0/0xa0
[<ffffffff811d4f64>] aio_rw_vect_retry+0x84/0x200
[<ffffffff811d6924>] aio_run_iocb+0x64/0x170
[<ffffffff811d7d51>] do_io_submit+0x291/0x920
[<ffffffff811d83f0>] sys_io_submit+0x10/0x20
[<ffffffff8100b072>] system_call_fastpath+0x16/0x1b
INFO: task fio:2723 blocked for more than 120 seconds.
Not tainted 2.6.32-431.el6.x86_64 #1
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
fio           D 0000000000000006     0  2723   2654 0x00000080
ffff88043bf5f698 0000000000000082 ffff88043bf5f628 ffffffff81058d53
ffff88043bf5f648 ffff880230e49cc0 ffff8802389aa228 ffff88043b2ad1b8
ffff88043a183ab8 ffff88043bf5ffd8 000000000000fbc8 ffff88043a183ab8
Call Trace:
[<ffffffff81058d53>] ? __wake_up+0x53/0x70
[<ffffffffa030334b>] ? md_raid5_unplug_device+0x7b/0x100 [raid456]
[<ffffffffa0304146>] get_active_stripe+0x236/0x830 [raid456]
[<ffffffff81065df0>] ? default_wake_function+0x0/0x20
[<ffffffff8109b5ce>] ? prepare_to_wait+0x4e/0x80
[<ffffffffa0308e15>] make_request+0x1b5/0xc6c [raid456]
[<ffffffff8109b2a0>] ? autoremove_wake_function+0x0/0x40
[<ffffffff811220e5>] ? mempool_alloc_slab+0x15/0x20
[<ffffffff81415b41>] md_make_request+0xe1/0x230
[<ffffffff811c3fd2>] ? bvec_alloc_bs+0x62/0x110
[<ffffffff811c32f0>] ? __bio_add_page+0x110/0x230
[<ffffffff81266c50>] generic_make_request+0x240/0x5a0
[<ffffffff811c742c>] ? do_direct_IO+0x57c/0xfa0
[<ffffffff81267020>] submit_bio+0x70/0x120
[<ffffffff811c8acd>] __blockdev_direct_IO_newtrunc+0xc7d/0x1270
[<ffffffff811c4330>] ? blkdev_get_block+0x0/0x20
[<ffffffff811c9137>] __blockdev_direct_IO+0x77/0xe0
[<ffffffff811c4330>] ? blkdev_get_block+0x0/0x20
[<ffffffff811c53b7>] blkdev_direct_IO+0x57/0x60
[<ffffffff811c4330>] ? blkdev_get_block+0x0/0x20
[<ffffffff81120552>] generic_file_direct_write+0xc2/0x190
[<ffffffff81121e71>] __generic_file_aio_write+0x3a1/0x490
[<ffffffff811d64c0>] ? aio_read_evt+0xa0/0x170
[<ffffffff811c490c>] blkdev_aio_write+0x3c/0xa0
[<ffffffff811c48d0>] ? blkdev_aio_write+0x0/0xa0
[<ffffffff811d4f64>] aio_rw_vect_retry+0x84/0x200
[<ffffffff811d6924>] aio_run_iocb+0x64/0x170
[<ffffffff811d7d51>] do_io_submit+0x291/0x920
[<ffffffff811d83f0>] sys_io_submit+0x10/0x20
[<ffffffff8100b072>] system_call_fastpath+0x16/0x1b
INFO: task fio:2724 blocked for more than 120 seconds.
Not tainted 2.6.32-431.el6.x86_64 #1
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
fio           D 000000000000000b     0  2724   2654 0x00000080
ffff88043be05698 0000000000000082 ffff88043be05628 ffffffff81058d53
ffff88043be05648 ffff880230e49cc0 ffff8802389aa228 ffff88043b2ad1b8
ffff88043a183058 ffff88043be05fd8 000000000000fbc8 ffff88043a183058
Call Trace:
[<ffffffff81058d53>] ? __wake_up+0x53/0x70
[<ffffffffa030334b>] ? md_raid5_unplug_device+0x7b/0x100 [raid456]
[<ffffffffa0304146>] get_active_stripe+0x236/0x830 [raid456]
[<ffffffff81065df0>] ? default_wake_function+0x0/0x20
[<ffffffff8109b5ce>] ? prepare_to_wait+0x4e/0x80
[<ffffffffa0308e15>] make_request+0x1b5/0xc6c [raid456]
[<ffffffff8109b2a0>] ? autoremove_wake_function+0x0/0x40
[<ffffffff811220e5>] ? mempool_alloc_slab+0x15/0x20
[<ffffffff81415b41>] md_make_request+0xe1/0x230
[<ffffffff811c3fd2>] ? bvec_alloc_bs+0x62/0x110
[<ffffffff811c32f0>] ? __bio_add_page+0x110/0x230
[<ffffffff81266c50>] generic_make_request+0x240/0x5a0
[<ffffffff811c742c>] ? do_direct_IO+0x57c/0xfa0
[<ffffffff81267020>] submit_bio+0x70/0x120
[<ffffffff811c8acd>] __blockdev_direct_IO_newtrunc+0xc7d/0x1270
[<ffffffff811c4330>] ? blkdev_get_block+0x0/0x20
[<ffffffff811c9137>] __blockdev_direct_IO+0x77/0xe0
[<ffffffff811c4330>] ? blkdev_get_block+0x0/0x20
[<ffffffff811c53b7>] blkdev_direct_IO+0x57/0x60
[<ffffffff811c4330>] ? blkdev_get_block+0x0/0x20
[<ffffffff81120552>] generic_file_direct_write+0xc2/0x190
[<ffffffff81121e71>] __generic_file_aio_write+0x3a1/0x490
[<ffffffff811d64c0>] ? aio_read_evt+0xa0/0x170
[<ffffffff811c490c>] blkdev_aio_write+0x3c/0xa0
[<ffffffff811c48d0>] ? blkdev_aio_write+0x0/0xa0
[<ffffffff811d4f64>] aio_rw_vect_retry+0x84/0x200
[<ffffffff811d6924>] aio_run_iocb+0x64/0x170
[<ffffffff811d7d51>] do_io_submit+0x291/0x920
[<ffffffff811d83f0>] sys_io_submit+0x10/0x20
[<ffffffff8100b072>] system_call_fastpath+0x16/0x1b
INFO: task fio:2725 blocked for more than 120 seconds.
Not tainted 2.6.32-431.el6.x86_64 #1
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
fio           D 0000000000000003     0  2725   2654 0x00000080
ffff88043be07698 0000000000000082 ffff88043be07628 ffffffff81058d53
ffff88043be07648 ffff880230e49cc0 ffff8802389aa228 ffff88043b2ad1b8
ffff88043a1825f8 ffff88043be07fd8 000000000000fbc8 ffff88043a1825f8
Call Trace:
[<ffffffff81058d53>] ? __wake_up+0x53/0x70
[<ffffffffa030334b>] ? md_raid5_unplug_device+0x7b/0x100 [raid456]
[<ffffffffa0304146>] get_active_stripe+0x236/0x830 [raid456]
[<ffffffff81065df0>] ? default_wake_function+0x0/0x20
[<ffffffff8109b5ce>] ? prepare_to_wait+0x4e/0x80
[<ffffffffa0308e15>] make_request+0x1b5/0xc6c [raid456]
[<ffffffff8109b2a0>] ? autoremove_wake_function+0x0/0x40
[<ffffffff811220e5>] ? mempool_alloc_slab+0x15/0x20
[<ffffffff81415b41>] md_make_request+0xe1/0x230
[<ffffffff811c3fd2>] ? bvec_alloc_bs+0x62/0x110
[<ffffffff811c32f0>] ? __bio_add_page+0x110/0x230
[<ffffffff81266c50>] generic_make_request+0x240/0x5a0
[<ffffffff811c742c>] ? do_direct_IO+0x57c/0xfa0
[<ffffffff81267020>] submit_bio+0x70/0x120
[<ffffffff811c8acd>] __blockdev_direct_IO_newtrunc+0xc7d/0x1270
[<ffffffff811c4330>] ? blkdev_get_block+0x0/0x20
[<ffffffff811c9137>] __blockdev_direct_IO+0x77/0xe0
[<ffffffff811c4330>] ? blkdev_get_block+0x0/0x20
[<ffffffff811c53b7>] blkdev_direct_IO+0x57/0x60
[<ffffffff811c4330>] ? blkdev_get_block+0x0/0x20
[<ffffffff81120552>] generic_file_direct_write+0xc2/0x190
[<ffffffff81121e71>] __generic_file_aio_write+0x3a1/0x490
[<ffffffff811d64c0>] ? aio_read_evt+0xa0/0x170
[<ffffffff811c490c>] blkdev_aio_write+0x3c/0xa0
[<ffffffff811c48d0>] ? blkdev_aio_write+0x0/0xa0
[<ffffffff811d4f64>] aio_rw_vect_retry+0x84/0x200
[<ffffffff811d6924>] aio_run_iocb+0x64/0x170
[<ffffffff811d7d51>] do_io_submit+0x291/0x920
[<ffffffff811d83f0>] sys_io_submit+0x10/0x20
[<ffffffff8100b072>] system_call_fastpath+0x16/0x1b

[root@root ~]# cat /proc/2690/stack
[<ffffffff810686da>] __cond_resched+0x2a/0x40
[<ffffffffa030361c>] ops_run_io+0x2c/0x920 [raid456]
[<ffffffffa03052cc>] handle_stripe+0x9cc/0x2980 [raid456]
[<ffffffffa03078a4>] raid5d+0x624/0x850 [raid456]
[<ffffffff81416f05>] md_thread+0x115/0x150
[<ffffffff8109aef6>] kthread+0x96/0xa0
[<ffffffff8100c20a>] child_rip+0xa/0x20
[<ffffffffffffffff>] 0xffffffffffffffff

[root@root ~]# cat /proc/2690/stat
2690 (md0_raid5) R 2 0 0 0 -1 2149613632 0 0 0 0 0 68495 0 0 20 0 1 0 350990 0 0 18446744073709551615 0 0 0 0 0 0 0 2147483391 256 0 0 0 17 2 0 0 6855 0 0
[root@root ~]# cat /proc/2690/statm
0 0 0 0 0 0 0
[root@root ~]# cat /proc/2690/stat
stat    statm   status
[root@root ~]# cat /proc/2690/status
Name:   md0_raid5
State:  R (running)
Tgid:   2690
Pid:    2690
PPid:   2
TracerPid:      0
Uid:    0       0       0       0
Gid:    0       0       0       0
Utrace: 0
FDSize: 64
Groups:
Threads:        1
SigQ:   2/128402
SigPnd: 0000000000000000
ShdPnd: 0000000000000000
SigBlk: 0000000000000000
SigIgn: fffffffffffffeff
SigCgt: 0000000000000100
CapInh: 0000000000000000
CapPrm: ffffffffffffffff
CapEff: fffffffffffffeff
CapBnd: ffffffffffffffff
Cpus_allowed:   ffffff
Cpus_allowed_list:      0-23
Mems_allowed:   00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000003
Mems_allowed_list:      0-1
voluntary_ctxt_switches:        5411612
nonvoluntary_ctxt_switches:     257032


Thanks,
Manibalan.