yumBackend.py became unresponsive and system crashed with "Kernel panic - not syncing: hung_task: blocked tasks" error.

Issue

• RHEL 6.0 Server rebooted suddenly and generated the vmcore file.

INFO: task yumBackend.py:348 blocked for more than 120 seconds.
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
yumBackend.py D 0000000000000000     0   348  12621 0x00000008
 ffff88004e03b638 0000000000000082 ffff88004e03b600 ffff88004e03b5fc
 0000000000000000 ffff880197828400 ffff88002dc35f80 000000012b7cfd97
 ffff880101439ab8 ffff88004e03bfd8 000000000000f598 ffff880101439ab8
Call Trace:
 [<ffffffff811a3ce0>] ? sync_buffer+0x0/0x50
 [<ffffffff814db6c3>] io_schedule+0x73/0xc0
 [<ffffffff811a3d20>] sync_buffer+0x40/0x50
 [<ffffffff814dbf2f>] __wait_on_bit+0x5f/0x90
 [<ffffffff811a3ce0>] ? sync_buffer+0x0/0x50
 [<ffffffff814dbfd8>] out_of_line_wait_on_bit+0x78/0x90
 [<ffffffff8108e160>] ? wake_bit_function+0x0/0x50
 [<ffffffff811a3cd6>] __wait_on_buffer+0x26/0x30
 [<ffffffff811a4d0d>] bh_submit_read+0x4d/0x80
 [<ffffffffa0252868>] ext4_ext_find_extent+0x248/0x320 [ext4]
 [<ffffffffa02549ac>] ext4_ext_get_blocks+0x12c/0x19a0 [ext4]
 [<ffffffff811a39e6>] ? __set_page_dirty_buffers+0x46/0xc0
 [<ffffffff8106dcb7>] ? current_fs_time+0x27/0x30
 [<ffffffff811a5fef>] ? __block_page_mkwrite+0xdf/0x120
 [<ffffffff811373c5>] ? __do_fault+0x275/0x510
 [<ffffffff81165f18>] ? __mem_cgroup_try_charge+0x78/0x420
 [<ffffffffa0233b1a>] ext4_get_blocks+0x7a/0x2a0 [ext4]
 [<ffffffff81137757>] ? handle_pte_fault+0xf7/0xb50
 [<ffffffffa023460d>] ext4_get_block+0xbd/0x120 [ext4]
 [<ffffffff811aca80>] do_mpage_readpage+0x150/0x5f0
 [<ffffffff8110d789>] ? add_to_page_cache_locked+0xc9/0x140
 [<ffffffff811ad079>] mpage_readpages+0xe9/0x130
 [<ffffffffa0234550>] ? ext4_get_block+0x0/0x120 [ext4]
 [<ffffffffa0233d40>] ? ext4_da_get_block_prep+0x0/0x3c0 [ext4]
 [<ffffffffa0234550>] ? ext4_get_block+0x0/0x120 [ext4]
 [<ffffffff811546da>] ? alloc_pages_current+0xaa/0x110
 [<ffffffffa022f8fd>] ext4_readpages+0x1d/0x20 [ext4]
 [<ffffffff81122bf5>] __do_page_cache_readahead+0x185/0x210
 [<ffffffff81122ca1>] ra_submit+0x21/0x30
 [<ffffffff81123015>] ondemand_readahead+0x115/0x240
 [<ffffffff81123233>] page_cache_sync_readahead+0x33/0x50
 [<ffffffff8110efd8>] generic_file_aio_read+0x558/0x700
 [<ffffffff8117263a>] do_sync_read+0xfa/0x140
 [<ffffffff8108e120>] ? autoremove_wake_function+0x0/0x40
 [<ffffffff81177b34>] ? cp_new_stat+0xe4/0x100
 [<ffffffff81205356>] ? security_file_permission+0x16/0x20
 [<ffffffff81173065>] vfs_read+0xb5/0x1a0
 [<ffffffff81173392>] sys_pread64+0x82/0xa0
 [<ffffffff8100b172>] system_call_fastpath+0x16/0x1b
Kernel panic - not syncing: hung_task: blocked tasks