Repeated kernel hangs on 2.6.32-220.2.1.el6: umount stuck in synchronize_sched_expedited for 9 hours
Issue
- NFS umount stuck in synchronize_sched_expedited() for 9 hours.
- Using sysrq to trigger a core dump and examining the core shows the the NFS umount process stuck with a backtrace similar to the following
PID: 31208 TASK: ffff88063b78cac0 CPU: 0 COMMAND: "umount"
#0 [ffff8805f4313b48] schedule at ffffffff814eca93
#1 [ffff8805f4313c10] schedule_timeout at ffffffff814ed985
#2 [ffff8805f4313cc0] wait_for_common at ffffffff814ed603
#3 [ffff8805f4313d50] wait_for_completion at ffffffff814ed71d
#4 [ffff8805f4313d60] synchronize_sched_expedited at ffffffff81062f51
#5 [ffff8805f4313dc0] synchronize_rcu_expedited at ffffffff810ddc7e
#6 [ffff8805f4313dd0] bdi_remove_from_list at ffffffff811340ea
#7 [ffff8805f4313df0] bdi_unregister at ffffffff811341b1
#8 [ffff8805f4313e20] nfs_put_super at ffffffffa04899e9 [nfs]
#9 [ffff8805f4313e30] generic_shutdown_super at ffffffff8117864b
#10 [ffff8805f4313e50] kill_anon_super at ffffffff81178736
#11 [ffff8805f4313e70] nfs_kill_super at ffffffffa048c415 [nfs]
#12 [ffff8805f4313e90] deactivate_super at ffffffff811796c0
#13 [ffff8805f4313eb0] mntput_no_expire at ffffffff8119563f
#14 [ffff8805f4313ee0] sys_umount at ffffffff811960db
Environment
- Red Hat Enterprise Linux 6
- kernels prior to 2.6.32-358.el6
- seen on 2.6.32-220.2.1.el6
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