On Mon, Aug 26, 2013 at 09:45:15AM -0400, Tomoki Sekiyama wrote: > The soft lockup below happes at the boot time of the system using dm > multipath and automated elevator switching udev rules. > > [ 356.127001] BUG: soft lockup - CPU#3 stuck for 22s! [sh:483] > [ 356.127001] RIP: 0010:[<ffffffff81072a7d>] [<ffffffff81072a7d>] > lock_timer_base.isra.35+0x1d/0x50 > ... > [ 356.127001] Call Trace: > [ 356.127001] [<ffffffff81073810>] try_to_del_timer_sync+0x20/0x70 > [ 356.127001] [<ffffffff8118b08a>] ? kmem_cache_alloc_node_trace+0x20a/0x230 > [ 356.127001] [<ffffffff810738b2>] del_timer_sync+0x52/0x60 > [ 356.127001] [<ffffffff812ece22>] cfq_exit_queue+0x32/0xf0 > [ 356.127001] [<ffffffff812c98df>] elevator_exit+0x2f/0x50 > [ 356.127001] [<ffffffff812c9f21>] elevator_change+0xf1/0x1c0 > [ 356.127001] [<ffffffff812caa50>] elv_iosched_store+0x20/0x50 > [ 356.127001] [<ffffffff812d1d09>] queue_attr_store+0x59/0xb0 > [ 356.127001] [<ffffffff812143f6>] sysfs_write_file+0xc6/0x140 > [ 356.127001] [<ffffffff811a326d>] vfs_write+0xbd/0x1e0 > [ 356.127001] [<ffffffff811a3ca9>] SyS_write+0x49/0xa0 > [ 356.127001] [<ffffffff8164e899>] system_call_fastpath+0x16/0x1b > > This is caused by a race between md device initialization and sysfs knob > to switch the scheduler.
I think we can also improve changelog a bit. So IIUC, softlockup happens because one thread called del_timer_sync() on a timer which was not even initilized. Timer initialization should have happened in cfq_init_queue() using init_timer(). But before init_timer() could be called, elevator switch path called del_timer_sync(). del_timer_sync() in turn calls lock_timer_base() which will loop infinitely if timer->base == NULL. And because we have not called init_timer() yet, I am assuming timer->base is null? Is this right analysis? If yes, then this patch should most likely fix following bz. https://bugzilla.redhat.com/show_bug.cgi?id=902012 I had concluded that some how timer->base is NULL but could not understand how come timer base is NULL when we have called init_timer() on it. Thanks Vivek -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
