Messages in this thread | | | Date | Mon, 22 Oct 2012 11:33:16 +0800 | From | Tang Chen <> | Subject | Re: [PATCH v2 2/2] Do not change worker's running cpu in cmci_rediscover(). |
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On 10/20/2012 01:21 AM, Luck, Tony wrote: >> In this case, the following BUG_ON in try_to_wake_up_local() will be triggered: >> BUG_ON(rq != this_rq()); > > Logically this looks OK - what is the test case to trigger this? I've done a moderate > amount of testing of cpu online/offline while injecting corrected errors (when testing > the CMCI storm patches) ... but didn't see this problem.
Hi Tony, Borislav,
Here is my case.
I have 2 nodes, node0 and node1. node1 could be hotpluged. node0 has cpu0 ~ cpu15, node1 has cpu16 ~ cpu31.
I online all the cpus on node1, and hot-remove node1 directly.
When this problem is triggered, current is a work thread.
For example: cpu20 is dying. current is on cpu21, it migrates itself to cpu22.
Assume current is process1, and it is a work thread.
cpu21 cpu22 p1: .... cmci_rediscover() |-set_cpus_allowed_ptr() |-stop_one_cpu() |-create a work to excute migration_cpu_stop() |-wait_for_completion() |-wait_for_common() |-might_sleep() Here, p1 gives up cpu21.
The work starts: migration_cpu_stop() |-migrate p1 to cpu22
On cpu22, p1 wakes up: p1: In wait_for_common() |-do_wait_for_common() |-schedule_timeout() |-schedule() |-__schedule() |-try_to_wake_up_local() |-wq_worker_sleeping() |-BUG_ON(rq != this_rq())
On cpu22, wq_worker_sleeping() uses p1's worker_pool to find a worker to go on to execute p1. But p1's worker_pool is on cpu21, and p1 is now on cpu22. So the BUG_ON(rq != this_rq()) is triggered.
Thanks. :)
> > -Tony >
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