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powerpc: protect cpu offlining by RCU offline lock #2

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Pull request for series with
subject: powerpc: protect cpu offlining by RCU offline lock
version: 1
url: https://patchwork.kernel.org/project/rcu/list/?series=676744

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Master branch: 2f91146
series: https://patchwork.kernel.org/project/rcu/list/?series=676744
version: 1

kernel-patches-bot pushed a commit that referenced this pull request Sep 23, 2022
@joelagnel @chantra
rcu/nocb: Fix possible bugs in rcu_barrier()
c447410 
When going through the lazy-rcu work, I noticed that
rcu_barrier_entrain() does not really wake up the rcuog GP thread in any
path after entraining. This means it is possible the GP thread is not
awakened soon (say there were no CBs in the cblist after entraining
time).

Further, nothing appears to be calling the rcu_barrier callback
directly in the case the ->cblist was empty which means if the IPI gets
delayed enough to make the ->cblist empty and it turns out to be the last
CPU holding, then nothing calls completes rcu_state.barrier_completion.

Fix both these issues.

A note on the wakeup, there are 3 cases AFAICS after the call to
rcu_nocb_flush_bypass():

1. The rdp->cblist has pending CBs.

2. The rdp->cblist has all done CBs.

3. The rdp->cblist has no CBs at all (say the IPI took a long time to
arrive and some other path dequeued them in the meanwhile).

For #3, entraining a CB is not needed and we should bail.  For #1 and
needed. But for #2 it is needed.

Signed-off-by: Joel Fernandes (Google) <[email protected]>
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Master branch: 80fc02e
series: https://patchwork.kernel.org/project/rcu/list/?series=676744
version: 1

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Master branch: 80fc02e
series: https://patchwork.kernel.org/project/rcu/list/?series=676744
version: 1

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Master branch: 80fc02e
series: https://patchwork.kernel.org/project/rcu/list/?series=676744
version: 1

Pull request is NOT updated. Failed to apply https://patchwork.kernel.org/project/rcu/list/?series=676744
error message:

Cmd('git') failed due to: exit code(128)
  cmdline: git am -3
  stderr: 'fatal: Dirty index: cannot apply patches (dirty: .github/workflows/test.yml)'

conflict:

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Master branch: 32fad12
series: https://patchwork.kernel.org/project/rcu/list/?series=676744
version: 1

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Master branch: 32fad12
series: https://patchwork.kernel.org/project/rcu/list/?series=676744
version: 1

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Master branch: 32fad12
series: https://patchwork.kernel.org/project/rcu/list/?series=676744
version: 1

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Master branch: 32fad12
series: https://patchwork.kernel.org/project/rcu/list/?series=676744
version: 1

@kernel-patches-bot kernel-patches-bot force-pushed the series/676744=>rcu-dev branch 12 times, most recently from b2ce6cd to 53bd5c6 Compare October 20, 2022 16:37
@zhouzhouyi-hub @chantra
powerpc: protect cpu offlining by RCU offline lock
8697218 
During the cpu offlining, the sub functions of xive_teardown_cpu will
call __lock_acquire when CONFIG_LOCKDEP=y. The latter function will
travel RCU protected list, so "WARNING: suspicious RCU usage" will be
triggered.

Try to protect cpu offlining by RCU offline lock.

Tested on PPC VM of Open Source Lab of Oregon State University.
(Each round of tests takes about 19 hours to finish)
Test results show that although "WARNING: suspicious RCU usage" has gone,
but there are more "BUG: soft lockup" reports than the original kernel
(10 vs 6), so I add a [RFC] to my subject line.

Signed-off-by: Zhouyi Zhou <[email protected]>
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