Re: [PATCH] rcu: Make nocb leader kthreads process pending callbacks after spawning

Amit Shah
2014-08-28T05:47:13Z

On (Wed) 27 Aug 2014 [16:43:40], Pranith Kumar wrote:
> The nocb callbacks generated before the nocb kthreads are spawned are
> enqueued in the nocb queue for later processing. Commit fbce7497ee5af ("rcu:
> Parallelize and economize NOCB kthread wakeups") introduced nocb leader kthreads
> which checked the nocb_leader_wake flag to see if there were any such pending
> callbacks. A case was reported in which newly spawned leader kthreads were not
> processing the pending callbacks as this flag was not set, which led to a boot
> hang.
>
> The following commit ensures that the newly spawned nocb kthreads process the
> pending callbacks by allowing the kthreads to run immediately after spawning
> instead of waiting. This is done by inverting the logic of nocb_leader_wake
> tests to nocb_leader_sleep which allows us to use the default initialization of
> this flag to 0 to let the kthreads run.
>
> Reported-by: Amit Shah <amit.shah@redhat.com>
> Signed-off-by: Pranith Kumar <bobby.prani@gmail.com>
> Link: http://www.spinics.net/lists/kernel/msg1802899.html
> ---
> kernel/rcu/tree.h | 2 +-
> kernel/rcu/tree_plugin.h | 24 ++++++++++++------------
> 2 files changed, 13 insertions(+), 13 deletions(-)

I'd have split this into two patches: one for the variable rename and
one for fixing the bug.

However, the backport Paul posted does work fine for me on master, so
you can add my

Tested-by: Amit Shah <amit.shah@redhat.com>

Thanks,

Amit