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126d9d4952
How the rdp->cblist enabled state is treated at CPU-hotplug time depends on whether or not that ->cblist is offloaded. 1) Not offloaded: The ->cblist is disabled when the CPU goes down. All its callbacks are migrated and none can to enqueued until after some later CPU-hotplug operation brings the CPU back up. 2) Offloaded: The ->cblist is not disabled on CPU down because the CB/GP kthreads must finish invoking the remaining callbacks. There is thus no need to re-enable it on CPU up. Since the ->cblist offloaded state is set in stone at boot, it cannot change between CPU down and CPU up. So 1) and 2) are symmetrical. However, given runtime toggling of the offloaded state, there are two additional asymmetrical scenarios: 3) The ->cblist is not offloaded when the CPU goes down. The ->cblist is later toggled to offloaded and then the CPU comes back up. 4) The ->cblist is offloaded when the CPU goes down. The ->cblist is later toggled to no longer be offloaded and then the CPU comes back up. Scenario 4) is currently handled correctly. The ->cblist remains enabled on CPU down and gets re-initialized on CPU up. The toggling operation will wait until ->cblist is empty, so ->cblist will remain empty until CPU-up time. The scenario 3) would run into trouble though, as the rdp is disabled on CPU down and not re-initialized/re-enabled on CPU up. Except that in this case, ->cblist is guaranteed to be empty because all its callbacks were migrated away at CPU-down time. And the CPU-up code already initializes and enables any empty ->cblist structures in order to handle the possibility of early-boot invocations of call_rcu() in the case where such invocations don't occur. So all that need be done is to adjust the locking. Cc: Josh Triplett <josh@joshtriplett.org> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Cc: Lai Jiangshan <jiangshanlai@gmail.com> Cc: Joel Fernandes <joel@joelfernandes.org> Cc: Neeraj Upadhyay <neeraju@codeaurora.org> Cc: Thomas Gleixner <tglx@linutronix.de> Inspired-by: Paul E. McKenney <paulmck@kernel.org> Tested-by: Boqun Feng <boqun.feng@gmail.com> Signed-off-by: Frederic Weisbecker <frederic@kernel.org> Signed-off-by: Paul E. McKenney <paulmck@kernel.org> |
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| .. | ||
| Kconfig | ||
| Kconfig.debug | ||
| Makefile | ||
| rcu.h | ||
| rcu_segcblist.c | ||
| rcu_segcblist.h | ||
| rcuscale.c | ||
| rcutorture.c | ||
| refscale.c | ||
| srcutiny.c | ||
| srcutree.c | ||
| sync.c | ||
| tasks.h | ||
| tiny.c | ||
| tree.c | ||
| tree.h | ||
| tree_exp.h | ||
| tree_plugin.h | ||
| tree_stall.h | ||
| update.c | ||