rcu: Make exit_rcu() more precise and consolidate
When running preemptible RCU, if a task exits in an RCU read-side critical section having blocked within that same RCU read-side critical section, the task must be removed from the list of tasks blocking a grace period (perhaps the current grace period, perhaps the next grace period, depending on timing). The exit() path invokes exit_rcu() to do this cleanup. However, the current implementation of exit_rcu() needlessly does the cleanup even if the task did not block within the current RCU read-side critical section, which wastes time and needlessly increases the size of the state space. Fix this by only doing the cleanup if the current task is actually on the list of tasks blocking some grace period. While we are at it, consolidate the two identical exit_rcu() functions into a single function. Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Tested-by: Linus Torvalds <torvalds@linux-foundation.org> Conflicts: kernel/rcupdate.c
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