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Currently, the RCU Tasks Trace grace-period kthread IPIs each online CPU using smp_call_function_single() in order to track any tasks currently in RCU Tasks Trace read-side critical sections during which the corresponding task has neither blocked nor been preempted. These IPIs are annoying and are also not strictly necessary because any task that blocks or is preempted within its current RCU Tasks Trace read-side critical section will be tracked on one of the per-CPU rcu_tasks_percpu structure's ->rtp_blkd_tasks list. So the only time that this is a problem is if one of the CPUs runs through a long-duration RCU Tasks Trace read-side critical section without a context switch. Note that the task_call_func() function cannot help here because there is no safe way to identify the target task. Of course, the task_call_func() function will be very useful later, when processing the list of tasks, but it needs to know the task. This commit therefore creates a cpu_curr_snapshot() function that returns a pointer the task_struct structure of some task that happened to be running on the specified CPU more or less during the time that the cpu_curr_snapshot() function was executing. If there was no context switch during this time, this function will return a pointer to the task_struct structure of the task that was running throughout. If there was a context switch, then the outgoing task will be taken care of by RCU's context-switch hook, and the incoming task was either already taken care during some previous context switch, or it is not currently within an RCU Tasks Trace read-side critical section. And in this latter case, the grace period already started, so there is no need to wait on this task. This new cpu_curr_snapshot() function is invoked on each CPU early in the RCU Tasks Trace grace-period processing, and the resulting tasks are queued for later quiescent-state inspection. Signed-off-by: Paul E. McKenney <paulmck@kernel.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Neeraj Upadhyay <quic_neeraju@quicinc.com> Cc: Eric Dumazet <edumazet@google.com> Cc: Alexei Starovoitov <ast@kernel.org> Cc: Andrii Nakryiko <andrii@kernel.org> Cc: Martin KaFai Lau <kafai@fb.com> Cc: KP Singh <kpsingh@kernel.org> |
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| .. | ||
| Kconfig | ||
| Kconfig.debug | ||
| Makefile | ||
| rcu_segcblist.c | ||
| rcu_segcblist.h | ||
| rcu.h | ||
| rcuscale.c | ||
| rcutorture.c | ||
| refscale.c | ||
| srcutiny.c | ||
| srcutree.c | ||
| sync.c | ||
| tasks.h | ||
| tiny.c | ||
| tree_exp.h | ||
| tree_nocb.h | ||
| tree_plugin.h | ||
| tree_stall.h | ||
| tree.c | ||
| tree.h | ||
| update.c | ||