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rcu-tasks: Handle idle tasks for recently offlined CPUs

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This commit identifies idle tasks for recently offlined CPUs as residing
in a quiescent state.  This is safe only because CPU-hotplug operations
are excluded during these checks.

Signed-off-by: Paul E. McKenney <paulmck@kernel.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>
This commit is contained in:
Paul E. McKenney 2022-05-24 18:02:40 -07:00
parent 5c9a9ca44f
commit 897ba84dc5
1 changed files with 7 additions and 8 deletions
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15
kernel/rcu/tasks.h
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@ -1318,27 +1318,26 @@ static int trc_inspect_reader(struct task_struct *t, void *bhp_in)
int nesting;
bool ofl = cpu_is_offline(cpu);
if (task_curr(t)) {
WARN_ON_ONCE(ofl && !is_idle_task(t));
if (task_curr(t) && !ofl) {
// If no chance of heavyweight readers, do it the hard way.
if (!ofl && !IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB))
if (!IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB))
return -EINVAL;
// If heavyweight readers are enabled on the remote task,
// we can inspect its state despite its currently running.
// However, we cannot safely change its state.
n_heavy_reader_attempts++;
if (!ofl && // Check for "running" idle tasks on offline CPUs.
!rcu_dynticks_zero_in_eqs(cpu, &t->trc_reader_nesting))
// Check for "running" idle tasks on offline CPUs.
if (!rcu_dynticks_zero_in_eqs(cpu, &t->trc_reader_nesting))
return -EINVAL; // No quiescent state, do it the hard way.
n_heavy_reader_updates++;
if (ofl)
n_heavy_reader_ofl_updates++;
nesting = 0;
} else {
// The task is not running, so C-language access is safe.
nesting = t->trc_reader_nesting;
WARN_ON_ONCE(ofl && task_curr(t) && !is_idle_task(t));
if (IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB) && ofl)
n_heavy_reader_ofl_updates++;
}
// If not exiting a read-side critical section, mark as checked