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author | Paul E. McKenney <paulmck@kernel.org> | 2022-05-18 16:06:55 -0700 |
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committer | Paul E. McKenney <paulmck@kernel.org> | 2022-06-20 09:22:29 -0700 |
commit | 7460ade1fc6e3f62d5c0006c972755f0aefd41b2 (patch) | |
tree | e4f7da681c9e996dacf70d252ecaf73c9e9b440a /kernel | |
parent | 19415004d5221ba59be6ef566fdbb52c44808f7e (diff) | |
download | linux-7460ade1fc6e3f62d5c0006c972755f0aefd41b2.tar.gz linux-7460ade1fc6e3f62d5c0006c972755f0aefd41b2.tar.bz2 linux-7460ade1fc6e3f62d5c0006c972755f0aefd41b2.zip |
rcu-tasks: Scan running tasks for RCU Tasks Trace readers
A running task might be within an RCU Tasks Trace read-side critical
section for any length of time, but will not be placed on any of the
per-CPU rcu_tasks_percpu structure's ->rtp_blkd_tasks lists. Therefore
any RCU Tasks Trace grace-period processing that does not scan the full
task list must interact with the running tasks.
This commit therefore causes the rcu_tasks_trace_pregp_step() function
to IPI each CPU in order to place the corresponding task on the holdouts
list and to record whether or not it was in an RCU Tasks Trace read-side
critical section. Yes, it is possible to avoid adding it to that list
if it is not a reader, but that would prevent the system from remembering
that this task was in a quiescent state. Which is why the running tasks
are unconditionally added to the holdout list.
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>
Diffstat (limited to 'kernel')
-rw-r--r-- | kernel/rcu/tasks.h | 51 |
1 files changed, 40 insertions, 11 deletions
diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h index 1aa6a24a9bc2..a8f95864c921 100644 --- a/kernel/rcu/tasks.h +++ b/kernel/rcu/tasks.h @@ -14,7 +14,7 @@ struct rcu_tasks; typedef void (*rcu_tasks_gp_func_t)(struct rcu_tasks *rtp); -typedef void (*pregp_func_t)(void); +typedef void (*pregp_func_t)(struct list_head *hop); typedef void (*pertask_func_t)(struct task_struct *t, struct list_head *hop); typedef void (*postscan_func_t)(struct list_head *hop); typedef void (*holdouts_func_t)(struct list_head *hop, bool ndrpt, bool *frptp); @@ -661,7 +661,7 @@ static void rcu_tasks_wait_gp(struct rcu_tasks *rtp) struct task_struct *t; set_tasks_gp_state(rtp, RTGS_PRE_WAIT_GP); - rtp->pregp_func(); + rtp->pregp_func(&holdouts); /* * There were callbacks, so we need to wait for an RCU-tasks @@ -791,7 +791,7 @@ static void rcu_tasks_wait_gp(struct rcu_tasks *rtp) // disabling. /* Pre-grace-period preparation. */ -static void rcu_tasks_pregp_step(void) +static void rcu_tasks_pregp_step(struct list_head *hop) { /* * Wait for all pre-existing t->on_rq and t->nvcsw transitions @@ -1449,24 +1449,48 @@ static void trc_wait_for_one_reader(struct task_struct *t, } } -/* Do first-round processing for the specified task. */ -static void rcu_tasks_trace_pertask(struct task_struct *t, - struct list_head *hop) +/* + * Initialize for first-round processing for the specified task. + * Return false if task is NULL or already taken care of, true otherwise. + */ +static bool rcu_tasks_trace_pertask_prep(struct task_struct *t, bool notself) { // During early boot when there is only the one boot CPU, there // is no idle task for the other CPUs. Also, the grace-period // kthread is always in a quiescent state. In addition, just return // if this task is already on the list. - if (unlikely(t == NULL) || t == current || !list_empty(&t->trc_holdout_list)) - return; + if (unlikely(t == NULL) || (t == current && notself) || !list_empty(&t->trc_holdout_list)) + return false; rcu_st_need_qs(t, 0); t->trc_ipi_to_cpu = -1; - trc_wait_for_one_reader(t, hop); + return true; +} + +/* Do first-round processing for the specified task. */ +static void rcu_tasks_trace_pertask(struct task_struct *t, struct list_head *hop) +{ + if (rcu_tasks_trace_pertask_prep(t, true)) + trc_wait_for_one_reader(t, hop); +} + +/* + * Get the current CPU's current task on the holdout list. + * Calls to this function must be serialized. + */ +static void rcu_tasks_trace_pertask_handler(void *hop_in) +{ + struct list_head *hop = hop_in; + struct task_struct *t = current; + + // Pull in the currently running task, but only if it is currently + // in an RCU tasks trace read-side critical section. + if (rcu_tasks_trace_pertask_prep(t, false)) + trc_add_holdout(t, hop); } /* Initialize for a new RCU-tasks-trace grace period. */ -static void rcu_tasks_trace_pregp_step(void) +static void rcu_tasks_trace_pregp_step(struct list_head *hop) { int cpu; @@ -1474,9 +1498,14 @@ static void rcu_tasks_trace_pregp_step(void) for_each_possible_cpu(cpu) WARN_ON_ONCE(per_cpu(trc_ipi_to_cpu, cpu)); - // Disable CPU hotplug across the tasklist scan. + // Disable CPU hotplug across the CPU scan. // This also waits for all readers in CPU-hotplug code paths. cpus_read_lock(); + + // These smp_call_function_single() calls are serialized to + // allow safe access to the hop list. + for_each_online_cpu(cpu) + smp_call_function_single(cpu, rcu_tasks_trace_pertask_handler, hop, 1); } /* |