linux/kernel/rcu/update.c
Uladzislau Rezki 28b3ae4265 rcu: Introduce CONFIG_RCU_EXP_CPU_STALL_TIMEOUT
Currently both expedited and regular grace period stall warnings use
a single timeout value that with units of seconds.  However, recent
Android use cases problem require a sub-100-millisecond expedited RCU CPU
stall warning.  Given that expedited RCU grace periods normally complete
in far less than a single millisecond, especially for small systems,
this is not unreasonable.

Therefore introduce the CONFIG_RCU_EXP_CPU_STALL_TIMEOUT kernel
configuration that defaults to 20 msec on Android and remains the same
as that of the non-expedited stall warnings otherwise.  It also can be
changed in run-time via: /sys/.../parameters/rcu_exp_cpu_stall_timeout.

[ paulmck: Default of zero to use CONFIG_RCU_STALL_TIMEOUT. ]

Signed-off-by: Uladzislau Rezki <uladzislau.rezki@sony.com>
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2022-05-11 11:38:50 -07:00

616 lines
18 KiB
C

// SPDX-License-Identifier: GPL-2.0+
/*
* Read-Copy Update mechanism for mutual exclusion
*
* Copyright IBM Corporation, 2001
*
* Authors: Dipankar Sarma <dipankar@in.ibm.com>
* Manfred Spraul <manfred@colorfullife.com>
*
* Based on the original work by Paul McKenney <paulmck@linux.ibm.com>
* and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
* Papers:
* http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf
* http://lse.sourceforge.net/locking/rclock_OLS.2001.05.01c.sc.pdf (OLS2001)
*
* For detailed explanation of Read-Copy Update mechanism see -
* http://lse.sourceforge.net/locking/rcupdate.html
*
*/
#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/spinlock.h>
#include <linux/smp.h>
#include <linux/interrupt.h>
#include <linux/sched/signal.h>
#include <linux/sched/debug.h>
#include <linux/atomic.h>
#include <linux/bitops.h>
#include <linux/percpu.h>
#include <linux/notifier.h>
#include <linux/cpu.h>
#include <linux/mutex.h>
#include <linux/export.h>
#include <linux/hardirq.h>
#include <linux/delay.h>
#include <linux/moduleparam.h>
#include <linux/kthread.h>
#include <linux/tick.h>
#include <linux/rcupdate_wait.h>
#include <linux/sched/isolation.h>
#include <linux/kprobes.h>
#include <linux/slab.h>
#include <linux/irq_work.h>
#include <linux/rcupdate_trace.h>
#define CREATE_TRACE_POINTS
#include "rcu.h"
#ifdef MODULE_PARAM_PREFIX
#undef MODULE_PARAM_PREFIX
#endif
#define MODULE_PARAM_PREFIX "rcupdate."
#ifndef CONFIG_TINY_RCU
module_param(rcu_expedited, int, 0444);
module_param(rcu_normal, int, 0444);
static int rcu_normal_after_boot = IS_ENABLED(CONFIG_PREEMPT_RT);
#if !defined(CONFIG_PREEMPT_RT) || defined(CONFIG_NO_HZ_FULL)
module_param(rcu_normal_after_boot, int, 0444);
#endif
#endif /* #ifndef CONFIG_TINY_RCU */
#ifdef CONFIG_DEBUG_LOCK_ALLOC
/**
* rcu_read_lock_held_common() - might we be in RCU-sched read-side critical section?
* @ret: Best guess answer if lockdep cannot be relied on
*
* Returns true if lockdep must be ignored, in which case ``*ret`` contains
* the best guess described below. Otherwise returns false, in which
* case ``*ret`` tells the caller nothing and the caller should instead
* consult lockdep.
*
* If CONFIG_DEBUG_LOCK_ALLOC is selected, set ``*ret`` to nonzero iff in an
* RCU-sched read-side critical section. In absence of
* CONFIG_DEBUG_LOCK_ALLOC, this assumes we are in an RCU-sched read-side
* critical section unless it can prove otherwise. Note that disabling
* of preemption (including disabling irqs) counts as an RCU-sched
* read-side critical section. This is useful for debug checks in functions
* that required that they be called within an RCU-sched read-side
* critical section.
*
* Check debug_lockdep_rcu_enabled() to prevent false positives during boot
* and while lockdep is disabled.
*
* Note that if the CPU is in the idle loop from an RCU point of view (ie:
* that we are in the section between rcu_idle_enter() and rcu_idle_exit())
* then rcu_read_lock_held() sets ``*ret`` to false even if the CPU did an
* rcu_read_lock(). The reason for this is that RCU ignores CPUs that are
* in such a section, considering these as in extended quiescent state,
* so such a CPU is effectively never in an RCU read-side critical section
* regardless of what RCU primitives it invokes. This state of affairs is
* required --- we need to keep an RCU-free window in idle where the CPU may
* possibly enter into low power mode. This way we can notice an extended
* quiescent state to other CPUs that started a grace period. Otherwise
* we would delay any grace period as long as we run in the idle task.
*
* Similarly, we avoid claiming an RCU read lock held if the current
* CPU is offline.
*/
static bool rcu_read_lock_held_common(bool *ret)
{
if (!debug_lockdep_rcu_enabled()) {
*ret = true;
return true;
}
if (!rcu_is_watching()) {
*ret = false;
return true;
}
if (!rcu_lockdep_current_cpu_online()) {
*ret = false;
return true;
}
return false;
}
int rcu_read_lock_sched_held(void)
{
bool ret;
if (rcu_read_lock_held_common(&ret))
return ret;
return lock_is_held(&rcu_sched_lock_map) || !preemptible();
}
EXPORT_SYMBOL(rcu_read_lock_sched_held);
#endif
#ifndef CONFIG_TINY_RCU
/*
* Should expedited grace-period primitives always fall back to their
* non-expedited counterparts? Intended for use within RCU. Note
* that if the user specifies both rcu_expedited and rcu_normal, then
* rcu_normal wins. (Except during the time period during boot from
* when the first task is spawned until the rcu_set_runtime_mode()
* core_initcall() is invoked, at which point everything is expedited.)
*/
bool rcu_gp_is_normal(void)
{
return READ_ONCE(rcu_normal) &&
rcu_scheduler_active != RCU_SCHEDULER_INIT;
}
EXPORT_SYMBOL_GPL(rcu_gp_is_normal);
static atomic_t rcu_expedited_nesting = ATOMIC_INIT(1);
/*
* Should normal grace-period primitives be expedited? Intended for
* use within RCU. Note that this function takes the rcu_expedited
* sysfs/boot variable and rcu_scheduler_active into account as well
* as the rcu_expedite_gp() nesting. So looping on rcu_unexpedite_gp()
* until rcu_gp_is_expedited() returns false is a -really- bad idea.
*/
bool rcu_gp_is_expedited(void)
{
return rcu_expedited || atomic_read(&rcu_expedited_nesting);
}
EXPORT_SYMBOL_GPL(rcu_gp_is_expedited);
/**
* rcu_expedite_gp - Expedite future RCU grace periods
*
* After a call to this function, future calls to synchronize_rcu() and
* friends act as the corresponding synchronize_rcu_expedited() function
* had instead been called.
*/
void rcu_expedite_gp(void)
{
atomic_inc(&rcu_expedited_nesting);
}
EXPORT_SYMBOL_GPL(rcu_expedite_gp);
/**
* rcu_unexpedite_gp - Cancel prior rcu_expedite_gp() invocation
*
* Undo a prior call to rcu_expedite_gp(). If all prior calls to
* rcu_expedite_gp() are undone by a subsequent call to rcu_unexpedite_gp(),
* and if the rcu_expedited sysfs/boot parameter is not set, then all
* subsequent calls to synchronize_rcu() and friends will return to
* their normal non-expedited behavior.
*/
void rcu_unexpedite_gp(void)
{
atomic_dec(&rcu_expedited_nesting);
}
EXPORT_SYMBOL_GPL(rcu_unexpedite_gp);
static bool rcu_boot_ended __read_mostly;
/*
* Inform RCU of the end of the in-kernel boot sequence.
*/
void rcu_end_inkernel_boot(void)
{
rcu_unexpedite_gp();
if (rcu_normal_after_boot)
WRITE_ONCE(rcu_normal, 1);
rcu_boot_ended = true;
}
/*
* Let rcutorture know when it is OK to turn it up to eleven.
*/
bool rcu_inkernel_boot_has_ended(void)
{
return rcu_boot_ended;
}
EXPORT_SYMBOL_GPL(rcu_inkernel_boot_has_ended);
#endif /* #ifndef CONFIG_TINY_RCU */
/*
* Test each non-SRCU synchronous grace-period wait API. This is
* useful just after a change in mode for these primitives, and
* during early boot.
*/
void rcu_test_sync_prims(void)
{
if (!IS_ENABLED(CONFIG_PROVE_RCU))
return;
synchronize_rcu();
synchronize_rcu_expedited();
}
#if !defined(CONFIG_TINY_RCU) || defined(CONFIG_SRCU)
/*
* Switch to run-time mode once RCU has fully initialized.
*/
static int __init rcu_set_runtime_mode(void)
{
rcu_test_sync_prims();
rcu_scheduler_active = RCU_SCHEDULER_RUNNING;
kfree_rcu_scheduler_running();
rcu_test_sync_prims();
return 0;
}
core_initcall(rcu_set_runtime_mode);
#endif /* #if !defined(CONFIG_TINY_RCU) || defined(CONFIG_SRCU) */
#ifdef CONFIG_DEBUG_LOCK_ALLOC
static struct lock_class_key rcu_lock_key;
struct lockdep_map rcu_lock_map = {
.name = "rcu_read_lock",
.key = &rcu_lock_key,
.wait_type_outer = LD_WAIT_FREE,
.wait_type_inner = LD_WAIT_CONFIG, /* PREEMPT_RT implies PREEMPT_RCU */
};
EXPORT_SYMBOL_GPL(rcu_lock_map);
static struct lock_class_key rcu_bh_lock_key;
struct lockdep_map rcu_bh_lock_map = {
.name = "rcu_read_lock_bh",
.key = &rcu_bh_lock_key,
.wait_type_outer = LD_WAIT_FREE,
.wait_type_inner = LD_WAIT_CONFIG, /* PREEMPT_RT makes BH preemptible. */
};
EXPORT_SYMBOL_GPL(rcu_bh_lock_map);
static struct lock_class_key rcu_sched_lock_key;
struct lockdep_map rcu_sched_lock_map = {
.name = "rcu_read_lock_sched",
.key = &rcu_sched_lock_key,
.wait_type_outer = LD_WAIT_FREE,
.wait_type_inner = LD_WAIT_SPIN,
};
EXPORT_SYMBOL_GPL(rcu_sched_lock_map);
// Tell lockdep when RCU callbacks are being invoked.
static struct lock_class_key rcu_callback_key;
struct lockdep_map rcu_callback_map =
STATIC_LOCKDEP_MAP_INIT("rcu_callback", &rcu_callback_key);
EXPORT_SYMBOL_GPL(rcu_callback_map);
noinstr int notrace debug_lockdep_rcu_enabled(void)
{
return rcu_scheduler_active != RCU_SCHEDULER_INACTIVE && READ_ONCE(debug_locks) &&
current->lockdep_recursion == 0;
}
EXPORT_SYMBOL_GPL(debug_lockdep_rcu_enabled);
/**
* rcu_read_lock_held() - might we be in RCU read-side critical section?
*
* If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an RCU
* read-side critical section. In absence of CONFIG_DEBUG_LOCK_ALLOC,
* this assumes we are in an RCU read-side critical section unless it can
* prove otherwise. This is useful for debug checks in functions that
* require that they be called within an RCU read-side critical section.
*
* Checks debug_lockdep_rcu_enabled() to prevent false positives during boot
* and while lockdep is disabled.
*
* Note that rcu_read_lock() and the matching rcu_read_unlock() must
* occur in the same context, for example, it is illegal to invoke
* rcu_read_unlock() in process context if the matching rcu_read_lock()
* was invoked from within an irq handler.
*
* Note that rcu_read_lock() is disallowed if the CPU is either idle or
* offline from an RCU perspective, so check for those as well.
*/
int rcu_read_lock_held(void)
{
bool ret;
if (rcu_read_lock_held_common(&ret))
return ret;
return lock_is_held(&rcu_lock_map);
}
EXPORT_SYMBOL_GPL(rcu_read_lock_held);
/**
* rcu_read_lock_bh_held() - might we be in RCU-bh read-side critical section?
*
* Check for bottom half being disabled, which covers both the
* CONFIG_PROVE_RCU and not cases. Note that if someone uses
* rcu_read_lock_bh(), but then later enables BH, lockdep (if enabled)
* will show the situation. This is useful for debug checks in functions
* that require that they be called within an RCU read-side critical
* section.
*
* Check debug_lockdep_rcu_enabled() to prevent false positives during boot.
*
* Note that rcu_read_lock_bh() is disallowed if the CPU is either idle or
* offline from an RCU perspective, so check for those as well.
*/
int rcu_read_lock_bh_held(void)
{
bool ret;
if (rcu_read_lock_held_common(&ret))
return ret;
return in_softirq() || irqs_disabled();
}
EXPORT_SYMBOL_GPL(rcu_read_lock_bh_held);
int rcu_read_lock_any_held(void)
{
bool ret;
if (rcu_read_lock_held_common(&ret))
return ret;
if (lock_is_held(&rcu_lock_map) ||
lock_is_held(&rcu_bh_lock_map) ||
lock_is_held(&rcu_sched_lock_map))
return 1;
return !preemptible();
}
EXPORT_SYMBOL_GPL(rcu_read_lock_any_held);
#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
/**
* wakeme_after_rcu() - Callback function to awaken a task after grace period
* @head: Pointer to rcu_head member within rcu_synchronize structure
*
* Awaken the corresponding task now that a grace period has elapsed.
*/
void wakeme_after_rcu(struct rcu_head *head)
{
struct rcu_synchronize *rcu;
rcu = container_of(head, struct rcu_synchronize, head);
complete(&rcu->completion);
}
EXPORT_SYMBOL_GPL(wakeme_after_rcu);
void __wait_rcu_gp(bool checktiny, int n, call_rcu_func_t *crcu_array,
struct rcu_synchronize *rs_array)
{
int i;
int j;
/* Initialize and register callbacks for each crcu_array element. */
for (i = 0; i < n; i++) {
if (checktiny &&
(crcu_array[i] == call_rcu)) {
might_sleep();
continue;
}
for (j = 0; j < i; j++)
if (crcu_array[j] == crcu_array[i])
break;
if (j == i) {
init_rcu_head_on_stack(&rs_array[i].head);
init_completion(&rs_array[i].completion);
(crcu_array[i])(&rs_array[i].head, wakeme_after_rcu);
}
}
/* Wait for all callbacks to be invoked. */
for (i = 0; i < n; i++) {
if (checktiny &&
(crcu_array[i] == call_rcu))
continue;
for (j = 0; j < i; j++)
if (crcu_array[j] == crcu_array[i])
break;
if (j == i) {
wait_for_completion(&rs_array[i].completion);
destroy_rcu_head_on_stack(&rs_array[i].head);
}
}
}
EXPORT_SYMBOL_GPL(__wait_rcu_gp);
void finish_rcuwait(struct rcuwait *w)
{
rcu_assign_pointer(w->task, NULL);
__set_current_state(TASK_RUNNING);
}
EXPORT_SYMBOL_GPL(finish_rcuwait);
#ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
void init_rcu_head(struct rcu_head *head)
{
debug_object_init(head, &rcuhead_debug_descr);
}
EXPORT_SYMBOL_GPL(init_rcu_head);
void destroy_rcu_head(struct rcu_head *head)
{
debug_object_free(head, &rcuhead_debug_descr);
}
EXPORT_SYMBOL_GPL(destroy_rcu_head);
static bool rcuhead_is_static_object(void *addr)
{
return true;
}
/**
* init_rcu_head_on_stack() - initialize on-stack rcu_head for debugobjects
* @head: pointer to rcu_head structure to be initialized
*
* This function informs debugobjects of a new rcu_head structure that
* has been allocated as an auto variable on the stack. This function
* is not required for rcu_head structures that are statically defined or
* that are dynamically allocated on the heap. This function has no
* effect for !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds.
*/
void init_rcu_head_on_stack(struct rcu_head *head)
{
debug_object_init_on_stack(head, &rcuhead_debug_descr);
}
EXPORT_SYMBOL_GPL(init_rcu_head_on_stack);
/**
* destroy_rcu_head_on_stack() - destroy on-stack rcu_head for debugobjects
* @head: pointer to rcu_head structure to be initialized
*
* This function informs debugobjects that an on-stack rcu_head structure
* is about to go out of scope. As with init_rcu_head_on_stack(), this
* function is not required for rcu_head structures that are statically
* defined or that are dynamically allocated on the heap. Also as with
* init_rcu_head_on_stack(), this function has no effect for
* !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds.
*/
void destroy_rcu_head_on_stack(struct rcu_head *head)
{
debug_object_free(head, &rcuhead_debug_descr);
}
EXPORT_SYMBOL_GPL(destroy_rcu_head_on_stack);
const struct debug_obj_descr rcuhead_debug_descr = {
.name = "rcu_head",
.is_static_object = rcuhead_is_static_object,
};
EXPORT_SYMBOL_GPL(rcuhead_debug_descr);
#endif /* #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD */
#if defined(CONFIG_TREE_RCU) || defined(CONFIG_RCU_TRACE)
void do_trace_rcu_torture_read(const char *rcutorturename, struct rcu_head *rhp,
unsigned long secs,
unsigned long c_old, unsigned long c)
{
trace_rcu_torture_read(rcutorturename, rhp, secs, c_old, c);
}
EXPORT_SYMBOL_GPL(do_trace_rcu_torture_read);
#else
#define do_trace_rcu_torture_read(rcutorturename, rhp, secs, c_old, c) \
do { } while (0)
#endif
#if IS_ENABLED(CONFIG_RCU_TORTURE_TEST) || IS_MODULE(CONFIG_RCU_TORTURE_TEST)
/* Get rcutorture access to sched_setaffinity(). */
long rcutorture_sched_setaffinity(pid_t pid, const struct cpumask *in_mask)
{
int ret;
ret = sched_setaffinity(pid, in_mask);
WARN_ONCE(ret, "%s: sched_setaffinity() returned %d\n", __func__, ret);
return ret;
}
EXPORT_SYMBOL_GPL(rcutorture_sched_setaffinity);
#endif
#ifdef CONFIG_RCU_STALL_COMMON
int rcu_cpu_stall_ftrace_dump __read_mostly;
module_param(rcu_cpu_stall_ftrace_dump, int, 0644);
int rcu_cpu_stall_suppress __read_mostly; // !0 = suppress stall warnings.
EXPORT_SYMBOL_GPL(rcu_cpu_stall_suppress);
module_param(rcu_cpu_stall_suppress, int, 0644);
int rcu_cpu_stall_timeout __read_mostly = CONFIG_RCU_CPU_STALL_TIMEOUT;
module_param(rcu_cpu_stall_timeout, int, 0644);
int rcu_exp_cpu_stall_timeout __read_mostly = CONFIG_RCU_EXP_CPU_STALL_TIMEOUT;
module_param(rcu_exp_cpu_stall_timeout, int, 0644);
#endif /* #ifdef CONFIG_RCU_STALL_COMMON */
// Suppress boot-time RCU CPU stall warnings and rcutorture writer stall
// warnings. Also used by rcutorture even if stall warnings are excluded.
int rcu_cpu_stall_suppress_at_boot __read_mostly; // !0 = suppress boot stalls.
EXPORT_SYMBOL_GPL(rcu_cpu_stall_suppress_at_boot);
module_param(rcu_cpu_stall_suppress_at_boot, int, 0444);
#ifdef CONFIG_PROVE_RCU
/*
* Early boot self test parameters.
*/
static bool rcu_self_test;
module_param(rcu_self_test, bool, 0444);
static int rcu_self_test_counter;
static void test_callback(struct rcu_head *r)
{
rcu_self_test_counter++;
pr_info("RCU test callback executed %d\n", rcu_self_test_counter);
}
DEFINE_STATIC_SRCU(early_srcu);
static unsigned long early_srcu_cookie;
struct early_boot_kfree_rcu {
struct rcu_head rh;
};
static void early_boot_test_call_rcu(void)
{
static struct rcu_head head;
static struct rcu_head shead;
struct early_boot_kfree_rcu *rhp;
call_rcu(&head, test_callback);
if (IS_ENABLED(CONFIG_SRCU)) {
early_srcu_cookie = start_poll_synchronize_srcu(&early_srcu);
call_srcu(&early_srcu, &shead, test_callback);
}
rhp = kmalloc(sizeof(*rhp), GFP_KERNEL);
if (!WARN_ON_ONCE(!rhp))
kfree_rcu(rhp, rh);
}
void rcu_early_boot_tests(void)
{
pr_info("Running RCU self tests\n");
if (rcu_self_test)
early_boot_test_call_rcu();
rcu_test_sync_prims();
}
static int rcu_verify_early_boot_tests(void)
{
int ret = 0;
int early_boot_test_counter = 0;
if (rcu_self_test) {
early_boot_test_counter++;
rcu_barrier();
if (IS_ENABLED(CONFIG_SRCU)) {
early_boot_test_counter++;
srcu_barrier(&early_srcu);
WARN_ON_ONCE(!poll_state_synchronize_srcu(&early_srcu, early_srcu_cookie));
}
}
if (rcu_self_test_counter != early_boot_test_counter) {
WARN_ON(1);
ret = -1;
}
return ret;
}
late_initcall(rcu_verify_early_boot_tests);
#else
void rcu_early_boot_tests(void) {}
#endif /* CONFIG_PROVE_RCU */
#include "tasks.h"
#ifndef CONFIG_TINY_RCU
/*
* Print any significant non-default boot-time settings.
*/
void __init rcupdate_announce_bootup_oddness(void)
{
if (rcu_normal)
pr_info("\tNo expedited grace period (rcu_normal).\n");
else if (rcu_normal_after_boot)
pr_info("\tNo expedited grace period (rcu_normal_after_boot).\n");
else if (rcu_expedited)
pr_info("\tAll grace periods are expedited (rcu_expedited).\n");
if (rcu_cpu_stall_suppress)
pr_info("\tRCU CPU stall warnings suppressed (rcu_cpu_stall_suppress).\n");
if (rcu_cpu_stall_timeout != CONFIG_RCU_CPU_STALL_TIMEOUT)
pr_info("\tRCU CPU stall warnings timeout set to %d (rcu_cpu_stall_timeout).\n", rcu_cpu_stall_timeout);
rcu_tasks_bootup_oddness();
}
#endif /* #ifndef CONFIG_TINY_RCU */