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Subject[PATCH 07/18] rcu/tree: Simplify debug_objects handling
Date
In order to prepare for future changes for headless RCU support, make the
debug_objects handling in kfree_rcu use the final 'pointer' value of the
object, instead of depending on the head.

Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
---
kernel/rcu/tree.c | 30 +++++++++++++-----------------
1 file changed, 13 insertions(+), 17 deletions(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 3fb19ea039912..95d1f5e20d5ec 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -2825,7 +2825,6 @@ struct kfree_rcu_bulk_data {
unsigned long nr_records;
void *records[KFREE_BULK_MAX_ENTR];
struct kfree_rcu_bulk_data *next;
- struct rcu_head *head_free_debug;
};

/**
@@ -2875,11 +2874,11 @@ struct kfree_rcu_cpu {
static DEFINE_PER_CPU(struct kfree_rcu_cpu, krc);

static __always_inline void
-debug_rcu_head_unqueue_bulk(struct rcu_head *head)
+debug_rcu_bhead_unqueue(struct kfree_rcu_bulk_data *bhead)
{
#ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
- for (; head; head = head->next)
- debug_rcu_head_unqueue(head);
+ for (int i = 0; i < bhead->nr_records; i++)
+ debug_rcu_head_unqueue((struct rcu_head *)(bhead->records[i]));
#endif
}

@@ -2909,7 +2908,7 @@ static void kfree_rcu_work(struct work_struct *work)
for (; bhead; bhead = bnext) {
bnext = bhead->next;

- debug_rcu_head_unqueue_bulk(bhead->head_free_debug);
+ debug_rcu_bhead_unqueue(bhead);

rcu_lock_acquire(&rcu_callback_map);
trace_rcu_invoke_kfree_bulk_callback(rcu_state.name,
@@ -2931,14 +2930,15 @@ static void kfree_rcu_work(struct work_struct *work)
*/
for (; head; head = next) {
unsigned long offset = (unsigned long)head->func;
+ void *ptr = (void *)head - offset;

next = head->next;
- debug_rcu_head_unqueue(head);
+ debug_rcu_head_unqueue((struct rcu_head *)ptr);
rcu_lock_acquire(&rcu_callback_map);
trace_rcu_invoke_kvfree_callback(rcu_state.name, head, offset);

if (!WARN_ON_ONCE(!__is_kvfree_rcu_offset(offset)))
- kvfree((void *)head - offset);
+ kvfree(ptr);

rcu_lock_release(&rcu_callback_map);
cond_resched_tasks_rcu_qs();
@@ -3062,18 +3062,11 @@ kfree_call_rcu_add_ptr_to_bulk(struct kfree_rcu_cpu *krcp,
/* Initialize the new block. */
bnode->nr_records = 0;
bnode->next = krcp->bhead;
- bnode->head_free_debug = NULL;

/* Attach it to the head. */
krcp->bhead = bnode;
}

-#ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
- head->func = func;
- head->next = krcp->bhead->head_free_debug;
- krcp->bhead->head_free_debug = head;
-#endif
-
/* Finally insert. */
krcp->bhead->records[krcp->bhead->nr_records++] =
(void *) head - (unsigned long) func;
@@ -3097,14 +3090,17 @@ void kvfree_call_rcu(struct rcu_head *head, rcu_callback_t func)
{
unsigned long flags;
struct kfree_rcu_cpu *krcp;
+ void *ptr;

local_irq_save(flags); // For safely calling this_cpu_ptr().
krcp = this_cpu_ptr(&krc);
if (krcp->initialized)
spin_lock(&krcp->lock);

+ ptr = (void *)head - (unsigned long)func;
+
// Queue the object but don't yet schedule the batch.
- if (debug_rcu_head_queue(head)) {
+ if (debug_rcu_head_queue(ptr)) {
// Probable double kfree_rcu(), just leak.
WARN_ONCE(1, "%s(): Double-freed call. rcu_head %p\n",
__func__, head);
@@ -3121,8 +3117,8 @@ void kvfree_call_rcu(struct rcu_head *head, rcu_callback_t func)
* Under high memory pressure GFP_NOWAIT can fail,
* in that case the emergency path is maintained.
*/
- if (is_vmalloc_addr((void *) head - (unsigned long) func) ||
- !kfree_call_rcu_add_ptr_to_bulk(krcp, head, func)) {
+ if (is_vmalloc_addr(ptr) ||
+ !kfree_call_rcu_add_ptr_to_bulk(krcp, head, func)) {
head->func = func;
head->next = krcp->head;
krcp->head = head;
--
2.26.0.rc2.310.g2932bb562d-goog
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