[07/18] rcu/tree: Simplify debug_objects handling

Commit Message

Joel Fernandes March 30, 2020, 2:32 a.m. UTC

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) <[e-mail]>
---
 kernel/rcu/tree.c | 30 +++++++++++++-----------------
 1 file changed, 13 insertions(+), 17 deletions(-)

Comments

kernel test robot March 30, 2020, 7 a.m. UTC | #1

Hi "Joel,

Thank you for the patch! Yet something to improve:

[auto build test ERROR on rcu/dev]
[also build test ERROR on rcu/rcu/next next-20200327]
[cannot apply to linus/master linux/master v5.6]
[if your patch is applied to the wrong git tree, please drop us a note to help
improve the system. BTW, we also suggest to use '--base' option to specify the
base tree in git format-patch, please see https://stackoverflow.com/a/37406982]

url:    https://github.com/0day-ci/linux/commits/Joel-Fernandes-Google/kfree_rcu-improvements-for-rcu-dev/20200330-113719
base:   https://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git dev
config: i386-allyesconfig (attached as .config)
compiler: gcc-7 (Debian 7.5.0-5) 7.5.0
reproduce:
        # save the attached .config to linux build tree
        make ARCH=i386 

If you fix the issue, kindly add following tag
Reported-by: kbuild test robot <[e-mail]>

All errors (new ones prefixed by >>):

   kernel/rcu/tree.c: In function 'debug_rcu_bhead_unqueue':
>> kernel/rcu/tree.c:2880:2: error: 'for' loop initial declarations are only allowed in C99 or C11 mode
     for (int i = 0; i < bhead->nr_records; i++)
     ^~~
   kernel/rcu/tree.c:2880:2: note: use option -std=c99, -std=gnu99, -std=c11 or -std=gnu11 to compile your code

vim +/for +2880 kernel/rcu/tree.c

  2875	
  2876	static __always_inline void
  2877	debug_rcu_bhead_unqueue(struct kfree_rcu_bulk_data *bhead)
  2878	{
  2879	#ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
> 2880		for (int i = 0; i < bhead->nr_records; i++)
  2881			debug_rcu_head_unqueue((struct rcu_head *)(bhead->records[i]));
  2882	#endif
  2883	}
  2884	

---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/[e-mail]

Joel Fernandes March 30, 2020, 6:42 p.m. UTC | #2

On Mon, Mar 30, 2020 at 03:00:18PM +0800, kbuild test robot wrote:
> Hi "Joel,
> 
> Thank you for the patch! Yet something to improve:
> 
> [auto build test ERROR on rcu/dev]
> [also build test ERROR on rcu/rcu/next next-20200327]
> [cannot apply to linus/master linux/master v5.6]
> [if your patch is applied to the wrong git tree, please drop us a note to help
> improve the system. BTW, we also suggest to use '--base' option to specify the
> base tree in git format-patch, please see https://stackoverflow.com/a/37406982]

Should have run allmodconfig, this is a slightly older patch and did not see
a problem earlier in prior testing.

Will make the trivial fix now and update my tree, thanks!

 - Joel

Patch

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;