[PATCH 1/1] rcu/tree: Drop the lock before entering to page allocator

* [PATCH 1/1] rcu/tree: Drop the lock before entering to page allocator
@ 2020-07-15 18:35 Uladzislau Rezki (Sony)
  2020-07-15 18:56 ` Sebastian Andrzej Siewior
  0 siblings, 1 reply; 20+ messages in thread
From: Uladzislau Rezki (Sony) @ 2020-07-15 18:35 UTC (permalink / raw)
  To: LKML, RCU, linux-mm, Paul E . McKenney
  Cc: Andrew Morton, Theodore Y . Ts'o, Matthew Wilcox,
	Joel Fernandes, Sebastian Andrzej Siewior, Uladzislau Rezki,
	Oleksiy Avramchenko

If the kernel is built with CONFIG_PROVE_RAW_LOCK_NESTING
option, the lockedp will complain about violation of the
nesting rules. It does the raw_spinlock vs. spinlock nesting
checks.

Internally the kfree_rcu() uses raw_spinlock_t whereas the
page allocator internally deals with spinlock_t to access
to its zones.

In order to prevent such vialation that is in question we
can drop the internal raw_spinlock_t before entering to
the page allocaor.

Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
---
 kernel/rcu/tree.c | 36 +++++++++++++++++++-----------------
 1 file changed, 19 insertions(+), 17 deletions(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 21c2fa5bd8c3..7469bd1e5c2c 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -3278,21 +3278,22 @@ static void kfree_rcu_monitor(struct work_struct *work)
 }
 
 static inline bool
-kvfree_call_rcu_add_ptr_to_bulk(struct kfree_rcu_cpu *krcp, void *ptr)
+add_ptr_to_bulk_krc_lock(struct kfree_rcu_cpu **krcp,
+	unsigned long *flags, void *ptr)
 {
 	struct kvfree_rcu_bulk_data *bnode;
 	int idx;
 
-	if (unlikely(!krcp->initialized))
+	*krcp = krc_this_cpu_lock(flags);
+	if (unlikely(!(*krcp)->initialized))
 		return false;
 
-	lockdep_assert_held(&krcp->lock);
 	idx = !!is_vmalloc_addr(ptr);
 
 	/* Check if a new block is required. */
-	if (!krcp->bkvhead[idx] ||
-			krcp->bkvhead[idx]->nr_records == KVFREE_BULK_MAX_ENTR) {
-		bnode = get_cached_bnode(krcp);
+	if (!(*krcp)->bkvhead[idx] ||
+			(*krcp)->bkvhead[idx]->nr_records == KVFREE_BULK_MAX_ENTR) {
+		bnode = get_cached_bnode(*krcp);
 		if (!bnode) {
 			/*
 			 * To keep this path working on raw non-preemptible
@@ -3306,6 +3307,9 @@ kvfree_call_rcu_add_ptr_to_bulk(struct kfree_rcu_cpu *krcp, void *ptr)
 			if (IS_ENABLED(CONFIG_PREEMPT_RT))
 				return false;
 
+			preempt_disable();
+			krc_this_cpu_unlock(*krcp, *flags);
+
 			/*
 			 * NOTE: For one argument of kvfree_rcu() we can
 			 * drop the lock and get the page in sleepable
@@ -3315,6 +3319,9 @@ kvfree_call_rcu_add_ptr_to_bulk(struct kfree_rcu_cpu *krcp, void *ptr)
 			 */
 			bnode = (struct kvfree_rcu_bulk_data *)
 				__get_free_page(GFP_NOWAIT | __GFP_NOWARN);
+
+			*krcp = krc_this_cpu_lock(flags);
+			preempt_enable();
 		}
 
 		/* Switch to emergency path. */
@@ -3323,15 +3330,15 @@ kvfree_call_rcu_add_ptr_to_bulk(struct kfree_rcu_cpu *krcp, void *ptr)
 
 		/* Initialize the new block. */
 		bnode->nr_records = 0;
-		bnode->next = krcp->bkvhead[idx];
+		bnode->next = (*krcp)->bkvhead[idx];
 
 		/* Attach it to the head. */
-		krcp->bkvhead[idx] = bnode;
+		(*krcp)->bkvhead[idx] = bnode;
 	}
 
 	/* Finally insert. */
-	krcp->bkvhead[idx]->records
-		[krcp->bkvhead[idx]->nr_records++] = ptr;
+	(*krcp)->bkvhead[idx]->records
+		[(*krcp)->bkvhead[idx]->nr_records++] = ptr;
 
 	return true;
 }
@@ -3369,24 +3376,19 @@ void kvfree_call_rcu(struct rcu_head *head, rcu_callback_t func)
 		ptr = (unsigned long *) func;
 	}
 
-	krcp = krc_this_cpu_lock(&flags);
-
 	// Queue the object but don't yet schedule the batch.
 	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);
-
-		// Mark as success and leave.
-		success = true;
-		goto unlock_return;
+		return;
 	}
 
 	/*
 	 * Under high memory pressure GFP_NOWAIT can fail,
 	 * in that case the emergency path is maintained.
 	 */
-	success = kvfree_call_rcu_add_ptr_to_bulk(krcp, ptr);
+	success = add_ptr_to_bulk_krc_lock(&krcp, &flags, ptr);
 	if (!success) {
 		if (head == NULL)
 			// Inline if kvfree_rcu(one_arg) call.
-- 
2.20.1


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