[PATCH v2 09/12] uprobes: batch uprobes_treelock during registration

[Andrii Nakryiko <andrii@kernel.org>]

Now that we have a good separate of each registration step, take
uprobes_treelock just once for relevant registration step, and then
process all relevant uprobes in one go.

Even if writer lock introduces a relatively large delay (as might happen
with per-CPU RW semaphore), this will keep overall batch attachment
reasonably fast.

We teach put_uprobe(), though __put_uprobe() helper, to optionally take
or not uprobes_treelock, to accommodate this pattern.

With these changes we don't need insert_uprobe() operation that
unconditionally takes uprobes_treelock, so get rid of it, leaving only
lower-level __insert_uprobe() helper.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
---
 kernel/events/uprobes.c | 45 +++++++++++++++++++++--------------------
 1 file changed, 23 insertions(+), 22 deletions(-)

diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index 128677ffe662..ced85284bbf4 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -665,7 +665,7 @@ static void uprobe_free_rcu(struct rcu_head *rcu)
 	kfree(uprobe);
 }
 
-static void put_uprobe(struct uprobe *uprobe)
+static void __put_uprobe(struct uprobe *uprobe, bool tree_locked)
 {
 	s64 v;
 
@@ -683,7 +683,8 @@ static void put_uprobe(struct uprobe *uprobe)
 	if (unlikely((u32)v == 0)) {
 		bool destroy;
 
-		write_lock(&uprobes_treelock);
+		if (!tree_locked)
+			write_lock(&uprobes_treelock);
 		/*
 		 * We might race with find_uprobe()->__get_uprobe() executed
 		 * from inside read-locked uprobes_treelock, which can bump
@@ -706,7 +707,8 @@ static void put_uprobe(struct uprobe *uprobe)
 		destroy = atomic64_read(&uprobe->ref) == v;
 		if (destroy && uprobe_is_active(uprobe))
 			rb_erase(&uprobe->rb_node, &uprobes_tree);
-		write_unlock(&uprobes_treelock);
+		if (!tree_locked)
+			write_unlock(&uprobes_treelock);
 
 		/*
 		 * Beyond here we don't need RCU protection, we are either the
@@ -745,6 +747,11 @@ static void put_uprobe(struct uprobe *uprobe)
 	rcu_read_unlock_trace();
 }
 
+static void put_uprobe(struct uprobe *uprobe)
+{
+	__put_uprobe(uprobe, false);
+}
+
 static __always_inline
 int uprobe_cmp(const struct inode *l_inode, const loff_t l_offset,
 	       const struct uprobe *r)
@@ -844,21 +851,6 @@ static struct uprobe *__insert_uprobe(struct uprobe *uprobe)
 	return u;
 }
 
-/*
- * Acquire uprobes_treelock and insert uprobe into uprobes_tree
- * (or reuse existing one, see __insert_uprobe() comments above).
- */
-static struct uprobe *insert_uprobe(struct uprobe *uprobe)
-{
-	struct uprobe *u;
-
-	write_lock(&uprobes_treelock);
-	u = __insert_uprobe(uprobe);
-	write_unlock(&uprobes_treelock);
-
-	return u;
-}
-
 static void
 ref_ctr_mismatch_warn(struct uprobe *cur_uprobe, struct uprobe *uprobe)
 {
@@ -1318,6 +1310,8 @@ int uprobe_register_batch(struct inode *inode, int cnt,
 		uc->uprobe = uprobe;
 	}
 
+	ret = 0;
+	write_lock(&uprobes_treelock);
 	for (i = 0; i < cnt; i++) {
 		struct uprobe *cur_uprobe;
 
@@ -1325,19 +1319,24 @@ int uprobe_register_batch(struct inode *inode, int cnt,
 		uprobe = uc->uprobe;
 
 		/* add to uprobes_tree, sorted on inode:offset */
-		cur_uprobe = insert_uprobe(uprobe);
+		cur_uprobe = __insert_uprobe(uprobe);
 		/* a uprobe exists for this inode:offset combination */
 		if (cur_uprobe != uprobe) {
 			if (cur_uprobe->ref_ctr_offset != uprobe->ref_ctr_offset) {
 				ref_ctr_mismatch_warn(cur_uprobe, uprobe);
-				put_uprobe(cur_uprobe);
+
+				__put_uprobe(cur_uprobe, true);
 				ret = -EINVAL;
-				goto cleanup_uprobes;
+				goto unlock_treelock;
 			}
 			kfree(uprobe);
 			uc->uprobe = cur_uprobe;
 		}
 	}
+unlock_treelock:
+	write_unlock(&uprobes_treelock);
+	if (ret)
+		goto cleanup_uprobes;
 
 	for (i = 0; i < cnt; i++) {
 		uc = get_uprobe_consumer(i, ctx);
@@ -1367,13 +1366,15 @@ int uprobe_register_batch(struct inode *inode, int cnt,
 	}
 cleanup_uprobes:
 	/* put all the successfully allocated/reused uprobes */
+	write_lock(&uprobes_treelock);
 	for (i = 0; i < cnt; i++) {
 		uc = get_uprobe_consumer(i, ctx);
 
 		if (uc->uprobe)
-			put_uprobe(uc->uprobe);
+			__put_uprobe(uc->uprobe, true);
 		uc->uprobe = NULL;
 	}
+	write_unlock(&uprobes_treelock);
 	return ret;
 }
 
-- 
2.43.0