[PATCH 08/12] uprobes: split uprobe allocation and uprobes_tree insertion steps

[Andrii Nakryiko <andrii@kernel.org>]

Now we are ready to split alloc-and-insert coupled step into two
separate phases.

First, we allocate and prepare all potentially-to-be-inserted uprobe
instances, assuming corresponding uprobes are not yet in uprobes_tree.
This is needed so that we don't do memory allocations under
uprobes_treelock (once we batch locking for each step).

Second, we insert new uprobes or reuse already existing ones into
uprobes_tree. Any uprobe that turned out to be not necessary is
immediately freed, as there are no other references to it.

This concludes preparations that make uprobes_register_batch() ready to
batch and optimize locking per each phase.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
---
 kernel/events/uprobes.c | 21 ++++++++++++---------
 1 file changed, 12 insertions(+), 9 deletions(-)

diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index ebd8511b6eb2..5e98e179d47d 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -1270,9 +1270,8 @@ int uprobe_register_batch(struct inode *inode, int cnt,
 			return -EINVAL;
 	}
 
+	/* pre-allocate new uprobe instances */
 	for (i = 0; i < cnt; i++) {
-		struct uprobe *cur_uprobe;
-
 		uc = get_uprobe_consumer(i, ctx);
 
 		uprobe = kzalloc(sizeof(struct uprobe), GFP_KERNEL);
@@ -1289,6 +1288,15 @@ int uprobe_register_batch(struct inode *inode, int cnt,
 		RB_CLEAR_NODE(&uprobe->rb_node);
 		atomic64_set(&uprobe->ref, 1);
 
+		uc->uprobe = uprobe;
+	}
+
+	for (i = 0; i < cnt; i++) {
+		struct uprobe *cur_uprobe;
+
+		uc = get_uprobe_consumer(i, ctx);
+		uprobe = uc->uprobe;
+
 		/* add to uprobes_tree, sorted on inode:offset */
 		cur_uprobe = insert_uprobe(uprobe);
 		/* a uprobe exists for this inode:offset combination */
@@ -1296,15 +1304,12 @@ int uprobe_register_batch(struct inode *inode, int cnt,
 			if (cur_uprobe->ref_ctr_offset != uprobe->ref_ctr_offset) {
 				ref_ctr_mismatch_warn(cur_uprobe, uprobe);
 				put_uprobe(cur_uprobe);
-				kfree(uprobe);
 				ret = -EINVAL;
 				goto cleanup_uprobes;
 			}
 			kfree(uprobe);
-			uprobe = cur_uprobe;
+			uc->uprobe = cur_uprobe;
 		}
-
-		uc->uprobe = uprobe;
 	}
 
 	for (i = 0; i < cnt; i++) {
@@ -1318,10 +1323,8 @@ int uprobe_register_batch(struct inode *inode, int cnt,
 			__uprobe_unregister(uprobe, uc);
 		up_write(&uprobe->register_rwsem);
 
-		if (ret) {
-			put_uprobe(uprobe);
+		if (ret)
 			goto cleanup_unreg;
-		}
 	}
 
 	return 0;
-- 
2.43.0