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

[Andrii Nakryiko]

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 <and...@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