[PATCH bpf-next v2 2/3] bpf: Remove bpf trampoline selector

[Yafang Shao <laoar.shao@xxxxxxxxx>]

After commit e21aa341785c ("bpf: Fix fexit trampoline."), the selector
is only used to indicate how many times the bpf trampoline image are
updated and been displayed in the trampoline ksym name. After the
trampoline is freed, the selector will start from 0 again. So the
selector is a useless value to the user. We can remove it.
If the user want to check whether the bpf trampoline image has been updated
or not, the user can compare the address. Each time the trampoline image
is updated, the address will change consequently.

Jiri pointed out antoher issue that perf is still using the old name
"bpf_trampoline_%lu", so this change can fix the issue in perf.

Fixes: e21aa341785c ("bpf: Fix fexit trampoline.")
Signed-off-by: Yafang Shao <laoar.shao@xxxxxxxxx>
Cc: Song Liu <song@xxxxxxxxxx>
Cc: Jiri Olsa <olsajiri@xxxxxxxxx>
---
 include/linux/bpf.h     |  1 -
 kernel/bpf/trampoline.c | 11 ++++-------
 2 files changed, 4 insertions(+), 8 deletions(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 456f33b..36e4b2d 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -1125,7 +1125,6 @@ struct bpf_trampoline {
 	int progs_cnt[BPF_TRAMP_MAX];
 	/* Executable image of trampoline */
 	struct bpf_tramp_image *cur_image;
-	u64 selector;
 	struct module *mod;
 };
 
diff --git a/kernel/bpf/trampoline.c b/kernel/bpf/trampoline.c
index 2a3849c..78acf28 100644
--- a/kernel/bpf/trampoline.c
+++ b/kernel/bpf/trampoline.c
@@ -349,7 +349,7 @@ static void bpf_tramp_image_put(struct bpf_tramp_image *im)
 	call_rcu_tasks_trace(&im->rcu, __bpf_tramp_image_put_rcu_tasks);
 }
 
-static struct bpf_tramp_image *bpf_tramp_image_alloc(u64 key, u32 idx)
+static struct bpf_tramp_image *bpf_tramp_image_alloc(u64 key)
 {
 	struct bpf_tramp_image *im;
 	struct bpf_ksym *ksym;
@@ -376,7 +376,7 @@ static struct bpf_tramp_image *bpf_tramp_image_alloc(u64 key, u32 idx)
 
 	ksym = &im->ksym;
 	INIT_LIST_HEAD_RCU(&ksym->lnode);
-	snprintf(ksym->name, KSYM_NAME_LEN, "bpf_trampoline_%llu_%u", key, idx);
+	snprintf(ksym->name, KSYM_NAME_LEN, "bpf_trampoline_%llu", key);
 	bpf_image_ksym_add(image, ksym);
 	return im;
 
@@ -406,11 +406,10 @@ static int bpf_trampoline_update(struct bpf_trampoline *tr, bool lock_direct_mut
 		err = unregister_fentry(tr, tr->cur_image->image);
 		bpf_tramp_image_put(tr->cur_image);
 		tr->cur_image = NULL;
-		tr->selector = 0;
 		goto out;
 	}
 
-	im = bpf_tramp_image_alloc(tr->key, tr->selector);
+	im = bpf_tramp_image_alloc(tr->key);
 	if (IS_ERR(im)) {
 		err = PTR_ERR(im);
 		goto out;
@@ -447,8 +446,7 @@ static int bpf_trampoline_update(struct bpf_trampoline *tr, bool lock_direct_mut
 
 	set_memory_rox((long)im->image, 1);
 
-	WARN_ON(tr->cur_image && tr->selector == 0);
-	WARN_ON(!tr->cur_image && tr->selector);
+	WARN_ON(tr->cur_image && total == 0);
 	if (tr->cur_image)
 		/* progs already running at this address */
 		err = modify_fentry(tr, tr->cur_image->image, im->image, lock_direct_mutex);
@@ -478,7 +476,6 @@ static int bpf_trampoline_update(struct bpf_trampoline *tr, bool lock_direct_mut
 	if (tr->cur_image)
 		bpf_tramp_image_put(tr->cur_image);
 	tr->cur_image = im;
-	tr->selector++;
 out:
 	/* If any error happens, restore previous flags */
 	if (err)
-- 
1.8.3.1