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Message-Id: <20250528034712.138701-17-dongml2@chinatelecom.cn>
Date: Wed, 28 May 2025 11:47:03 +0800
From: Menglong Dong <menglong8.dong@...il.com>
To: alexei.starovoitov@...il.com,
rostedt@...dmis.org,
jolsa@...nel.org
Cc: bpf@...r.kernel.org,
Menglong Dong <dongml2@...natelecom.cn>,
linux-kernel@...r.kernel.org
Subject: [PATCH bpf-next 16/25] ftrace: supporting replace direct ftrace_ops
Introduce the function replace_ftrace_direct(). This is used to replace
the direct ftrace_ops for a function, and will be used in the next patch.
Let's call the origin ftrace_ops A, and the new ftrace_ops B. First, we
register B directly, and the callback of the functions in A and B will
fallback to the ftrace_ops_list case.
Then, we modify the address of the entry in the direct_functions to
B->direct_call, and remove it from A. This will update the dyn_rec and
make the functions call b->direct_call directly. If no function in
A->filter_hash, just unregister it.
So a record can have more than one direct ftrace_ops, and we need check
if there is any direct ops for the record before remove the
FTRACE_OPS_FL_DIRECT in __ftrace_hash_rec_update().
Signed-off-by: Menglong Dong <dongml2@...natelecom.cn>
---
include/linux/ftrace.h | 8 ++++
kernel/trace/ftrace.c | 87 +++++++++++++++++++++++++++++++++++++++++-
2 files changed, 93 insertions(+), 2 deletions(-)
diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
index 40727d3f125d..1d162e331e99 100644
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h
@@ -528,6 +528,9 @@ void ftrace_stub_direct_tramp(void);
int reset_ftrace_direct_ips(struct ftrace_ops *ops, unsigned long *ips,
unsigned int cnt);
+int replace_ftrace_direct(struct ftrace_ops *ops, struct ftrace_ops *src_ops,
+ unsigned long addr);
+
#else
struct ftrace_ops;
static inline unsigned long ftrace_find_rec_direct(unsigned long ip)
@@ -556,6 +559,11 @@ static inline int reset_ftrace_direct_ips(struct ftrace_ops *ops, unsigned long
{
return -ENODEV;
}
+static inline int replace_ftrace_direct(struct ftrace_ops *ops, struct ftrace_ops *src_ops,
+ unsigned long addr)
+{
+ return -ENODEV;
+}
/*
* This must be implemented by the architecture.
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 5b6b74ea4c20..7f2313e4c3d9 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -1727,6 +1727,24 @@ static bool skip_record(struct dyn_ftrace *rec)
!(rec->flags & FTRACE_FL_ENABLED);
}
+static struct ftrace_ops *
+ftrace_find_direct_ops_any_other(struct dyn_ftrace *rec, struct ftrace_ops *op_exclude)
+{
+ struct ftrace_ops *op;
+ unsigned long ip = rec->ip;
+
+ do_for_each_ftrace_op(op, ftrace_ops_list) {
+
+ if (op == op_exclude || !(op->flags & FTRACE_OPS_FL_DIRECT))
+ continue;
+
+ if (hash_contains_ip(ip, op->func_hash))
+ return op;
+ } while_for_each_ftrace_op(op);
+
+ return NULL;
+}
+
/*
* This is the main engine to the ftrace updates to the dyn_ftrace records.
*
@@ -1831,8 +1849,10 @@ static bool __ftrace_hash_rec_update(struct ftrace_ops *ops,
* function, then that function should no longer
* be direct.
*/
- if (ops->flags & FTRACE_OPS_FL_DIRECT)
- rec->flags &= ~FTRACE_FL_DIRECT;
+ if (ops->flags & FTRACE_OPS_FL_DIRECT) {
+ if (!ftrace_find_direct_ops_any_other(rec, ops))
+ rec->flags &= ~FTRACE_FL_DIRECT;
+ }
/*
* If the rec had REGS enabled and the ops that is
@@ -6033,6 +6053,69 @@ int register_ftrace_direct(struct ftrace_ops *ops, unsigned long addr)
}
EXPORT_SYMBOL_GPL(register_ftrace_direct);
+int replace_ftrace_direct(struct ftrace_ops *ops, struct ftrace_ops *src_ops,
+ unsigned long addr)
+{
+ struct ftrace_hash *hash;
+ struct ftrace_func_entry *entry, *iter;
+ int err = -EBUSY, size, count;
+
+ if (ops->func || ops->trampoline)
+ return -EINVAL;
+ if (!(ops->flags & FTRACE_OPS_FL_INITIALIZED))
+ return -EINVAL;
+ if (ops->flags & FTRACE_OPS_FL_ENABLED)
+ return -EINVAL;
+
+ hash = ops->func_hash->filter_hash;
+ if (ftrace_hash_empty(hash))
+ return -EINVAL;
+
+ mutex_lock(&direct_mutex);
+
+ ops->func = call_direct_funcs;
+ ops->flags = MULTI_FLAGS;
+ ops->trampoline = FTRACE_REGS_ADDR;
+ ops->direct_call = addr;
+
+ err = register_ftrace_function_nolock(ops);
+ if (err)
+ goto out_unlock;
+
+ hash = ops->func_hash->filter_hash;
+ size = 1 << hash->size_bits;
+ for (int i = 0; i < size; i++) {
+ hlist_for_each_entry(iter, &hash->buckets[i], hlist) {
+ entry = __ftrace_lookup_ip(direct_functions, iter->ip);
+ if (!entry) {
+ err = -ENOENT;
+ goto out_unlock;
+ }
+ WRITE_ONCE(entry->direct, addr);
+ /* remove the ip from the hash, and this will make the trampoline
+ * be called directly.
+ */
+ count = src_ops->func_hash->filter_hash->count;
+ if (count <= 1) {
+ if (WARN_ON_ONCE(!count))
+ continue;
+ err = __unregister_ftrace_direct(src_ops, src_ops->direct_call,
+ true);
+ } else {
+ err = ftrace_set_filter_ip(src_ops, iter->ip, 1, 0);
+ }
+ if (err)
+ goto out_unlock;
+ }
+ }
+
+out_unlock:
+ mutex_unlock(&direct_mutex);
+
+ return err;
+}
+EXPORT_SYMBOL_GPL(replace_ftrace_direct);
+
/**
* unregister_ftrace_direct - Remove calls to custom trampoline
* previously registered by register_ftrace_direct for @ops object.
--
2.39.5
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