linux-kernel - [PATCH 2/2] ftrace: skip special ftrace

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Message-Id: <20200728180554.65203-2-zhouchengming@bytedance.com>
Date:   Wed, 29 Jul 2020 02:05:54 +0800
From:   Chengming Zhou <zhouchengming@...edance.com>
To:     rostedt@...dmis.org, mingo@...hat.com, linux-kernel@...r.kernel.org
Cc:     zhouchengming@...edance.com, songmuchun@...edance.com
Subject: [PATCH 2/2] ftrace: skip special ftrace_ops when enable module

When enable module, we find all ftrace_ops referenced it on the
ftrace_ops_list. But FTRACE_OPS_FL_DIRECT and FTRACE_OPS_FL_IPMODIFY
flag are special, and should not be set automatically. So warn and
skip ftrace_ops that have these two flags.
Also check if only one ftrace_ops references the module, in which case
we can use trampoline as an optimization.

Signed-off-by: Chengming Zhou <zhouchengming@...edance.com>
Signed-off-by: Muchun Song <songmuchun@...edance.com>
---
 kernel/trace/ftrace.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index a3d141f53c9e..8c1d9e3daa67 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -6191,9 +6191,17 @@ static int referenced_filters(struct dyn_ftrace *rec)
 
 	for (ops = ftrace_ops_list; ops != &ftrace_list_end; ops = ops->next) {
 		if (ops_references_rec(ops, rec)) {
+			if (WARN_ON_ONCE(ops->flags & FTRACE_OPS_FL_DIRECT))
+				continue;
+			if (WARN_ON_ONCE(ops->flags & FTRACE_OPS_FL_IPMODIFY))
+				continue;
 			cnt++;
 			if (ops->flags & FTRACE_OPS_FL_SAVE_REGS)
 				rec->flags |= FTRACE_FL_REGS;
+			if (cnt == 1 && ops->trampoline)
+				rec->flags |= FTRACE_FL_TRAMP;
+			else
+				rec->flags &= ~FTRACE_FL_TRAMP;
 		}
 	}
 
-- 
2.20.1