linux-kernel - [PATCH bpf v2] ftrace: fix incorrect hash size in register_ftrace

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Message-Id: <20250413014444.36724-1-dongml2@chinatelecom.cn>
Date: Sun, 13 Apr 2025 09:44:44 +0800
From: Menglong Dong <menglong8.dong@...il.com>
To: rostedt@...dmis.org
Cc: mhiramat@...nel.org,
	mark.rutland@....com,
	mathieu.desnoyers@...icios.com,
	linux-kernel@...r.kernel.org,
	linux-trace-kernel@...r.kernel.org,
	bpf@...r.kernel.org,
	Menglong Dong <dongml2@...natelecom.cn>
Subject: [PATCH bpf v2] ftrace: fix incorrect hash size in register_ftrace_direct()

The maximum of the ftrace hash bits is made fls(32) in
register_ftrace_direct(), which seems illogical. So, we fix it by making
the max hash bits FTRACE_HASH_MAX_BITS instead.

Fixes: d05cb470663a ("ftrace: Fix modification of direct_function hash while in use")
Signed-off-by: Menglong Dong <dongml2@...natelecom.cn>
---
v2:
- thanks for Steven's advice, we fix the problem by making the max hash
  bits FTRACE_HASH_MAX_BITS instead.
---
 kernel/trace/ftrace.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 1a48aedb5255..d153ad13e0e0 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -5914,9 +5914,10 @@ int register_ftrace_direct(struct ftrace_ops *ops, unsigned long addr)
 
 	/* Make a copy hash to place the new and the old entries in */
 	size = hash->count + direct_functions->count;
-	if (size > 32)
-		size = 32;
-	new_hash = alloc_ftrace_hash(fls(size));
+	size = fls(size);
+	if (size > FTRACE_HASH_MAX_BITS)
+		size = FTRACE_HASH_MAX_BITS;
+	new_hash = alloc_ftrace_hash(size);
 	if (!new_hash)
 		goto out_unlock;
 
-- 
2.39.5