Re: [PATCH v2] ftrace: Synchronize the initialization of ftrace_ops
From: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Date: 2026-09-04 00:47:16
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On Wed, 2 Sep 2026 09:55:01 -0400 Steven Rostedt [off-list ref] wrote:
From: Steven Rostedt <rostedt@goodmis.org> There's some internal state that ftrace_ops needs to have set, but since it can be declared outside of the ftrace.c code, it calls ftrace_ops_init() on the ops in every global function. The issue is that if two tasks call it on the same ops at the same time it is possible to have the initialization of one corrupt the initialization of the other call. Create a ops_mutex to use to synchronize every initialization of the ftrace_ops. The mutex is taken within checking the ftrace_ops flag that states it was initializied but the flag is checked again after the mutex has been taken. Checking first outside the mutex allows it to shortcut having to take the mutex. But then the check needs to be done again after the mute is taken in case of races.
Looks good to me. Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org> Thanks,
quoted hunk ↗ jump to hunk
Cc: stable@vger.kernel.org Fixes: f04f24fb7e48d ("ftrace, kprobes: Fix a deadlock on ftrace_regex_lock") Reported-by: sashiko-bot@kernel.org Close: https://lore.kernel.org/all/20260829025528.49A831F000E9@smtp.kernel.org/ (local) Signed-off-by: Steven Rostedt <rostedt@goodmis.org> --- Changes since v1: https://patch.msgid.link/20260901202020.09a1119a@robin - Added smp_load_acquire() and smp_store_release() to make sure that the flags value that is compared is really updated after the code has been initialized. (Sashiko) kernel/trace/ftrace.c | 13 +++++++++++-- 1 file changed, 11 insertions(+), 2 deletions(-)diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c index c7cf36f2dd7b..53d5db60bfa5 100644 --- a/kernel/trace/ftrace.c +++ b/kernel/trace/ftrace.c@@ -75,6 +75,8 @@ .func_hash = &opsname.local_hash, \ .local_hash.regex_lock = __MUTEX_INITIALIZER(opsname.local_hash.regex_lock), \ .subop_list = LIST_HEAD_INIT(opsname.subop_list), +/* Used only to synchronize the initialization of ftrace_ops */ +static DEFINE_MUTEX(ops_mutex); #else #define INIT_OPS_HASH(opsname) #endif@@ -159,11 +161,18 @@ const struct ftrace_ops ftrace_nop_ops = { static inline void ftrace_ops_init(struct ftrace_ops *ops) { #ifdef CONFIG_DYNAMIC_FTRACE - if (!(ops->flags & FTRACE_OPS_FL_INITIALIZED)) { + unsigned long flags = smp_load_acquire(&ops->flags); + + if (!(flags & FTRACE_OPS_FL_INITIALIZED)) { + guard(mutex)(&ops_mutex); + /* Could have been initialized before lock taken */ + if (unlikely(ops->flags & FTRACE_OPS_FL_INITIALIZED)) + return; mutex_init(&ops->local_hash.regex_lock); INIT_LIST_HEAD(&ops->subop_list); ops->func_hash = &ops->local_hash; - ops->flags |= FTRACE_OPS_FL_INITIALIZED; + flags = ops->flags | FTRACE_OPS_FL_INITIALIZED; + smp_store_release(&ops->flags, flags); } #endif }-- 2.53.0
-- Masami Hiramatsu (Google) [off-list ref]