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Message-ID: <20170607143659.29013dd3@gandalf.local.home>
Date: Wed, 7 Jun 2017 14:36:59 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Chunyan Zhang <zhang.chunyan@...aro.org>
Cc: mingo@...hat.com, linux-kernel@...r.kernel.org,
zhang.lyra@...il.com
Subject: Re: [RESEND PATCH v2] trace: fix the errors caused by incompatible
type of RCU variables
On Wed, 7 Jun 2017 16:12:51 +0800
Chunyan Zhang <zhang.chunyan@...aro.org> wrote:
> The variables which are processed by RCU functions should be annotated
> as RCU, otherwise sparse will report the errors like below:
>
> "error: incompatible types in comparison expression (different
> address spaces)"
>
> Signed-off-by: Chunyan Zhang <zhang.chunyan@...aro.org>
Hi,
> ---
>
> Changes in v2:
> * Addressed Steven's comments
> - Use rcu_dereference_protected() instead of rcu_dereference_raw_notrace()
> * Rebased on v4.12-rc1
>
> include/linux/ftrace.h | 6 +++---
> include/linux/trace_events.h | 2 +-
> kernel/trace/ftrace.c | 42 ++++++++++++++++++++++++++++--------------
> kernel/trace/trace.h | 6 +++---
> 4 files changed, 35 insertions(+), 21 deletions(-)
>
> diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
> index 473f088..056395c7 100644
> --- a/include/linux/ftrace.h
> +++ b/include/linux/ftrace.h
> @@ -142,8 +142,8 @@ enum {
> #ifdef CONFIG_DYNAMIC_FTRACE
> /* The hash used to know what functions callbacks trace */
> struct ftrace_ops_hash {
> - struct ftrace_hash *notrace_hash;
> - struct ftrace_hash *filter_hash;
> + struct ftrace_hash __rcu *notrace_hash;
> + struct ftrace_hash __rcu *filter_hash;
> struct mutex regex_lock;
> };
>
> @@ -165,7 +165,7 @@ static inline void ftrace_free_init_mem(void) { }
> */
> struct ftrace_ops {
> ftrace_func_t func;
> - struct ftrace_ops *next;
> + struct ftrace_ops __rcu *next;
> unsigned long flags;
> void *private;
> ftrace_func_t saved_func;
> diff --git a/include/linux/trace_events.h b/include/linux/trace_events.h
> index a556805..89f7bd5d 100644
> --- a/include/linux/trace_events.h
> +++ b/include/linux/trace_events.h
> @@ -327,7 +327,7 @@ enum {
> struct trace_event_file {
> struct list_head list;
> struct trace_event_call *event_call;
> - struct event_filter *filter;
> + struct event_filter __rcu *filter;
> struct dentry *dir;
> struct trace_array *tr;
> struct trace_subsystem_dir *system;
> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> index 39dca4e..116742b 100644
> --- a/kernel/trace/ftrace.c
> +++ b/kernel/trace/ftrace.c
> @@ -113,7 +113,8 @@ static int ftrace_disabled __read_mostly;
>
> static DEFINE_MUTEX(ftrace_lock);
>
> -static struct ftrace_ops *ftrace_ops_list __read_mostly = &ftrace_list_end;
> +static struct ftrace_ops __rcu *
> + ftrace_ops_list __read_mostly = &ftrace_list_end;
I may fix this myself, but newlines like the above is IMHO uglier than
going over 80 characters. I much rather keep it on one line.
> ftrace_func_t ftrace_trace_function __read_mostly = ftrace_stub;
> static struct ftrace_ops global_ops;
>
> @@ -169,8 +170,11 @@ int ftrace_nr_registered_ops(void)
>
> mutex_lock(&ftrace_lock);
>
> - for (ops = ftrace_ops_list;
> - ops != &ftrace_list_end; ops = ops->next)
> + for (ops = rcu_dereference_protected(ftrace_ops_list,
> + lockdep_is_held(&ftrace_lock));
> + ops != &ftrace_list_end;
> + ops = rcu_dereference_protected(ops->next,
> + lockdep_is_held(&ftrace_lock)))
> cnt++;
>
> mutex_unlock(&ftrace_lock);
> @@ -275,10 +279,11 @@ static void update_ftrace_function(void)
> * If there's only one ftrace_ops registered, the ftrace_ops_list
> * will point to the ops we want.
> */
> - set_function_trace_op = ftrace_ops_list;
> + set_function_trace_op = rcu_dereference_protected(ftrace_ops_list,
> + lockdep_is_held(&ftrace_lock));
>
> /* If there's no ftrace_ops registered, just call the stub function */
> - if (ftrace_ops_list == &ftrace_list_end) {
> + if (set_function_trace_op == &ftrace_list_end) {
Slight change of code, but shouldn't have any affect on the flow.
> func = ftrace_stub;
>
> /*
> @@ -286,7 +291,8 @@ static void update_ftrace_function(void)
> * recursion safe and not dynamic and the arch supports passing ops,
> * then have the mcount trampoline call the function directly.
> */
> - } else if (ftrace_ops_list->next == &ftrace_list_end) {
> + } else if (rcu_dereference_protected(ftrace_ops_list->next,
> + lockdep_is_held(&ftrace_lock)) == &ftrace_list_end) {
> func = ftrace_ops_get_list_func(ftrace_ops_list);
>
> } else {
> @@ -348,9 +354,11 @@ int using_ftrace_ops_list_func(void)
> return ftrace_trace_function == ftrace_ops_list_func;
> }
>
> -static void add_ftrace_ops(struct ftrace_ops **list, struct ftrace_ops *ops)
> +static void add_ftrace_ops(struct ftrace_ops __rcu **list,
> + struct ftrace_ops *ops)
> {
> - ops->next = *list;
> + rcu_assign_pointer(ops->next, *list);
> +
> /*
> * We are entering ops into the list but another
> * CPU might be walking that list. We need to make sure
> @@ -360,7 +368,8 @@ static void add_ftrace_ops(struct ftrace_ops **list, struct ftrace_ops *ops)
> rcu_assign_pointer(*list, ops);
> }
>
> -static int remove_ftrace_ops(struct ftrace_ops **list, struct ftrace_ops *ops)
> +static int remove_ftrace_ops(struct ftrace_ops __rcu **list,
> + struct ftrace_ops *ops)
> {
> struct ftrace_ops **p;
>
> @@ -368,7 +377,10 @@ static int remove_ftrace_ops(struct ftrace_ops **list, struct ftrace_ops *ops)
> * If we are removing the last function, then simply point
> * to the ftrace_stub.
> */
> - if (*list == ops && ops->next == &ftrace_list_end) {
> + if (rcu_dereference_protected(*list,
> + lockdep_is_held(&ftrace_lock)) == ops &&
> + rcu_dereference_protected(ops->next,
> + lockdep_is_held(&ftrace_lock)) == &ftrace_list_end) {
> *list = &ftrace_list_end;
> return 0;
> }
> @@ -1513,8 +1525,8 @@ ftrace_ops_test(struct ftrace_ops *ops, unsigned long ip, void *regs)
> return 0;
> #endif
>
> - hash.filter_hash = rcu_dereference_raw_notrace(ops->func_hash->filter_hash);
> - hash.notrace_hash = rcu_dereference_raw_notrace(ops->func_hash->notrace_hash);
> + rcu_assign_pointer(hash.filter_hash, ops->func_hash->filter_hash);
> + rcu_assign_pointer(hash.notrace_hash, ops->func_hash->notrace_hash);
>
> if (hash_contains_ip(ip, &hash))
> ret = 1;
> @@ -2784,7 +2796,8 @@ static int ftrace_shutdown(struct ftrace_ops *ops, int command)
> * If there's no more ops registered with ftrace, run a
> * sanity check to make sure all rec flags are cleared.
> */
> - if (ftrace_ops_list == &ftrace_list_end) {
> + if (rcu_dereference_protected(ftrace_ops_list,
> + lockdep_is_held(&ftrace_lock)) == &ftrace_list_end) {
> struct ftrace_page *pg;
> struct dyn_ftrace *rec;
>
> @@ -6122,7 +6135,8 @@ ftrace_enable_sysctl(struct ctl_table *table, int write,
> if (ftrace_enabled) {
>
> /* we are starting ftrace again */
> - if (ftrace_ops_list != &ftrace_list_end)
> + if (rcu_dereference_protected(ftrace_ops_list,
> + lockdep_is_held(&ftrace_lock)) != &ftrace_list_end)
> update_ftrace_function();
>
> ftrace_startup_sysctl();
> diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
> index 291a1bc..60b26b4 100644
> --- a/kernel/trace/trace.h
> +++ b/kernel/trace/trace.h
> @@ -1183,9 +1183,9 @@ struct ftrace_event_field {
> struct event_filter {
> int n_preds; /* Number assigned */
> int a_preds; /* allocated */
> - struct filter_pred *preds;
> - struct filter_pred *root;
> - char *filter_string;
> + struct filter_pred __rcu *preds;
> + struct filter_pred __rcu *root;
> + char *filter_string;
> };
>
> struct event_subsystem {
So far looks fine. I'll run it through my tests and see if it triggers
any lockdep issues.
-- Steve
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