Re: [Linux-kernel-mentees] [PATCH] tracing: Annotate ftrace_graph_hash pointer with __rcu
From: Joel Fernandes <hidden>
Date: 2020-02-03 16:43:14
Also in:
lkml
On Sat, Feb 01, 2020 at 12:57:04PM +0530, Amol Grover wrote:
quoted hunk ↗ jump to hunk
Fix following instances of sparse error kernel/trace/ftrace.c:5664:29: error: incompatible types in comparison kernel/trace/ftrace.c:5785:21: error: incompatible types in comparison kernel/trace/ftrace.c:5864:36: error: incompatible types in comparison kernel/trace/ftrace.c:5866:25: error: incompatible types in comparison Use rcu_dereference_protected to access the __rcu annotated pointer. Signed-off-by: Amol Grover <redacted> --- kernel/trace/ftrace.c | 2 +- kernel/trace/trace.h | 9 ++++++--- 2 files changed, 7 insertions(+), 4 deletions(-)diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c index 9bf1f2cd515e..959ded08dc13 100644 --- a/kernel/trace/ftrace.c +++ b/kernel/trace/ftrace.c@@ -5596,7 +5596,7 @@ static const struct file_operations ftrace_notrace_fops = { static DEFINE_MUTEX(graph_lock); -struct ftrace_hash *ftrace_graph_hash = EMPTY_HASH; +struct ftrace_hash __rcu *ftrace_graph_hash = EMPTY_HASH; struct ftrace_hash *ftrace_graph_notrace_hash = EMPTY_HASH; enum graph_filter_type {diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h index 63bf60f79398..97dad3326020 100644 --- a/kernel/trace/trace.h +++ b/kernel/trace/trace.h@@ -950,22 +950,25 @@ extern void __trace_graph_return(struct trace_array *tr, unsigned long flags, int pc); #ifdef CONFIG_DYNAMIC_FTRACE -extern struct ftrace_hash *ftrace_graph_hash; +extern struct ftrace_hash __rcu *ftrace_graph_hash; extern struct ftrace_hash *ftrace_graph_notrace_hash; static inline int ftrace_graph_addr(struct ftrace_graph_ent *trace) { unsigned long addr = trace->func; int ret = 0; + struct ftrace_hash *hash; preempt_disable_notrace(); - if (ftrace_hash_empty(ftrace_graph_hash)) { + hash = rcu_dereference_protected(ftrace_graph_hash, !preemptible());
I think you can use rcu_dereference_sched() here? That way no need to pass !preemptible. A preempt-disabled section is an RCU "sched flavor" section. Flavors are consolidated in the backend, but in the front end the dereference API still do have flavors. thanks, - Joel
+
+ if (ftrace_hash_empty(hash)) {
ret = 1;
goto out;
}
- if (ftrace_lookup_ip(ftrace_graph_hash, addr)) {
+ if (ftrace_lookup_ip(hash, addr)) {
/*
* This needs to be cleared on the return functions
--
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