fgraph: Allocate ret_stack_list with proper size

The ret_stack_list is an array of ret_stack shadow stacks for the function
graph usage. When the first function graph is enabled, all tasks in the
system get a shadow stack. The ret_stack_list is a 32 element array of
pointers to these shadow stacks. It allocates the shadow stack in batches
(32 stacks at a time), assigns them to running tasks, and continues until
all tasks are covered.

When the function graph shadow stack changed from an array of
ftrace_ret_stack structures to an array of longs, the allocation of
ret_stack_list went from allocating an array of 32 elements to just a
block defined by SHADOW_STACK_SIZE. Luckily, that's defined as PAGE_SIZE
and is much more than enough to hold 32 pointers. But it is way overkill
for the amount needed to allocate.

Change the allocation of ret_stack_list back to a kcalloc() of
FTRACE_RETSTACK_ALLOC_SIZE pointers.

Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Link: https://lore.kernel.org/20241018215212.23f13f40@rorschach
Fixes: 42675b723b484 ("function_graph: Convert ret_stack to a series of longs")
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

diff --git a/kernel/trace/fgraph.c b/kernel/trace/fgraph.c
index 43f4e3f57438b4213909d909b90a83feb6ad3108..41e7a15dcb50c4bf99a1620ddae7ba0562aa95ca 100644 (file)
--- a/kernel/trace/fgraph.c
+++ b/kernel/trace/fgraph.c
@@ -1162,7 +1162,8 @@ static int start_graph_tracing(void)
        unsigned long **ret_stack_list;
        int ret;
 
-       ret_stack_list = kmalloc(SHADOW_STACK_SIZE, GFP_KERNEL);
+       ret_stack_list = kcalloc(FTRACE_RETSTACK_ALLOC_SIZE,
+                                sizeof(*ret_stack_list), GFP_KERNEL);
 
        if (!ret_stack_list)
                return -ENOMEM;