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fgraph: Still initialize idle shadow stacks when starting

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BugLink: https://bugs.launchpad.net/bugs/2102266

commit cc252bb592638e0f7aea40d580186c36d89526b8 upstream.

A bug was discovered where the idle shadow stacks were not initialized
for offline CPUs when starting function graph tracer, and when they came
online they were not traced due to the missing shadow stack. To fix
this, the idle task shadow stack initialization was moved to using the
CPU hotplug callbacks. But it removed the initialization when the
function graph was enabled. The problem here is that the hotplug
callbacks are called when the CPUs come online, but the idle shadow
stack initialization only happens if function graph is currently
active. This caused the online CPUs to not get their shadow stack
initialized.

The idle shadow stack initialization still needs to be done when the
function graph is registered, as they will not be allocated if function
graph is not registered.

Cc: stable@vger.kernel.org
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Link: https://lore.kernel.org/20241211135335.094ba282@batman.local.home
Fixes: 2c02f7375e65 ("fgraph: Use CPU hotplug mechanism to initialize idle shadow stacks")
Reported-by: Linus Walleij <linus.walleij@linaro.org>
Tested-by: Linus Walleij <linus.walleij@linaro.org>
Closes: https://lore.kernel.org/all/CACRpkdaTBrHwRbbrphVy-=SeDz6MSsXhTKypOtLrTQ+DgGAOcQ@mail.gmail.com/
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
[koichiroden: adjusted context due to missing commit:
42675b723b48 ("function_graph: Convert ret_stack to a series of longs")]
Signed-off-by: Koichiro Den <koichiro.den@canonical.com>
Signed-off-by: Mehmet Basaran <mehmet.basaran@canonical.com>
This commit is contained in:
Steven Rostedt
2025-03-14 12:03:09 +09:00
committed by Mehmet Basaran
parent c46e55a64d
commit af7ebb5fa0
1 changed files with 7 additions and 1 deletions
Download Patch File Download Diff File Expand all files Collapse all files
kernel/trace/fgraph.c
+7 -1
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@@ -600,7 +600,7 @@ void ftrace_graph_exit_task(struct task_struct *t)
static int start_graph_tracing(void)
{
struct ftrace_ret_stack **ret_stack_list;
int ret;
int ret, cpu;
ret_stack_list = kmalloc_array(FTRACE_RETSTACK_ALLOC_SIZE,
sizeof(struct ftrace_ret_stack *),
@@ -609,6 +609,12 @@ static int start_graph_tracing(void)
if (!ret_stack_list)
return -ENOMEM;
/* The cpu_boot init_task->ret_stack will never be freed */
for_each_online_cpu(cpu) {
if (!idle_task(cpu)->ret_stack)
ftrace_graph_init_idle_task(idle_task(cpu), cpu);
}
do {
ret = alloc_retstack_tasklist(ret_stack_list);
} while (ret == -EAGAIN);