[PATCH 1/1] lib/stackdepot: print disabled message only if truly disabled

[PATCH 1/1] lib/stackdepot: print disabled message only if truly disabled

[andrey.konovalov]

From: Andrey Konovalov <andreyknvl@google.com>

Currently, if stack_depot_disable=off is passed to the kernel
command-line after stack_depot_disable=on, stack depot prints a message
that it is disabled, while it is actually enabled.

Fix this by moving printing the disabled message to
stack_depot_early_init. Place it before the
__stack_depot_early_init_requested check, so that the message is printed
even if early stack depot init has not been requested.

Also drop the stack_table = NULL assignment from disable_stack_depot,
as stack_table is NULL by default.

Fixes: e1fdc403349c ("lib: stackdepot: add support to disable stack depot")
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
---
 lib/stackdepot.c | 24 +++++++++++++++---------
 1 file changed, 15 insertions(+), 9 deletions(-)

diff --git a/lib/stackdepot.c b/lib/stackdepot.c
index 2f5aa851834e..0eeaef4f2523 100644
--- a/lib/stackdepot.c
+++ b/lib/stackdepot.c
@@ -101,14 +101,7 @@ static int next_pool_required = 1;
 
 static int __init disable_stack_depot(char *str)
 {
-	int ret;
-
-	ret = kstrtobool(str, &stack_depot_disabled);
-	if (!ret && stack_depot_disabled) {
-		pr_info("disabled\n");
-		stack_table = NULL;
-	}
-	return 0;
+	return kstrtobool(str, &stack_depot_disabled);
 }
 early_param("stack_depot_disable", disable_stack_depot);
 
@@ -130,6 +123,15 @@ int __init stack_depot_early_init(void)
 		return 0;
 	__stack_depot_early_init_passed = true;
 
+	/*
+	 * Print disabled message even if early init has not been requested:
+	 * stack_depot_init() will not print one.
+	 */
+	if (stack_depot_disabled) {
+		pr_info("disabled\n");
+		return 0;
+	}
+
 	/*
 	 * If KASAN is enabled, use the maximum order: KASAN is frequently used
 	 * in fuzzing scenarios, which leads to a large number of different
@@ -138,7 +140,11 @@ int __init stack_depot_early_init(void)
 	if (kasan_enabled() && !stack_bucket_number_order)
 		stack_bucket_number_order = STACK_BUCKET_NUMBER_ORDER_MAX;
 
-	if (!__stack_depot_early_init_requested || stack_depot_disabled)
+	/*
+	 * Check if early init has been requested after setting
+	 * stack_bucket_number_order: stack_depot_init() uses its value.
+	 */
+	if (!__stack_depot_early_init_requested)
 		return 0;
 
 	/*
-- 
2.25.1

Re: [PATCH 1/1] lib/stackdepot: print disabled message only if truly disabled

[Andrey Konovalov]

On Fri, Oct 27, 2023 at 2:54 PM Marco Elver <elver@google.com> wrote:
>
> stack_bucket_number_order seems like a redundant variable, that should
> at least be __ro_after_init. All code that does "if
> (stack_bucket_number_order) ..." could just do "if (kasan_enabled())
> ..." and use STACK_BUCKET_NUMBER_ORDER_MAX constant directly instead.
>
> The code here could be simplified if it was removed. No idea why it
> was introduced in the first place. I think f9987921cb541 introduced it
> and there it said "complemented with a boot-time kernel parameter",
> but that never happened.
>
> So I'd be in favor of removing that variable, which will also simplify
> this code.

On the first thought, this seems reasonable with the current code.

On the second though, I think I will soon add a command-line parameter
to allow controlling how much memory is used for the stack depot hash
table.

I propose we keep the code as is for now, but I've taken a note to
either drop this variable or mark it as __ro_after_init when
implementing memory bounding controls for stack depot.

Thanks!