[PATCH v2] lib/vsprintf: Make no_hash_pointers take effect early

[PATCH v2] lib/vsprintf: Make no_hash_pointers take effect early

[Kaitao Cheng]

From: Kaitao Cheng <chengkaitao@kylinos.cn>

The no_hash_pointers boot parameter is now handled as an alias for
hash_pointers=never. However, hash_pointers=never only records the
selected mode during early parameter parsing, and no_hash_pointers is
not updated until hash_pointers_finalize() runs later from SLUB init.

This leaves a window during very early boot where %p output is still
hashed even though the user explicitly requested unhashed pointers with
no_hash_pointers or hash_pointers=never.

Set no_hash_pointers as soon as the "never" mode is parsed. The later
hash_pointers_finalize() call still keeps the final policy decision in
one place, but explicit requests to disable pointer hashing now take
effect for early boot users too.

In Documentation/admin-guide/kernel-parameters.txt, the descriptions
of both no_hash_pointers and hash_pointers= are already marked as
[KNL,EARLY], which match the current semantics.

Signed-off-by: Kaitao Cheng <chengkaitao@kylinos.cn>
---
Changes in v2 (Andy Shevchenko):
- Add a description of the kernel documentation to the commit log.

Link to v1:
https://lore.kernel.org/all/20260610124525.59110-1-kaitao.cheng@linux.dev/
---
 lib/vsprintf.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index 4221e95701f9..9d35c84f6c49 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -2361,6 +2361,7 @@ static int __init hash_pointers_mode_parse(char *str)
 	} else if (strcmp(str, "never") == 0) {
 		pr_info("Hash pointers mode set to never.\n");
 		hash_pointers_mode = HASH_PTR_NEVER;
+		no_hash_pointers = true;
 	} else if (strcmp(str, "always") == 0) {
 		pr_info("Hash pointers mode set to always.\n");
 		hash_pointers_mode = HASH_PTR_ALWAYS;
-- 
2.43.0

Re: [PATCH v2] lib/vsprintf: Make no_hash_pointers take effect early

[Petr Mladek]

On Fri 2026-06-12 11:06:42, Kaitao Cheng wrote:
> From: Kaitao Cheng <chengkaitao@kylinos.cn>
> 
> The no_hash_pointers boot parameter is now handled as an alias for
> hash_pointers=never. However, hash_pointers=never only records the
> selected mode during early parameter parsing, and no_hash_pointers is
> not updated until hash_pointers_finalize() runs later from SLUB init.
> 
> This leaves a window during very early boot where %p output is still
> hashed even though the user explicitly requested unhashed pointers with
> no_hash_pointers or hash_pointers=never.
> 
> Set no_hash_pointers as soon as the "never" mode is parsed. The later
> hash_pointers_finalize() call still keeps the final policy decision in
> one place, but explicit requests to disable pointer hashing now take
> effect for early boot users too.
> 
> In Documentation/admin-guide/kernel-parameters.txt, the descriptions
> of both no_hash_pointers and hash_pointers= are already marked as
> [KNL,EARLY], which match the current semantics.
> 
> --- a/lib/vsprintf.c
> +++ b/lib/vsprintf.c
> @@ -2361,6 +2361,7 @@ static int __init hash_pointers_mode_parse(char *str)
>  	} else if (strcmp(str, "never") == 0) {
>  		pr_info("Hash pointers mode set to never.\n");
>  		hash_pointers_mode = HASH_PTR_NEVER;
> +		no_hash_pointers = true;
>  	} else if (strcmp(str, "always") == 0) {
>  		pr_info("Hash pointers mode set to always.\n");
>  		hash_pointers_mode = HASH_PTR_ALWAYS;

Sashiko AI has a good point that we should reset no_hash_pointers to
false by default. It would handle the situation when the parameter
is passed more times on the command line. Aka, the last parameter
wins. See
https://sashiko.dev/#/patchset/20260612030642.14239-1-kaitao.cheng%40linux.dev

It is not a big deal. But let's do it right when touching this.

Otherwise, the patch makes sense and looks good to me.

Best Regards,
Petr