[PATCH v2] alloc_tag: fix rw permission issue when handling boot parameter

[PATCH v2] alloc_tag: fix rw permission issue when handling boot parameter

[ranxiaokai627]

From: Ran Xiaokai <ran.xiaokai@zte.com.cn>

Boot parameters prefixed with "sysctl." are processed
during the final stage of system initialization via kernel_init()->
do_sysctl_args(). When CONFIG_MEM_ALLOC_PROFILING_DEBUG is enabled,
the sysctl.vm.mem_profiling entry is not writable and will cause
a warning.

Before run_init_process(), system initialization executes in kernel
thread context. Use current->mm to distinguish sysctl writes during
do_sysctl_args() from user-space triggered ones.

And when the proc_handler is from do_sysctl_args(), always return success
because the same value was already set by setup_early_mem_profiling()
and this eliminates a permission denied warning.

Suggested-by: Suren Baghdasaryan <surenb@google.com>
Acked-by: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Ran Xiaokai <ran.xiaokai@zte.com.cn>
---
 lib/alloc_tag.c | 22 ++++++++++++++++------
 1 file changed, 16 insertions(+), 6 deletions(-)

diff --git a/lib/alloc_tag.c b/lib/alloc_tag.c
index 846a5b5b44a4..00ae4673a271 100644
--- a/lib/alloc_tag.c
+++ b/lib/alloc_tag.c
@@ -776,8 +776,22 @@ EXPORT_SYMBOL(page_alloc_tagging_ops);
 static int proc_mem_profiling_handler(const struct ctl_table *table, int write,
 				      void *buffer, size_t *lenp, loff_t *ppos)
 {
-	if (!mem_profiling_support && write)
-		return -EINVAL;
+	if (write) {
+		/*
+		 * Call from do_sysctl_args() which is a no-op since the same
+		 * value was already set by setup_early_mem_profiling.
+		 * Return success to avoid warnings from do_sysctl_args().
+		 */
+		if (!current->mm)
+			return 0;
+
+#ifdef CONFIG_MEM_ALLOC_PROFILING_DEBUG
+		/* User can't toggle profiling while debugging */
+		return -EACCES;
+#endif
+		if (!mem_profiling_support)
+			return -EINVAL;
+	}
 
 	return proc_do_static_key(table, write, buffer, lenp, ppos);
 }
@@ -787,11 +801,7 @@ static const struct ctl_table memory_allocation_profiling_sysctls[] = {
 	{
 		.procname	= "mem_profiling",
 		.data		= &mem_alloc_profiling_key,
-#ifdef CONFIG_MEM_ALLOC_PROFILING_DEBUG
-		.mode		= 0444,
-#else
 		.mode		= 0644,
-#endif
 		.proc_handler	= proc_mem_profiling_handler,
 	},
 };
-- 
2.25.1

Re: [PATCH v2] alloc_tag: fix rw permission issue when handling boot parameter

[Andrew Morton]

On Thu, 15 Jan 2026 03:15:36 +0000 ranxiaokai627@163.com wrote:

> From: Ran Xiaokai <ran.xiaokai@zte.com.cn>
> 
> Boot parameters prefixed with "sysctl." are processed
> during the final stage of system initialization via kernel_init()->
> do_sysctl_args(). When CONFIG_MEM_ALLOC_PROFILING_DEBUG is enabled,
> the sysctl.vm.mem_profiling entry is not writable and will cause
> a warning.

This sounds strange.  Why would setting a Kconfig debug thing disable
alteration of a runtime control? 
Documentation/mm/allocation-profiling.rst provided no hint.

> Before run_init_process(), system initialization executes in kernel
> thread context. Use current->mm to distinguish sysctl writes during
> do_sysctl_args() from user-space triggered ones.
> 
> And when the proc_handler is from do_sysctl_args(), always return success
> because the same value was already set by setup_early_mem_profiling()
> and this eliminates a permission denied warning.
> 
> Suggested-by: Suren Baghdasaryan <surenb@google.com>
> Acked-by: Suren Baghdasaryan <surenb@google.com>
> Signed-off-by: Ran Xiaokai <ran.xiaokai@zte.com.cn>

Should we backport it?