linux-kernel - Re: [PATCH] alloc_tag: remove sysctl prefix from mem

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Message-ID: <20260114072507.163364-1-ranxiaokai627@163.com>
Date: Wed, 14 Jan 2026 07:25:00 +0000
From: ranxiaokai627@....com
To: surenb@...gle.com
Cc: Liam.Howlett@...cle.com,
	akpm@...ux-foundation.org,
	corbet@....net,
	david@...nel.org,
	kent.overstreet@...ux.dev,
	linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-mm@...ck.org,
	lorenzo.stoakes@...cle.com,
	mhocko@...e.com,
	ran.xiaokai@....com.cn,
	ranxiaokai627@....com,
	rppt@...nel.org,
	vbabka@...e.cz
Subject: Re: [PATCH] alloc_tag: remove sysctl prefix from mem_profiling boot parameter

>On Mon, Jan 12, 2026 at 7:50 PM Kent Overstreet
><kent.overstreet@...ux.dev> wrote:
>>
>> On Tue, Jan 13, 2026 at 03:27:35AM +0000, ranxiaokai627@....com wrote:
>> > >On Fri, Jan 09, 2026 at 06:24:19AM +0000, ranxiaokai627@....com wrote:
>> > >> From: Ran Xiaokai <ran.xiaokai@....com.cn>
>> > >>
>> > >> Boot parameters prefixed with "sysctl." are processed separately
>> > >> during the final stage of system initialization via kernel_init()->
>> > >> do_sysctl_args(). Since mem_profiling support should be parsed
>> > >> in early boot stage, it is unsuitable for centralized handling
>> > >> in do_sysctl_args().
>> > >> Also, when CONFIG_MEM_ALLOC_PROFILING_DEBUG is enabled,
>> > >> the sysctl.vm.mem_profiling entry is not writable and will cause
>> > >> a warning. To prevent duplicate processing of sysctl.vm.mem_profiling,
>> > >> rename the boot parameter to "mem_profiling".
>> > >>
>> > >> Signed-off-by: Ran Xiaokai <ran.xiaokai@....com.cn>
>> > >
>> > >How was this observed/detected?
>> >
>> > Actually no kernel bug or funtional defect was observed through testing.
>> > Via code reading, i found after commit [1],
>> > boot parameters prefixed with sysctl is processed redundantly.
>
>I was able to reproduce the warning by enabling
>CONFIG_MEM_ALLOC_PROFILING,
>CONFIG_MEM_ALLOC_PROFILING_ENABLED_BY_DEFAULT,
>CONFIG_MEM_ALLOC_PROFILING_DEBUG, CONFIG_SYSCTL and setting
>CONFIG_CMDLINE="1".
>The fix I posted eliminates that warning. Ran, you can post my
>suggestion yourself with me as Suggested-by or I can post it with you
>as Reported-by. Let me know your preference.

I think this version is better.

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

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.

Signed-off-by: Ran Xiaokai <ran.xiaokai@....com.cn>
Suggested-by: Suren Baghdasaryan <surenb@...gle.
---
 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


>> When bcachefs was in the kernel, I spent an inordinate amount of time in
>> code reviews trying to convince people that yes, they really do need to
>> be testing their code.
>>
>> Strangely enough, I have never had this issue with project contributors
>> who did not come to the project by way of the kernel community... :)