+ mm-codetag-clear-tags-before-swap.patch added to mm-hotfixes-unstable branch

+ mm-codetag-clear-tags-before-swap.patch added to mm-hotfixes-unstable branch

[Andrew Morton]

The patch titled
     Subject: mm/codetag: clear tags before swap
has been added to the -mm mm-hotfixes-unstable branch.  Its filename is
     mm-codetag-clear-tags-before-swap.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-codetag-clear-tags-before-swap.patch

This patch will later appear in the mm-hotfixes-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: David Wang <00107082@163.com>
Subject: mm/codetag: clear tags before swap
Date: Fri, 13 Dec 2024 09:33:32 +0800

When CONFIG_MEM_ALLOC_PROFILING_DEBUG is set, kernel WARN would be
triggered when calling __alloc_tag_ref_set() during swap:

	alloc_tag was not cleared (got tag for mm/filemap.c:1951)
	WARNING: CPU: 0 PID: 816 at ./include/linux/alloc_tag.h...

Clear code tags before swap can fix the warning. And this patch also fix
a potential invalid address dereference in alloc_tag_add_check() when
CONFIG_MEM_ALLOC_PROFILING_DEBUG is set and ref->ct is CODETAG_EMPTY,
which is defined as ((void *)1).

Link: https://lkml.kernel.org/r/20241213013332.89910-1-00107082@163.com
Fixes: 51f43d5d82ed ("mm/codetag: swap tags when migrate pages")
Signed-off-by: David Wang <00107082@163.com>
Reported-by: kernel test robot <oliver.sang@intel.com>
Closes: https://lore.kernel.org/oe-lkp/202412112227.df61ebb-lkp@intel.com
Acked-by: Suren Baghdasaryan <surenb@google.com>
Cc: Kent Overstreet <kent.overstreet@linux.dev>
Cc: Yu Zhao <yuzhao@google.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 include/linux/alloc_tag.h |    2 +-
 lib/alloc_tag.c           |    7 +++++++
 2 files changed, 8 insertions(+), 1 deletion(-)

--- a/include/linux/alloc_tag.h~mm-codetag-clear-tags-before-swap
+++ a/include/linux/alloc_tag.h
@@ -140,7 +140,7 @@ static inline struct alloc_tag_counters
 #ifdef CONFIG_MEM_ALLOC_PROFILING_DEBUG
 static inline void alloc_tag_add_check(union codetag_ref *ref, struct alloc_tag *tag)
 {
-	WARN_ONCE(ref && ref->ct,
+	WARN_ONCE(ref && ref->ct && !is_codetag_empty(ref),
 		  "alloc_tag was not cleared (got tag for %s:%u)\n",
 		  ref->ct->filename, ref->ct->lineno);
 
--- a/lib/alloc_tag.c~mm-codetag-clear-tags-before-swap
+++ a/lib/alloc_tag.c
@@ -209,6 +209,13 @@ void pgalloc_tag_swap(struct folio *new,
 		return;
 	}
 
+	/*
+	 * Clear tag references to avoid debug warning when using
+	 * __alloc_tag_ref_set() with non-empty reference.
+	 */
+	set_codetag_empty(&ref_old);
+	set_codetag_empty(&ref_new);
+
 	/* swap tags */
 	__alloc_tag_ref_set(&ref_old, tag_new);
 	update_page_tag_ref(handle_old, &ref_old);
_

Patches currently in -mm which might be from 00107082@163.com are

mm-codetag-clear-tags-before-swap.patch