+ mm-make-vm_area_struct-anon_name-field-rcu-safe.patch added to mm-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: mm: make vm_area_struct anon_name field RCU-safe
has been added to the -mm mm-unstable branch.  Its filename is
     mm-make-vm_area_struct-anon_name-field-rcu-safe.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-make-vm_area_struct-anon_name-field-rcu-safe.patch

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

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------------------------------------------------------
From: Suren Baghdasaryan <surenb@google.com>
Subject: mm: make vm_area_struct anon_name field RCU-safe
Date: Sun, 21 Jan 2024 23:13:22 -0800

For lockless /proc/pid/maps reading we have to ensure all the fields used
when generating the output are RCU-safe.  The only pointer fields in
vm_area_struct which are used to generate that file's output are vm_file
and anon_name.  vm_file is RCU-safe but anon_name is not.  Make anon_name
RCU-safe as well.

Link: https://lkml.kernel.org/r/20240122071324.2099712-1-surenb@google.com
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Andrei Vagin <avagin@google.com>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Ben Wolsieffer <ben.wolsieffer@hefring.com>
Cc: Casey Schaufler <casey@schaufler-ca.com>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Dave Chinner <dchinner@redhat.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Lorenzo Stoakes <lstoakes@gmail.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Muhammad Usama Anjum <usama.anjum@collabora.com>
Cc: Paul E. McKenney <paulmck@kernel.org>
Cc: Peter Xu <peterx@redhat.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Sidhartha Kumar <sidhartha.kumar@oracle.com>
Cc: T.J. Alumbaugh <talumbau@google.com>
Cc: Vishal Moola (Oracle) <vishal.moola@gmail.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Xingui Yang <yangxingui@huawei.com>
Cc: Yu Zhao <yuzhao@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 include/linux/mm_inline.h |   10 +++++++++-
 include/linux/mm_types.h  |    3 ++-
 mm/madvise.c              |   30 ++++++++++++++++++++++++++----
 3 files changed, 37 insertions(+), 6 deletions(-)

--- a/include/linux/mm_inline.h~mm-make-vm_area_struct-anon_name-field-rcu-safe
+++ a/include/linux/mm_inline.h
@@ -389,7 +389,7 @@ static inline void dup_anon_vma_name(str
 	struct anon_vma_name *anon_name = anon_vma_name(orig_vma);
 
 	if (anon_name)
-		new_vma->anon_name = anon_vma_name_reuse(anon_name);
+		rcu_assign_pointer(new_vma->anon_name, anon_vma_name_reuse(anon_name));
 }
 
 static inline void free_anon_vma_name(struct vm_area_struct *vma)
@@ -411,6 +411,8 @@ static inline bool anon_vma_name_eq(stru
 		!strcmp(anon_name1->name, anon_name2->name);
 }
 
+struct anon_vma_name *anon_vma_name_get_rcu(struct vm_area_struct *vma);
+
 #else /* CONFIG_ANON_VMA_NAME */
 static inline void anon_vma_name_get(struct anon_vma_name *anon_name) {}
 static inline void anon_vma_name_put(struct anon_vma_name *anon_name) {}
@@ -424,6 +426,12 @@ static inline bool anon_vma_name_eq(stru
 	return true;
 }
 
+static inline
+struct anon_vma_name *anon_vma_name_get_rcu(struct vm_area_struct *vma)
+{
+	return NULL;
+}
+
 #endif  /* CONFIG_ANON_VMA_NAME */
 
 static inline void init_tlb_flush_pending(struct mm_struct *mm)
--- a/include/linux/mm_types.h~mm-make-vm_area_struct-anon_name-field-rcu-safe
+++ a/include/linux/mm_types.h
@@ -545,6 +545,7 @@ struct vm_userfaultfd_ctx {};
 
 struct anon_vma_name {
 	struct kref kref;
+	struct rcu_head rcu;
 	/* The name needs to be at the end because it is dynamically sized. */
 	char name[];
 };
@@ -699,7 +700,7 @@ struct vm_area_struct {
 	 * terminated string containing the name given to the vma, or NULL if
 	 * unnamed. Serialized by mmap_lock. Use anon_vma_name to access.
 	 */
-	struct anon_vma_name *anon_name;
+	struct anon_vma_name __rcu *anon_name;
 #endif
 #ifdef CONFIG_SWAP
 	atomic_long_t swap_readahead_info;
--- a/mm/madvise.c~mm-make-vm_area_struct-anon_name-field-rcu-safe
+++ a/mm/madvise.c
@@ -88,14 +88,15 @@ void anon_vma_name_free(struct kref *kre
 {
 	struct anon_vma_name *anon_name =
 			container_of(kref, struct anon_vma_name, kref);
-	kfree(anon_name);
+	kfree_rcu(anon_name, rcu);
 }
 
 struct anon_vma_name *anon_vma_name(struct vm_area_struct *vma)
 {
 	mmap_assert_locked(vma->vm_mm);
 
-	return vma->anon_name;
+	return rcu_dereference_protected(vma->anon_name,
+		rwsem_is_locked(&vma->vm_mm->mmap_lock));
 }
 
 /* mmap_lock should be write-locked */
@@ -105,7 +106,7 @@ static int replace_anon_vma_name(struct
 	struct anon_vma_name *orig_name = anon_vma_name(vma);
 
 	if (!anon_name) {
-		vma->anon_name = NULL;
+		rcu_assign_pointer(vma->anon_name, NULL);
 		anon_vma_name_put(orig_name);
 		return 0;
 	}
@@ -113,11 +114,32 @@ static int replace_anon_vma_name(struct
 	if (anon_vma_name_eq(orig_name, anon_name))
 		return 0;
 
-	vma->anon_name = anon_vma_name_reuse(anon_name);
+	rcu_assign_pointer(vma->anon_name, anon_vma_name_reuse(anon_name));
 	anon_vma_name_put(orig_name);
 
 	return 0;
 }
+
+/*
+ * Returned anon_vma_name is stable due to elevated refcount but not guaranteed
+ * to be assigned to the original VMA after the call.
+ */
+struct anon_vma_name *anon_vma_name_get_rcu(struct vm_area_struct *vma)
+{
+	struct anon_vma_name __rcu *anon_name;
+
+	WARN_ON_ONCE(!rcu_read_lock_held());
+
+	anon_name = rcu_dereference(vma->anon_name);
+	if (!anon_name)
+		return NULL;
+
+	if (unlikely(!kref_get_unless_zero(&anon_name->kref)))
+		return NULL;
+
+	return anon_name;
+}
+
 #else /* CONFIG_ANON_VMA_NAME */
 static int replace_anon_vma_name(struct vm_area_struct *vma,
 				 struct anon_vma_name *anon_name)
_

Patches currently in -mm which might be from surenb@google.com are

mm-make-vm_area_struct-anon_name-field-rcu-safe.patch
mm-add-mm_struct-sequence-number-to-detect-write-locks.patch
mm-maps-read-proc-pid-maps-under-rcu.patch