Revert "Revert "mm/rmap: Fix anon_vma->degree ambiguity leading to double-reuse""
This reverts commit 4f35cec76058557d9eaec0d501d03c7657eb56b4 and does so
in an abi-safe way.
This is done by adding the new fields only to the end of the structure
and this structure is only passed around to other functions as a
pointer, the internal structure layout is only touched by the core
kernel, so adding it to the end is safe.
Bug: 260678056
Bug: 253167854
Change-Id: Ib1d45625cbc2e0b21330ca3dc2aa7aff34666d31
Signed-off-by: Lee Jones <joneslee@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
(cherry picked from commit 4158b1508f2b120db810607ce2c1fd6d948c8740)
diff --git a/android/abi_gki_aarch64.xml b/android/abi_gki_aarch64.xml
index 94ed4f9..3aa56cc 100644
--- a/android/abi_gki_aarch64.xml
+++ b/android/abi_gki_aarch64.xml
@@ -15379,7 +15379,7 @@
<return type-id='48b5725f'/>
</function-type>
<pointer-type-def type-id='2b7b3388' size-in-bits='64' id='14f24806'/>
- <class-decl name='anon_vma' size-in-bits='832' is-struct='yes' visibility='default' filepath='include/linux/rmap.h' line='33' column='1' id='14f332cc'>
+ <class-decl name='anon_vma' size-in-bits='960' is-struct='yes' visibility='default' filepath='include/linux/rmap.h' line='33' column='1' id='14f332cc'>
<data-member access='public' layout-offset-in-bits='0'>
<var-decl name='root' type-id='a8f86cda' visibility='default' filepath='include/linux/rmap.h' line='34' column='1'/>
</data-member>
@@ -15390,13 +15390,19 @@
<var-decl name='refcount' type-id='49178f86' visibility='default' filepath='include/linux/rmap.h' line='43' column='1'/>
</data-member>
<data-member access='public' layout-offset-in-bits='608'>
- <var-decl name='degree' type-id='f0981eeb' visibility='default' filepath='include/linux/rmap.h' line='51' column='1'/>
+ <var-decl name='degree' type-id='f0981eeb' visibility='default' filepath='include/linux/rmap.h' line='45' column='1'/>
</data-member>
<data-member access='public' layout-offset-in-bits='640'>
- <var-decl name='parent' type-id='a8f86cda' visibility='default' filepath='include/linux/rmap.h' line='53' column='1'/>
+ <var-decl name='parent' type-id='a8f86cda' visibility='default' filepath='include/linux/rmap.h' line='47' column='1'/>
</data-member>
<data-member access='public' layout-offset-in-bits='704'>
- <var-decl name='rb_root' type-id='6fe1603d' visibility='default' filepath='include/linux/rmap.h' line='65' column='1'/>
+ <var-decl name='rb_root' type-id='6fe1603d' visibility='default' filepath='include/linux/rmap.h' line='59' column='1'/>
+ </data-member>
+ <data-member access='public' layout-offset-in-bits='832'>
+ <var-decl name='num_children' type-id='7359adad' visibility='default' filepath='include/linux/rmap.h' line='74' column='1'/>
+ </data-member>
+ <data-member access='public' layout-offset-in-bits='896'>
+ <var-decl name='num_active_vmas' type-id='7359adad' visibility='default' filepath='include/linux/rmap.h' line='76' column='1'/>
</data-member>
</class-decl>
<pointer-type-def type-id='031a4ff0' size-in-bits='64' id='1507ee2a'/>
@@ -161594,7 +161600,6 @@
</abi-instr>
</abi-corpus>
</abi-corpus-group>
-
<!--
libabigail: abidw: 2.1.0SOONG BUILD NUMBER PLACEHOLDER
-->
diff --git a/include/linux/rmap.h b/include/linux/rmap.h
index 47a5388..b44dd56 100644
--- a/include/linux/rmap.h
+++ b/include/linux/rmap.h
@@ -42,13 +42,7 @@
*/
atomic_t refcount;
- /*
- * Count of child anon_vmas and VMAs which points to this anon_vma.
- *
- * This counter is used for making decision about reusing anon_vma
- * instead of forking new one. See comments in function anon_vma_clone.
- */
- unsigned degree;
+ unsigned degree; /* ANDROID: KABI preservation, DO NOT USE! */
struct anon_vma *parent; /* Parent of this anon_vma */
@@ -63,6 +57,25 @@
/* Interval tree of private "related" vmas */
struct rb_root_cached rb_root;
+
+ /*
+ * ANDROID: KABI preservation, it's safe to put these at the end of this structure as it's
+ * only passed by a pointer everywhere, the size and internal structures are local to the
+ * core kernel.
+ */
+#ifndef __GENKSYMS__
+ /*
+ * Count of child anon_vmas. Equals to the count of all anon_vmas that
+ * have ->parent pointing to this one, including itself.
+ *
+ * This counter is used for making decision about reusing anon_vma
+ * instead of forking new one. See comments in function anon_vma_clone.
+ */
+ unsigned long num_children;
+ /* Count of VMAs whose ->anon_vma pointer points to this object. */
+ unsigned long num_active_vmas;
+#endif
+
};
/*
diff --git a/mm/rmap.c b/mm/rmap.c
index e655282..9bbe9f1 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -93,7 +93,8 @@
anon_vma = kmem_cache_alloc(anon_vma_cachep, GFP_KERNEL);
if (anon_vma) {
atomic_set(&anon_vma->refcount, 1);
- anon_vma->degree = 1; /* Reference for first vma */
+ anon_vma->num_children = 0;
+ anon_vma->num_active_vmas = 0;
anon_vma->parent = anon_vma;
/*
* Initialise the anon_vma root to point to itself. If called
@@ -201,6 +202,7 @@
anon_vma = anon_vma_alloc();
if (unlikely(!anon_vma))
goto out_enomem_free_avc;
+ anon_vma->num_children++; /* self-parent link for new root */
allocated = anon_vma;
}
@@ -210,8 +212,7 @@
if (likely(!vma->anon_vma)) {
vma->anon_vma = anon_vma;
anon_vma_chain_link(vma, avc, anon_vma);
- /* vma reference or self-parent link for new root */
- anon_vma->degree++;
+ anon_vma->num_active_vmas++;
allocated = NULL;
avc = NULL;
}
@@ -296,19 +297,19 @@
anon_vma_chain_link(dst, avc, anon_vma);
/*
- * Reuse existing anon_vma if its degree lower than two,
- * that means it has no vma and only one anon_vma child.
+ * Reuse existing anon_vma if it has no vma and only one
+ * anon_vma child.
*
- * Do not chose parent anon_vma, otherwise first child
- * will always reuse it. Root anon_vma is never reused:
+ * Root anon_vma is never reused:
* it has self-parent reference and at least one child.
*/
if (!dst->anon_vma && src->anon_vma &&
- anon_vma != src->anon_vma && anon_vma->degree < 2)
+ anon_vma->num_children < 2 &&
+ anon_vma->num_active_vmas == 0)
dst->anon_vma = anon_vma;
}
if (dst->anon_vma)
- dst->anon_vma->degree++;
+ dst->anon_vma->num_active_vmas++;
unlock_anon_vma_root(root);
return 0;
@@ -358,6 +359,7 @@
anon_vma = anon_vma_alloc();
if (!anon_vma)
goto out_error;
+ anon_vma->num_active_vmas++;
avc = anon_vma_chain_alloc(GFP_KERNEL);
if (!avc)
goto out_error_free_anon_vma;
@@ -378,7 +380,7 @@
vma->anon_vma = anon_vma;
anon_vma_lock_write(anon_vma);
anon_vma_chain_link(vma, avc, anon_vma);
- anon_vma->parent->degree++;
+ anon_vma->parent->num_children++;
anon_vma_unlock_write(anon_vma);
return 0;
@@ -410,7 +412,7 @@
* to free them outside the lock.
*/
if (RB_EMPTY_ROOT(&anon_vma->rb_root.rb_root)) {
- anon_vma->parent->degree--;
+ anon_vma->parent->num_children--;
continue;
}
@@ -418,7 +420,7 @@
anon_vma_chain_free(avc);
}
if (vma->anon_vma) {
- vma->anon_vma->degree--;
+ vma->anon_vma->num_active_vmas--;
#ifndef CONFIG_SPECULATIVE_PAGE_FAULT
/*
@@ -438,7 +440,8 @@
list_for_each_entry_safe(avc, next, &vma->anon_vma_chain, same_vma) {
struct anon_vma *anon_vma = avc->anon_vma;
- VM_WARN_ON(anon_vma->degree);
+ VM_WARN_ON(anon_vma->num_children);
+ VM_WARN_ON(anon_vma->num_active_vmas);
put_anon_vma(anon_vma);
list_del(&avc->same_vma);
