lisa/android_kernel_xiaomi_sm8350
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Revert "mm/rmap: Fix anon_vma->degree ambiguity leading to double-reuse"

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This reverts commit 2fe3eee488 which is
commit 2555283eb40df89945557273121e9393ef9b542b upstream.

It currently breaks the Android kernel ABI.  If it needs to come back,
it should be done in an ABI-safe way.

Bug: 161946584
Cc: Jann Horn <jannh@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
Change-Id: I46a7a4ffc5d2725146787ea7273a42a5cf062ed4
This commit is contained in:
Greg Kroah-Hartman 2022-09-21 11:10:07 +02:00
parent 51223c9db5
commit d52832d985
2 changed files with 16 additions and 22 deletions
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7
include/linux/rmap.h
View File

@ -39,15 +39,12 @@ struct anon_vma {
atomic_t refcount;
/*
* Count of child anon_vmas. Equals to the count of all anon_vmas that
* have ->parent pointing to this one, including itself.
* 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 long num_children;
/* Count of VMAs whose ->anon_vma pointer points to this object. */
unsigned long num_active_vmas;
unsigned degree;
struct anon_vma *parent; /* Parent of this anon_vma */

31
mm/rmap.c
View File

@ -83,8 +83,7 @@ static inline struct anon_vma *anon_vma_alloc(void)
anon_vma = kmem_cache_alloc(anon_vma_cachep, GFP_KERNEL);
if (anon_vma) {
atomic_set(&anon_vma->refcount, 1);
anon_vma->num_children = 0;
anon_vma->num_active_vmas = 0;
anon_vma->degree = 1; /* Reference for first vma */
anon_vma->parent = anon_vma;
/*
* Initialise the anon_vma root to point to itself. If called
@ -192,7 +191,6 @@ int __anon_vma_prepare(struct vm_area_struct *vma)
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;
}
@ -202,7 +200,8 @@ int __anon_vma_prepare(struct vm_area_struct *vma)
if (likely(!vma->anon_vma)) {
vma->anon_vma = anon_vma;
anon_vma_chain_link(vma, avc, anon_vma);
anon_vma->num_active_vmas++;
/* vma reference or self-parent link for new root */
anon_vma->degree++;
allocated = NULL;
avc = NULL;
}
@ -281,19 +280,19 @@ int anon_vma_clone(struct vm_area_struct *dst, struct vm_area_struct *src)
anon_vma_chain_link(dst, avc, anon_vma);
/*
* Reuse existing anon_vma if it has no vma and only one
* anon_vma child.
* Reuse existing anon_vma if its degree lower than two,
* that means it has no vma and only one anon_vma child.
*
* Root anon_vma is never reused:
* Do not chose parent anon_vma, otherwise first child
* will always reuse it. Root anon_vma is never reused:
* it has self-parent reference and at least one child.
*/
if (!dst->anon_vma &&
anon_vma->num_children < 2 &&
anon_vma->num_active_vmas == 0)
if (!dst->anon_vma && anon_vma != src->anon_vma &&
anon_vma->degree < 2)
dst->anon_vma = anon_vma;
}
if (dst->anon_vma)
dst->anon_vma->num_active_vmas++;
dst->anon_vma->degree++;
unlock_anon_vma_root(root);
return 0;
@ -343,7 +342,6 @@ int anon_vma_fork(struct vm_area_struct *vma, struct vm_area_struct *pvma)
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;
@ -364,7 +362,7 @@ int anon_vma_fork(struct vm_area_struct *vma, struct vm_area_struct *pvma)
vma->anon_vma = anon_vma;
anon_vma_lock_write(anon_vma);
anon_vma_chain_link(vma, avc, anon_vma);
anon_vma->parent->num_children++;
anon_vma->parent->degree++;
anon_vma_unlock_write(anon_vma);
return 0;
@ -396,7 +394,7 @@ void unlink_anon_vmas(struct vm_area_struct *vma)
* to free them outside the lock.
*/
if (RB_EMPTY_ROOT(&anon_vma->rb_root.rb_root)) {
anon_vma->parent->num_children--;
anon_vma->parent->degree--;
continue;
}
@ -404,7 +402,7 @@ void unlink_anon_vmas(struct vm_area_struct *vma)
anon_vma_chain_free(avc);
}
if (vma->anon_vma)
vma->anon_vma->num_active_vmas--;
vma->anon_vma->degree--;
unlock_anon_vma_root(root);
/*
@ -415,8 +413,7 @@ void unlink_anon_vmas(struct vm_area_struct *vma)
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->num_children);
VM_WARN_ON(anon_vma->num_active_vmas);
VM_WARN_ON(anon_vma->degree);
put_anon_vma(anon_vma);
list_del(&avc->same_vma);