diff mbox series

[v4,24/33] mm: fall back to mmap_lock if vma->anon_vma is not yet set

Message ID 20230227173632.3292573-25-surenb@google.com (mailing list archive)
State New
Headers show
Series Per-VMA locks | expand

Commit Message

Suren Baghdasaryan Feb. 27, 2023, 5:36 p.m. UTC 
When vma->anon_vma is not set, page fault handler will set it by either
reusing anon_vma of an adjacent VMA if VMAs are compatible or by
allocating a new one. find_mergeable_anon_vma() walks VMA tree to find
a compatible adjacent VMA and that requires not only the faulting VMA
to be stable but also the tree structure and other VMAs inside that tree.
Therefore locking just the faulting VMA is not enough for this search.
Fall back to taking mmap_lock when vma->anon_vma is not set. This
situation happens only on the first page fault and should not affect
overall performance.

Signed-off-by: Suren Baghdasaryan <surenb@google.com>
---
 mm/memory.c | 4 ++++
 1 file changed, 4 insertions(+)

Comments

Hyeonggon Yoo March 1, 2023, 9:54 a.m. UTC | #1 
On Mon, Feb 27, 2023 at 09:36:23AM -0800, Suren Baghdasaryan wrote:
> When vma->anon_vma is not set, page fault handler will set it by either
> reusing anon_vma of an adjacent VMA if VMAs are compatible or by
> allocating a new one. find_mergeable_anon_vma() walks VMA tree to find
> a compatible adjacent VMA and that requires not only the faulting VMA
> to be stable but also the tree structure and other VMAs inside that tree.
> Therefore locking just the faulting VMA is not enough for this search.
> Fall back to taking mmap_lock when vma->anon_vma is not set. This
> situation happens only on the first page fault and should not affect
> overall performance.
> 
> Signed-off-by: Suren Baghdasaryan <surenb@google.com>
> ---
>  mm/memory.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/mm/memory.c b/mm/memory.c
> index bda4c1a991f0..8855846a361b 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -5243,6 +5243,10 @@ struct vm_area_struct *lock_vma_under_rcu(struct mm_struct *mm,
>  	if (!vma_is_anonymous(vma))
>  		goto inval;
>  
> +	/* find_mergeable_anon_vma uses adjacent vmas which are not locked */
> +	if (!vma->anon_vma)
> +		goto inval;
> +
>  	if (!vma_start_read(vma))
>  		goto inval;

Reviewed-by: Hyeonggon Yoo <42.hyeyoo@gmail.com>

> -- 
> 2.39.2.722.g9855ee24e9-goog
> 
>
diff mbox series

Patch

diff --git a/mm/memory.c b/mm/memory.c
index bda4c1a991f0..8855846a361b 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -5243,6 +5243,10 @@  struct vm_area_struct *lock_vma_under_rcu(struct mm_struct *mm,
 	if (!vma_is_anonymous(vma))
 		goto inval;
 
+	/* find_mergeable_anon_vma uses adjacent vmas which are not locked */
+	if (!vma->anon_vma)
+		goto inval;
+
 	if (!vma_start_read(vma))
 		goto inval;