Re: [PATCH] mm: lock newly mapped VMA with corrected ordering

[Suren Baghdasaryan]

On Sat, Jul 8, 2023 at 4:10 PM Suren Baghdasaryan  wrote:
>
> On Sat, Jul 8, 2023 at 4:04 PM Hugh Dickins  wrote:
> >
> > Lockdep is certainly right to complain about
> > (>vm_lock->lock){}-{3:3}, at: vma_start_write+0x2d/0x3f
> >but task is already holding lock:
> > (>i_mmap_rwsem){+.+.}-{3:3}, at: mmap_region+0x4dc/0x6db
> > Invert those to the usual ordering.
>
> Doh! Thanks Hugh!
> I totally forgot to run this with lockdep enabled :(

I verified both the lockdep warning and the fix. Thanks again, Hugh!

Tested-by: Suren Baghdasaryan 

>
> >
> > Fixes: 33313a747e81 ("mm: lock newly mapped VMA which can be modified after 
> > it becomes visible")
> > Cc: sta...@vger.kernel.org
> > Signed-off-by: Hugh Dickins 
> > ---
> >  mm/mmap.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/mm/mmap.c b/mm/mmap.c
> > index 84c71431a527..3eda23c9ebe7 100644
> > --- a/mm/mmap.c
> > +++ b/mm/mmap.c
> > @@ -2809,11 +2809,11 @@ unsigned long mmap_region(struct file *file, 
> > unsigned long addr,
> > if (vma_iter_prealloc())
> > goto close_and_free_vma;
> >
> > +   /* Lock the VMA since it is modified after insertion into VMA tree 
> > */
> > +   vma_start_write(vma);
> > if (vma->vm_file)
> > i_mmap_lock_write(vma->vm_file->f_mapping);
> >
> > -   /* Lock the VMA since it is modified after insertion into VMA tree 
> > */
> > -   vma_start_write(vma);
> > vma_iter_store(, vma);
> > mm->map_count++;
> > if (vma->vm_file) {
> > --
> > 2.35.3

Re: [PATCH] mm: lock newly mapped VMA with corrected ordering

[Suren Baghdasaryan]

On Sat, Jul 8, 2023 at 4:04 PM Hugh Dickins  wrote:
>
> Lockdep is certainly right to complain about
> (>vm_lock->lock){}-{3:3}, at: vma_start_write+0x2d/0x3f
>but task is already holding lock:
> (>i_mmap_rwsem){+.+.}-{3:3}, at: mmap_region+0x4dc/0x6db
> Invert those to the usual ordering.

Doh! Thanks Hugh!
I totally forgot to run this with lockdep enabled :(

>
> Fixes: 33313a747e81 ("mm: lock newly mapped VMA which can be modified after 
> it becomes visible")
> Cc: sta...@vger.kernel.org
> Signed-off-by: Hugh Dickins 
> ---
>  mm/mmap.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/mm/mmap.c b/mm/mmap.c
> index 84c71431a527..3eda23c9ebe7 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -2809,11 +2809,11 @@ unsigned long mmap_region(struct file *file, unsigned 
> long addr,
> if (vma_iter_prealloc())
> goto close_and_free_vma;
>
> +   /* Lock the VMA since it is modified after insertion into VMA tree */
> +   vma_start_write(vma);
> if (vma->vm_file)
> i_mmap_lock_write(vma->vm_file->f_mapping);
>
> -   /* Lock the VMA since it is modified after insertion into VMA tree */
> -   vma_start_write(vma);
> vma_iter_store(, vma);
> mm->map_count++;
> if (vma->vm_file) {
> --
> 2.35.3

[PATCH] mm: lock newly mapped VMA with corrected ordering

[Hugh Dickins]

Lockdep is certainly right to complain about
(>vm_lock->lock){}-{3:3}, at: vma_start_write+0x2d/0x3f
   but task is already holding lock:
(>i_mmap_rwsem){+.+.}-{3:3}, at: mmap_region+0x4dc/0x6db
Invert those to the usual ordering.

Fixes: 33313a747e81 ("mm: lock newly mapped VMA which can be modified after it 
becomes visible")
Cc: sta...@vger.kernel.org
Signed-off-by: Hugh Dickins 
---
 mm/mmap.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/mmap.c b/mm/mmap.c
index 84c71431a527..3eda23c9ebe7 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2809,11 +2809,11 @@ unsigned long mmap_region(struct file *file, unsigned 
long addr,
if (vma_iter_prealloc())
goto close_and_free_vma;
 
+   /* Lock the VMA since it is modified after insertion into VMA tree */
+   vma_start_write(vma);
if (vma->vm_file)
i_mmap_lock_write(vma->vm_file->f_mapping);
 
-   /* Lock the VMA since it is modified after insertion into VMA tree */
-   vma_start_write(vma);
vma_iter_store(, vma);
mm->map_count++;
if (vma->vm_file) {
-- 
2.35.3