Re: [PATCH v4 08/10] mm/vma: improve and document __is_vma_write_locked()

[Vlastimil Babka <vbabka@suse.cz>]

On 1/28/26 12:51, Lorenzo Stoakes wrote:
>>
>> >
>> > Thanks!
>> >
>> > >
>> > > Few nits:
>> > >
>> > > > ---
>> > > >  include/linux/mmap_lock.h | 44 ++++++++++++++++++++++-----------------
>> > > >  1 file changed, 25 insertions(+), 19 deletions(-)
>> > > >
>> > > > diff --git a/include/linux/mmap_lock.h b/include/linux/mmap_lock.h
>> > > > index 678f90080fa6..23bde4bd5a85 100644
>> > > > --- a/include/linux/mmap_lock.h
>> > > > +++ b/include/linux/mmap_lock.h
>> > > > @@ -258,17 +258,30 @@ static inline void vma_end_read(struct vm_area_struct *vma)
>> > > >     vma_refcount_put(vma);
>> > > >  }
>> > > >
>> > > > -/* WARNING! Can only be used if mmap_lock is expected to be write-locked */
>> > > > -static inline bool __is_vma_write_locked(struct vm_area_struct *vma, unsigned int *mm_lock_seq)
>> > > > +static inline unsigned int __vma_raw_mm_seqnum(struct vm_area_struct *vma)
>>
>> This function returns the mm->mm_lock_seq.sequence attribute of mm, so
>> no real commection to VMA. IMO it's better to rename it into
>> __raw_mm_lock_seqnum(const struct mm_struct *mm) and have the callers
>> pass vma->vm_mm.
> 
> Sorry missed these comments.
> 
> We are only ever referencing in terms of VMA's, so I think it makes sense still
> to pass a VMA ptr, even if it just references vma->vm_mm.

FWIW I agree.

> I think the name of the function also makes things pretty clear, given it's
> called essentially 'VMA['s] raw mm seqnum'.
> 
>>
>> > > >  {
>> > > > +   const struct mm_struct *mm = vma->vm_mm;
>> > > > +
>> > > > +   /* We must hold an exclusive write lock for this access to be valid. */
>> > > >     mmap_assert_write_locked(vma->vm_mm);
>>
>> If for some reason you need to keep this function VMA-centric, then in
>> the above line please s/vma->vm_mm/mm
> 
> Ah yeah, maybe if there's a respin? As kinda trivial thing, if that makes sense
> to you!
> 
> Cheers, Lorenzo