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Mon, 18 Nov 2024 13:07:25 +0000 Received: from BYAPR10MB3366.namprd10.prod.outlook.com ([fe80::baf2:dff1:d471:1c9]) by BYAPR10MB3366.namprd10.prod.outlook.com ([fe80::baf2:dff1:d471:1c9%7]) with mapi id 15.20.8158.021; Mon, 18 Nov 2024 13:07:25 +0000 Date: Mon, 18 Nov 2024 13:07:20 +0000 From: Lorenzo Stoakes To: Suren Baghdasaryan Cc: akpm@linux-foundation.org, willy@infradead.org, liam.howlett@oracle.com, mhocko@suse.com, vbabka@suse.cz, hannes@cmpxchg.org, mjguzik@gmail.com, oliver.sang@intel.com, mgorman@techsingularity.net, david@redhat.com, peterx@redhat.com, oleg@redhat.com, dave@stgolabs.net, paulmck@kernel.org, brauner@kernel.org, dhowells@redhat.com, hdanton@sina.com, hughd@google.com, minchan@google.com, jannh@google.com, shakeel.butt@linux.dev, souravpanda@google.com, pasha.tatashin@soleen.com, corbet@lwn.net, linux-doc@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@android.com Subject: Re: [PATCH v3 1/5] mm: introduce vma_start_read_locked{_nested} helpers Message-ID: <12322f85-44fd-4b03-ae9d-81d42b977d32@lucifer.local> References: <20241117080931.600731-1-surenb@google.com> <20241117080931.600731-2-surenb@google.com> Content-Type: text/plain; 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Replace direct accesses to vma->vm_lock > with these new helpers. > > Signed-off-by: Suren Baghdasaryan LGTM thanks: Reviewed-by: Lorenzo Stoakes > --- > include/linux/mm.h | 24 ++++++++++++++++++++++++ > mm/userfaultfd.c | 22 +++++----------------- > 2 files changed, 29 insertions(+), 17 deletions(-) > > diff --git a/include/linux/mm.h b/include/linux/mm.h > index fecd47239fa9..1ba2e480ae63 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -722,6 +722,30 @@ static inline bool vma_start_read(struct vm_area_struct *vma) > return true; > } > > +/* > + * Use only while holding mmap read lock which guarantees that locking will not > + * fail (nobody can concurrently write-lock the vma). vma_start_read() should > + * not be used in such cases because it might fail due to mm_lock_seq overflow. > + * This functionality is used to obtain vma read lock and drop the mmap read lock. > + */ > +static inline void vma_start_read_locked_nested(struct vm_area_struct *vma, int subclass) > +{ > + mmap_assert_locked(vma->vm_mm); > + down_read_nested(&vma->vm_lock->lock, subclass); > +} > + > +/* > + * Use only while holding mmap read lock which guarantees that locking will not > + * fail (nobody can concurrently write-lock the vma). vma_start_read() should > + * not be used in such cases because it might fail due to mm_lock_seq overflow. > + * This functionality is used to obtain vma read lock and drop the mmap read lock. > + */ > +static inline void vma_start_read_locked(struct vm_area_struct *vma) > +{ > + mmap_assert_locked(vma->vm_mm); > + down_read(&vma->vm_lock->lock); > +} > + > static inline void vma_end_read(struct vm_area_struct *vma) > { > rcu_read_lock(); /* keeps vma alive till the end of up_read */ > diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c > index 60a0be33766f..87db4b32b82a 100644 > --- a/mm/userfaultfd.c > +++ b/mm/userfaultfd.c > @@ -84,16 +84,8 @@ static struct vm_area_struct *uffd_lock_vma(struct mm_struct *mm, > > mmap_read_lock(mm); > vma = find_vma_and_prepare_anon(mm, address); > - if (!IS_ERR(vma)) { > - /* > - * We cannot use vma_start_read() as it may fail due to > - * false locked (see comment in vma_start_read()). We > - * can avoid that by directly locking vm_lock under > - * mmap_lock, which guarantees that nobody can lock the > - * vma for write (vma_start_write()) under us. > - */ > - down_read(&vma->vm_lock->lock); > - } > + if (!IS_ERR(vma)) > + vma_start_read_locked(vma); > > mmap_read_unlock(mm); > return vma; > @@ -1476,14 +1468,10 @@ static int uffd_move_lock(struct mm_struct *mm, > mmap_read_lock(mm); > err = find_vmas_mm_locked(mm, dst_start, src_start, dst_vmap, src_vmap); > if (!err) { > - /* > - * See comment in uffd_lock_vma() as to why not using > - * vma_start_read() here. > - */ > - down_read(&(*dst_vmap)->vm_lock->lock); > + vma_start_read_locked(*dst_vmap); > if (*dst_vmap != *src_vmap) > - down_read_nested(&(*src_vmap)->vm_lock->lock, > - SINGLE_DEPTH_NESTING); > + vma_start_read_locked_nested(*src_vmap, > + SINGLE_DEPTH_NESTING); > } > mmap_read_unlock(mm); > return err; > -- > 2.47.0.338.g60cca15819-goog >