* Suren Baghdasaryan <surenb@xxxxxxxxxx> [210528 20:42]:
> On Wed, Apr 28, 2021 at 8:36 AM Liam Howlett <liam.howlett@xxxxxxxxxx> wrote:
> >
> > Use the maple tree iterator to duplicate the mm_struct trees.
> >
> > Signed-off-by: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx>
> > ---
> > include/linux/mm.h | 2 --
> > include/linux/sched/mm.h | 3 +++
> > kernel/fork.c | 24 +++++++++++++++++++-----
> > mm/mmap.c | 4 ----
> > 4 files changed, 22 insertions(+), 11 deletions(-)
> >
> > diff --git a/include/linux/mm.h b/include/linux/mm.h
> > index e89bacfa9145..7f7dff6ad884 100644
> > --- a/include/linux/mm.h
> > +++ b/include/linux/mm.h
> > @@ -2498,8 +2498,6 @@ extern bool arch_has_descending_max_zone_pfns(void);
> > /* nommu.c */
> > extern atomic_long_t mmap_pages_allocated;
> > extern int nommu_shrink_inode_mappings(struct inode *, size_t, size_t);
> > -/* maple_tree */
> > -void vma_store(struct mm_struct *mm, struct vm_area_struct *vma);
> >
> > /* interval_tree.c */
> > void vma_interval_tree_insert(struct vm_area_struct *node,
> > diff --git a/include/linux/sched/mm.h b/include/linux/sched/mm.h
> > index e24b1fe348e3..76cab3aea6ab 100644
> > --- a/include/linux/sched/mm.h
> > +++ b/include/linux/sched/mm.h
> > @@ -8,6 +8,7 @@
> > #include <linux/mm_types.h>
> > #include <linux/gfp.h>
> > #include <linux/sync_core.h>
> > +#include <linux/maple_tree.h>
> >
> > /*
> > * Routines for handling mm_structs
> > @@ -67,11 +68,13 @@ static inline void mmdrop(struct mm_struct *mm)
> > */
> > static inline void mmget(struct mm_struct *mm)
> > {
> > + mt_set_in_rcu(&mm->mm_mt);
> > atomic_inc(&mm->mm_users);
> > }
> >
> > static inline bool mmget_not_zero(struct mm_struct *mm)
> > {
> > + mt_set_in_rcu(&mm->mm_mt);
>
> Should you be calling mt_set_in_rcu() if atomic_inc_not_zero() failed?
> I don't think mmput() is called after mmget_not_zero() fails and
> mt_clear_in_rcu() will not be called.
Good catch, but having it the way it is will be faster with the
possibility of re-entering RCU mode if there is a race during tear down.
Entering RCU mode during tear-down mean that the nodes that are not
already freed would remain for an RCU cycle before being freed. I don't
think it is worth checking every time this is called for such a low
payoff. I should probably add a comment about this though.
>
> > return atomic_inc_not_zero(&mm->mm_users);
> > }
> >
> > diff --git a/kernel/fork.c b/kernel/fork.c
> > index c37abaf28eb9..832416ff613e 100644
> > --- a/kernel/fork.c
> > +++ b/kernel/fork.c
> > @@ -477,7 +477,9 @@ static __latent_entropy int dup_mmap(struct mm_struct *mm,
> > struct vm_area_struct *mpnt, *tmp, *prev, **pprev;
> > struct rb_node **rb_link, *rb_parent;
> > int retval;
> > - unsigned long charge;
> > + unsigned long charge = 0;
> > + MA_STATE(old_mas, &oldmm->mm_mt, 0, 0);
> > + MA_STATE(mas, &mm->mm_mt, 0, 0);
> > LIST_HEAD(uf);
> >
> > uprobe_start_dup_mmap();
> > @@ -511,7 +513,13 @@ static __latent_entropy int dup_mmap(struct mm_struct *mm,
> > goto out;
> >
> > prev = NULL;
> > - for (mpnt = oldmm->mmap; mpnt; mpnt = mpnt->vm_next) {
> > +
> > + retval = mas_entry_count(&mas, oldmm->map_count);
> > + if (retval)
> > + goto fail_nomem;
> > +
> > + rcu_read_lock();
> > + mas_for_each(&old_mas, mpnt, ULONG_MAX) {
> > struct file *file;
> >
> > if (mpnt->vm_flags & VM_DONTCOPY) {
> > @@ -525,7 +533,7 @@ static __latent_entropy int dup_mmap(struct mm_struct *mm,
> > */
> > if (fatal_signal_pending(current)) {
> > retval = -EINTR;
> > - goto out;
> > + goto loop_out;
> > }
> > if (mpnt->vm_flags & VM_ACCOUNT) {
> > unsigned long len = vma_pages(mpnt);
> > @@ -594,7 +602,9 @@ static __latent_entropy int dup_mmap(struct mm_struct *mm,
> > rb_parent = &tmp->vm_rb;
> >
> > /* Link the vma into the MT */
> > - vma_store(mm, tmp);
> > + mas.index = tmp->vm_start;
> > + mas.last = tmp->vm_end - 1;
> > + mas_store(&mas, tmp);
> >
> > mm->map_count++;
> > if (!(tmp->vm_flags & VM_WIPEONFORK))
> > @@ -604,14 +614,17 @@ static __latent_entropy int dup_mmap(struct mm_struct *mm,
> > tmp->vm_ops->open(tmp);
> >
> > if (retval)
> > - goto out;
> > + goto loop_out;
> > }
> > /* a new mm has just been created */
> > retval = arch_dup_mmap(oldmm, mm);
> > +loop_out:
> > out:
> > + rcu_read_unlock();
> > mmap_write_unlock(mm);
> > flush_tlb_mm(oldmm);
> > mmap_write_unlock(oldmm);
> > + mas_destroy(&mas);
> > dup_userfaultfd_complete(&uf);
> > fail_uprobe_end:
> > uprobe_end_dup_mmap();
> > @@ -1092,6 +1105,7 @@ static inline void __mmput(struct mm_struct *mm)
> > {
> > VM_BUG_ON(atomic_read(&mm->mm_users));
> >
> > + mt_clear_in_rcu(&mm->mm_mt);
> > uprobe_clear_state(mm);
> > exit_aio(mm);
> > ksm_exit(mm);
> > diff --git a/mm/mmap.c b/mm/mmap.c
> > index 929c2f9eb3f5..1bd43f4db28e 100644
> > --- a/mm/mmap.c
> > +++ b/mm/mmap.c
> > @@ -780,10 +780,6 @@ static inline void vma_mt_store(struct mm_struct *mm, struct vm_area_struct *vma
> > GFP_KERNEL);
> > }
> >
> > -void vma_store(struct mm_struct *mm, struct vm_area_struct *vma) {
> > - vma_mt_store(mm, vma);
> > -}
> > -
> > static void
> > __vma_link(struct mm_struct *mm, struct vm_area_struct *vma,
> > struct vm_area_struct *prev, struct rb_node **rb_link,
> > --
> > 2.30.2
