On Tue, Apr 16, 2019 at 03:45:10PM +0200, Laurent Dufour wrote: > Introducing a per mm_struct seqlock, mm_seq field, to protect the changes > made in the MM RB tree. This allows to walk the RB tree without grabbing > the mmap_sem, and on the walk is done to double check that sequence counter > was stable during the walk. > > The mm seqlock is held while inserting and removing entries into the MM RB > tree. Later in this series, it will be check when looking for a VMA > without holding the mmap_sem. > > This is based on the initial work from Peter Zijlstra: > https://lore.kernel.org/linux-mm/20100104182813.479668508@xxxxxxxxx/ > > Signed-off-by: Laurent Dufour <ldufour@xxxxxxxxxxxxx> Reviewed-by: Jérôme Glisse <jglisse@xxxxxxxxxx> > --- > include/linux/mm_types.h | 3 +++ > kernel/fork.c | 3 +++ > mm/init-mm.c | 3 +++ > mm/mmap.c | 48 +++++++++++++++++++++++++++++++--------- > 4 files changed, 46 insertions(+), 11 deletions(-) > > diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h > index e78f72eb2576..24b3f8ce9e42 100644 > --- a/include/linux/mm_types.h > +++ b/include/linux/mm_types.h > @@ -358,6 +358,9 @@ struct mm_struct { > struct { > struct vm_area_struct *mmap; /* list of VMAs */ > struct rb_root mm_rb; > +#ifdef CONFIG_SPECULATIVE_PAGE_FAULT > + seqlock_t mm_seq; > +#endif > u64 vmacache_seqnum; /* per-thread vmacache */ > #ifdef CONFIG_MMU > unsigned long (*get_unmapped_area) (struct file *filp, > diff --git a/kernel/fork.c b/kernel/fork.c > index 2992d2c95256..3a1739197ebc 100644 > --- a/kernel/fork.c > +++ b/kernel/fork.c > @@ -1008,6 +1008,9 @@ static struct mm_struct *mm_init(struct mm_struct *mm, struct task_struct *p, > mm->mmap = NULL; > mm->mm_rb = RB_ROOT; > mm->vmacache_seqnum = 0; > +#ifdef CONFIG_SPECULATIVE_PAGE_FAULT > + seqlock_init(&mm->mm_seq); > +#endif > atomic_set(&mm->mm_users, 1); > atomic_set(&mm->mm_count, 1); > init_rwsem(&mm->mmap_sem); > diff --git a/mm/init-mm.c b/mm/init-mm.c > index a787a319211e..69346b883a4e 100644 > --- a/mm/init-mm.c > +++ b/mm/init-mm.c > @@ -27,6 +27,9 @@ > */ > struct mm_struct init_mm = { > .mm_rb = RB_ROOT, > +#ifdef CONFIG_SPECULATIVE_PAGE_FAULT > + .mm_seq = __SEQLOCK_UNLOCKED(init_mm.mm_seq), > +#endif > .pgd = swapper_pg_dir, > .mm_users = ATOMIC_INIT(2), > .mm_count = ATOMIC_INIT(1), > diff --git a/mm/mmap.c b/mm/mmap.c > index 13460b38b0fb..f7f6027a7dff 100644 > --- a/mm/mmap.c > +++ b/mm/mmap.c > @@ -170,6 +170,24 @@ void unlink_file_vma(struct vm_area_struct *vma) > } > } > > +#ifdef CONFIG_SPECULATIVE_PAGE_FAULT > +static inline void mm_write_seqlock(struct mm_struct *mm) > +{ > + write_seqlock(&mm->mm_seq); > +} > +static inline void mm_write_sequnlock(struct mm_struct *mm) > +{ > + write_sequnlock(&mm->mm_seq); > +} > +#else > +static inline void mm_write_seqlock(struct mm_struct *mm) > +{ > +} > +static inline void mm_write_sequnlock(struct mm_struct *mm) > +{ > +} > +#endif /* CONFIG_SPECULATIVE_PAGE_FAULT */ > + > /* > * Close a vm structure and free it, returning the next. > */ > @@ -445,26 +463,32 @@ static void vma_gap_update(struct vm_area_struct *vma) > } > > static inline void vma_rb_insert(struct vm_area_struct *vma, > - struct rb_root *root) > + struct mm_struct *mm) > { > + struct rb_root *root = &mm->mm_rb; > + > /* All rb_subtree_gap values must be consistent prior to insertion */ > validate_mm_rb(root, NULL); > > rb_insert_augmented(&vma->vm_rb, root, &vma_gap_callbacks); > } > > -static void __vma_rb_erase(struct vm_area_struct *vma, struct rb_root *root) > +static void __vma_rb_erase(struct vm_area_struct *vma, struct mm_struct *mm) > { > + struct rb_root *root = &mm->mm_rb; > + > /* > * Note rb_erase_augmented is a fairly large inline function, > * so make sure we instantiate it only once with our desired > * augmented rbtree callbacks. > */ > + mm_write_seqlock(mm); > rb_erase_augmented(&vma->vm_rb, root, &vma_gap_callbacks); > + mm_write_sequnlock(mm); /* wmb */ > } > > static __always_inline void vma_rb_erase_ignore(struct vm_area_struct *vma, > - struct rb_root *root, > + struct mm_struct *mm, > struct vm_area_struct *ignore) > { > /* > @@ -472,21 +496,21 @@ static __always_inline void vma_rb_erase_ignore(struct vm_area_struct *vma, > * with the possible exception of the "next" vma being erased if > * next->vm_start was reduced. > */ > - validate_mm_rb(root, ignore); > + validate_mm_rb(&mm->mm_rb, ignore); > > - __vma_rb_erase(vma, root); > + __vma_rb_erase(vma, mm); > } > > static __always_inline void vma_rb_erase(struct vm_area_struct *vma, > - struct rb_root *root) > + struct mm_struct *mm) > { > /* > * All rb_subtree_gap values must be consistent prior to erase, > * with the possible exception of the vma being erased. > */ > - validate_mm_rb(root, vma); > + validate_mm_rb(&mm->mm_rb, vma); > > - __vma_rb_erase(vma, root); > + __vma_rb_erase(vma, mm); > } > > /* > @@ -601,10 +625,12 @@ void __vma_link_rb(struct mm_struct *mm, struct vm_area_struct *vma, > * immediately update the gap to the correct value. Finally we > * rebalance the rbtree after all augmented values have been set. > */ > + mm_write_seqlock(mm); > rb_link_node(&vma->vm_rb, rb_parent, rb_link); > vma->rb_subtree_gap = 0; > vma_gap_update(vma); > - vma_rb_insert(vma, &mm->mm_rb); > + vma_rb_insert(vma, mm); > + mm_write_sequnlock(mm); > } > > static void __vma_link_file(struct vm_area_struct *vma) > @@ -680,7 +706,7 @@ static __always_inline void __vma_unlink_common(struct mm_struct *mm, > { > struct vm_area_struct *next; > > - vma_rb_erase_ignore(vma, &mm->mm_rb, ignore); > + vma_rb_erase_ignore(vma, mm, ignore); > next = vma->vm_next; > if (has_prev) > prev->vm_next = next; > @@ -2674,7 +2700,7 @@ detach_vmas_to_be_unmapped(struct mm_struct *mm, struct vm_area_struct *vma, > insertion_point = (prev ? &prev->vm_next : &mm->mmap); > vma->vm_prev = NULL; > do { > - vma_rb_erase(vma, &mm->mm_rb); > + vma_rb_erase(vma, mm); > mm->map_count--; > tail_vma = vma; > vma = vma->vm_next; > -- > 2.21.0 >
