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Message-ID: <20220125204741.jklejdjbrwxqq67t@revolver>
Date: Tue, 25 Jan 2022 20:47:50 +0000
From: Liam Howlett <liam.howlett@...cle.com>
To: Vlastimil Babka <vbabka@...e.cz>
CC: "maple-tree@...ts.infradead.org" <maple-tree@...ts.infradead.org>,
"linux-mm@...ck.org" <linux-mm@...ck.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Song Liu <songliubraving@...com>,
Davidlohr Bueso <dave@...olabs.net>,
"Paul E . McKenney" <paulmck@...nel.org>,
Matthew Wilcox <willy@...radead.org>,
Laurent Dufour <ldufour@...ux.ibm.com>,
David Rientjes <rientjes@...gle.com>,
Axel Rasmussen <axelrasmussen@...gle.com>,
Suren Baghdasaryan <surenb@...gle.com>,
Rik van Riel <riel@...riel.com>,
Peter Zijlstra <peterz@...radead.org>,
Michel Lespinasse <walken.cr@...il.com>,
Jerome Glisse <jglisse@...hat.com>,
Minchan Kim <minchan@...gle.com>,
Joel Fernandes <joelaf@...gle.com>,
Rom Lemarchand <romlem@...gle.com>
Subject: Re: [PATCH v4 43/66] userfaultfd: Use maple tree iterator to iterate
VMAs
* Vlastimil Babka <vbabka@...e.cz> [220119 11:26]:
> On 12/1/21 15:30, Liam Howlett wrote:
> > From: "Liam R. Howlett" <Liam.Howlett@...cle.com>
> >
> > Don't use the mm_struct linked list or the vma->vm_next in prep for removal
> >
> > Signed-off-by: Liam R. Howlett <Liam.Howlett@...cle.com>
> > ---
> > fs/userfaultfd.c | 49 ++++++++++++++++++++++-------------
> > include/linux/userfaultfd_k.h | 7 +++--
> > mm/mmap.c | 12 ++++-----
> > 3 files changed, 40 insertions(+), 28 deletions(-)
> >
> > diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
> > index 22bf14ab2d16..2880025598c7 100644
> > --- a/fs/userfaultfd.c
> > +++ b/fs/userfaultfd.c
> > @@ -606,14 +606,16 @@ static void userfaultfd_event_wait_completion(struct userfaultfd_ctx *ctx,
> > if (release_new_ctx) {
> > struct vm_area_struct *vma;
> > struct mm_struct *mm = release_new_ctx->mm;
> > + VMA_ITERATOR(vmi, mm, 0);
> >
> > /* the various vma->vm_userfaultfd_ctx still points to it */
> > mmap_write_lock(mm);
> > - for (vma = mm->mmap; vma; vma = vma->vm_next)
> > + for_each_vma(vmi, vma) {
> > if (vma->vm_userfaultfd_ctx.ctx == release_new_ctx) {
> > vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
> > vma->vm_flags &= ~__VM_UFFD_FLAGS;
> > }
> > + }
> > mmap_write_unlock(mm);
> >
> > userfaultfd_ctx_put(release_new_ctx);
> > @@ -794,11 +796,13 @@ static bool has_unmap_ctx(struct userfaultfd_ctx *ctx, struct list_head *unmaps,
> > return false;
> > }
> >
> > -int userfaultfd_unmap_prep(struct vm_area_struct *vma,
> > - unsigned long start, unsigned long end,
> > - struct list_head *unmaps)
> > +int userfaultfd_unmap_prep(struct mm_struct *mm, unsigned long start,
> > + unsigned long end, struct list_head *unmaps)
> > {
> > - for ( ; vma && vma->vm_start < end; vma = vma->vm_next) {
> > + VMA_ITERATOR(vmi, mm, start);
> > + struct vm_area_struct *vma;
> > +
> > + for_each_vma_range(vmi, vma, end) {
> > struct userfaultfd_unmap_ctx *unmap_ctx;
> > struct userfaultfd_ctx *ctx = vma->vm_userfaultfd_ctx.ctx;
> >
> > @@ -848,6 +852,7 @@ static int userfaultfd_release(struct inode *inode, struct file *file)
> > /* len == 0 means wake all */
> > struct userfaultfd_wake_range range = { .len = 0, };
> > unsigned long new_flags;
> > + MA_STATE(mas, &mm->mm_mt, 0, 0);
>
> Again, it looks like this could also be VMA_ITERATOR, consistent with the
> one above?
VMA_ITERATOR is for simple cases, this is not a simple case, but in this
change it does appear so. I missed the mas_pause() when the state is
invalidated by vma_merge() success in the mas_for_each() loop below. I
will fix this.
>
> >
> > WRITE_ONCE(ctx->released, true);
> >
> > @@ -864,7 +869,7 @@ static int userfaultfd_release(struct inode *inode, struct file *file)
> > */
> > mmap_write_lock(mm);
> > prev = NULL;
> > - for (vma = mm->mmap; vma; vma = vma->vm_next) {
> > + mas_for_each(&mas, vma, ULONG_MAX) {
> > cond_resched();
> > BUG_ON(!!vma->vm_userfaultfd_ctx.ctx ^
> > !!(vma->vm_flags & __VM_UFFD_FLAGS));
> > @@ -1281,6 +1286,7 @@ static int userfaultfd_register(struct userfaultfd_ctx *ctx,
> > bool found;
> > bool basic_ioctls;
> > unsigned long start, end, vma_end;
> > + MA_STATE(mas, &mm->mm_mt, 0, 0);
> >
> > user_uffdio_register = (struct uffdio_register __user *) arg;
> >
> > @@ -1323,7 +1329,8 @@ static int userfaultfd_register(struct userfaultfd_ctx *ctx,
> > goto out;
> >
> > mmap_write_lock(mm);
> > - vma = find_vma_prev(mm, start, &prev);
> > + mas_set(&mas, start);
> > + vma = mas_find(&mas, ULONG_MAX);
> > if (!vma)
> > goto out_unlock;
> >
> > @@ -1348,7 +1355,7 @@ static int userfaultfd_register(struct userfaultfd_ctx *ctx,
> > */
> > found = false;
> > basic_ioctls = false;
> > - for (cur = vma; cur && cur->vm_start < end; cur = cur->vm_next) {
> > + for (cur = vma; cur; cur = mas_next(&mas, end - 1)) {
> > cond_resched();
> >
> > BUG_ON(!!cur->vm_userfaultfd_ctx.ctx ^
> > @@ -1408,8 +1415,10 @@ static int userfaultfd_register(struct userfaultfd_ctx *ctx,
> > }
> > BUG_ON(!found);
> >
> > - if (vma->vm_start < start)
> > - prev = vma;
> > + mas_set(&mas, start);
> > + prev = mas_prev(&mas, 0);
> > + if (prev != vma)
> > + mas_next(&mas, ULONG_MAX);
>
> Hmm non-commented tricky stuff...
Oh, I did not see this as tricky. I will add a comment. Basically, I
am setting the maple state to search for start, then a mas_prev() means
it will get the vma before start.
>
> >
> > ret = 0;
> > do {
> > @@ -1466,8 +1475,8 @@ static int userfaultfd_register(struct userfaultfd_ctx *ctx,
> > skip:
> > prev = vma;
> > start = vma->vm_end;
> > - vma = vma->vm_next;
> > - } while (vma && vma->vm_start < end);
> > + vma = mas_next(&mas, end - 1);
> > + } while (vma);
> > out_unlock:
> > mmap_write_unlock(mm);
> > mmput(mm);
> > @@ -1511,6 +1520,7 @@ static int userfaultfd_unregister(struct userfaultfd_ctx *ctx,
> > bool found;
> > unsigned long start, end, vma_end;
> > const void __user *buf = (void __user *)arg;
> > + MA_STATE(mas, &mm->mm_mt, 0, 0);
> >
> > ret = -EFAULT;
> > if (copy_from_user(&uffdio_unregister, buf, sizeof(uffdio_unregister)))
> > @@ -1529,7 +1539,8 @@ static int userfaultfd_unregister(struct userfaultfd_ctx *ctx,
> > goto out;
> >
> > mmap_write_lock(mm);
> > - vma = find_vma_prev(mm, start, &prev);
> > + mas_set(&mas, start);
> > + vma = mas_find(&mas, ULONG_MAX);
> > if (!vma)
> > goto out_unlock;
> >
> > @@ -1554,7 +1565,7 @@ static int userfaultfd_unregister(struct userfaultfd_ctx *ctx,
> > */
> > found = false;
> > ret = -EINVAL;
> > - for (cur = vma; cur && cur->vm_start < end; cur = cur->vm_next) {
> > + for (cur = vma; cur; cur = mas_next(&mas, end - 1)) {
> > cond_resched();
> >
> > BUG_ON(!!cur->vm_userfaultfd_ctx.ctx ^
> > @@ -1574,8 +1585,10 @@ static int userfaultfd_unregister(struct userfaultfd_ctx *ctx,
> > }
> > BUG_ON(!found);
> >
> > - if (vma->vm_start < start)
> > - prev = vma;
> > + mas_set(&mas, start);
> > + prev = mas_prev(&mas, 0);
> > + if (prev != vma)
> > + mas_next(&mas, ULONG_MAX);
>
> Same here.
I'll add the comment here too.
>
> >
> > ret = 0;
> > do {
> > @@ -1640,8 +1653,8 @@ static int userfaultfd_unregister(struct userfaultfd_ctx *ctx,
> > skip:
> > prev = vma;
> > start = vma->vm_end;
> > - vma = vma->vm_next;
> > - } while (vma && vma->vm_start < end);
> > + vma = mas_next(&mas, end - 1);
> > + } while (vma);
> > out_unlock:
> > mmap_write_unlock(mm);
> > mmput(mm);
> > diff --git a/include/linux/userfaultfd_k.h b/include/linux/userfaultfd_k.h
> > index 33cea484d1ad..e0b2ec2c20f2 100644
> > --- a/include/linux/userfaultfd_k.h
> > +++ b/include/linux/userfaultfd_k.h
> > @@ -139,9 +139,8 @@ extern bool userfaultfd_remove(struct vm_area_struct *vma,
> > unsigned long start,
> > unsigned long end);
> >
> > -extern int userfaultfd_unmap_prep(struct vm_area_struct *vma,
> > - unsigned long start, unsigned long end,
> > - struct list_head *uf);
> > +extern int userfaultfd_unmap_prep(struct mm_struct *mm, unsigned long start,
> > + unsigned long end, struct list_head *uf);
> > extern void userfaultfd_unmap_complete(struct mm_struct *mm,
> > struct list_head *uf);
> >
> > @@ -222,7 +221,7 @@ static inline bool userfaultfd_remove(struct vm_area_struct *vma,
> > return true;
> > }
> >
> > -static inline int userfaultfd_unmap_prep(struct vm_area_struct *vma,
> > +static inline int userfaultfd_unmap_prep(struct mm_struct *mm,
> > unsigned long start, unsigned long end,
> > struct list_head *uf)
> > {
> > diff --git a/mm/mmap.c b/mm/mmap.c
> > index 79b8494d83c6..dde74e0b195d 100644
> > --- a/mm/mmap.c
> > +++ b/mm/mmap.c
> > @@ -2449,7 +2449,7 @@ do_mas_align_munmap(struct ma_state *mas, struct vm_area_struct *vma,
> > * split, despite we could. This is unlikely enough
> > * failure that it's not worth optimizing it for.
> > */
> > - int error = userfaultfd_unmap_prep(vma, start, end, uf);
> > + int error = userfaultfd_unmap_prep(mm, start, end, uf);
> >
> > if (error)
> > return error;
> > @@ -2938,10 +2938,7 @@ static int do_brk_munmap(struct ma_state *mas, struct vm_area_struct *vma,
> > goto munmap_full_vma;
> > }
> >
> > - vma_init(&unmap, mm);
> > - unmap.vm_start = newbrk;
> > - unmap.vm_end = oldbrk;
> > - ret = userfaultfd_unmap_prep(&unmap, newbrk, oldbrk, uf);
> > + ret = userfaultfd_unmap_prep(mm, newbrk, oldbrk, uf);
> > if (ret)
> > return ret;
> > ret = 1;
> > @@ -2954,6 +2951,9 @@ static int do_brk_munmap(struct ma_state *mas, struct vm_area_struct *vma,
> > }
> >
> > vma->vm_end = newbrk;
> > + vma_init(&unmap, mm);
> > + unmap.vm_start = newbrk;
> > + unmap.vm_end = oldbrk;
> > if (vma_mas_remove(&unmap, mas))
> > goto mas_store_fail;
> >
> > @@ -2963,7 +2963,7 @@ static int do_brk_munmap(struct ma_state *mas, struct vm_area_struct *vma,
> > }
> >
> > unmap_pages = vma_pages(&unmap);
> > - if (unmap.vm_flags & VM_LOCKED) {
> > + if (vma->vm_flags & VM_LOCKED) {
>
> Hmm is this an unrelated bug fix? As unmap didn't have any vm_flags set even
> before this patch, right?
Yes. Thanks, I must have merged it into the wrong commit.
>
> > mm->locked_vm -= unmap_pages;
> > munlock_vma_pages_range(&unmap, newbrk, oldbrk);
> > }
>
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