On Wed, Aug 15, 2018 at 02:54:13PM -0700, Yang Shi wrote:
>
>
> On 8/15/18 2:09 PM, Matthew Wilcox wrote:
> > On Wed, Aug 15, 2018 at 12:16:06PM -0700, Matthew Wilcox wrote:
> > > (not even compiled, and I can see a good opportunity for combining the
> > > VM_LOCKED loop with the has_uprobes loop)
> > I was rushing to get that sent earlier. Here it is tidied up to
> > actually compile.
>
> Thanks for the example. Yes, I believe the code still can be compacted to
> save some lines. However, the cover letter and the commit log of this patch
> has elaborated the discussion in the earlier reviews about why we do it in
> this way.
You mean the other callers which need to hold mmap_sem write-locked for
longer? I hadn't really considered those; how about this?
mmap.c | 47 +++++++++++++++++++++++++++++------------------
1 file changed, 29 insertions(+), 18 deletions(-)
diff --git a/mm/mmap.c b/mm/mmap.c
index de699523c0b7..06dc31d1da8c 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2798,11 +2798,11 @@ int split_vma(struct mm_struct *mm, struct vm_area_struct *vma,
* work. This now handles partial unmappings.
* Jeremy Fitzhardinge <jeremy@xxxxxxxx>
*/
-int do_munmap(struct mm_struct *mm, unsigned long start, size_t len,
- struct list_head *uf)
+static int __do_munmap(struct mm_struct *mm, unsigned long start, size_t len,
+ struct list_head *uf, bool downgrade)
{
unsigned long end;
- struct vm_area_struct *vma, *prev, *last;
+ struct vm_area_struct *vma, *prev, *last, *tmp;
if ((offset_in_page(start)) || start > TASK_SIZE || len > TASK_SIZE-start)
return -EINVAL;
@@ -2816,7 +2816,7 @@ int do_munmap(struct mm_struct *mm, unsigned long start, size_t len,
if (!vma)
return 0;
prev = vma->vm_prev;
- /* we have start < vma->vm_end */
+ /* we have start < vma->vm_end */
/* if it doesn't overlap, we have nothing.. */
end = start + len;
@@ -2873,18 +2873,22 @@ int do_munmap(struct mm_struct *mm, unsigned long start, size_t len,
/*
* unlock any mlock()ed ranges before detaching vmas
+ * and check to see if there's any reason we might have to hold
+ * the mmap_sem write-locked while unmapping regions.
*/
- if (mm->locked_vm) {
- struct vm_area_struct *tmp = vma;
- while (tmp && tmp->vm_start < end) {
- if (tmp->vm_flags & VM_LOCKED) {
- mm->locked_vm -= vma_pages(tmp);
- munlock_vma_pages_all(tmp);
- }
- tmp = tmp->vm_next;
+ for (tmp = vma; tmp && tmp->vm_start < end; tmp = tmp->vm_next) {
+ if (tmp->vm_flags & VM_LOCKED) {
+ mm->locked_vm -= vma_pages(tmp);
+ munlock_vma_pages_all(tmp);
}
+ if (tmp->vm_file &&
+ has_uprobes(tmp, tmp->vm_start, tmp->vm_end))
+ downgrade = false;
}
+ if (downgrade)
+ downgrade_write(&mm->mmap_sem);
+
/*
* Remove the vma's, and unmap the actual pages
*/
@@ -2896,7 +2900,13 @@ int do_munmap(struct mm_struct *mm, unsigned long start, size_t len,
/* Fix up all other VM information */
remove_vma_list(mm, vma);
- return 0;
+ return downgrade ? 1 : 0;
+}
+
+int do_unmap(struct mm_struct *mm, unsigned long start, size_t len,
+ struct list_head *uf)
+{
+ return __do_munmap(mm, start, len, uf, false);
}
int vm_munmap(unsigned long start, size_t len)
@@ -2905,11 +2915,12 @@ int vm_munmap(unsigned long start, size_t len)
struct mm_struct *mm = current->mm;
LIST_HEAD(uf);
- if (down_write_killable(&mm->mmap_sem))
- return -EINTR;
-
- ret = do_munmap(mm, start, len, &uf);
- up_write(&mm->mmap_sem);
+ down_write(&mm->mmap_sem);
+ ret = __do_munmap(mm, start, len, &uf, true);
+ if (ret == 1)
+ up_read(&mm->mmap_sem);
+ else
+ up_write(&mm->mmap_sem);
userfaultfd_unmap_complete(mm, &uf);
return ret;
}
