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 <[email protected]> */ -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; }
