On Thu, 06 Aug 2015, Vlastimil Babka wrote:
...
diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c index ca1e091..38d69fc 100644 --- a/fs/proc/task_mmu.c +++ b/fs/proc/task_mmu.c @@ -579,6 +579,7 @@ static void show_smap_vma_flags(struct seq_file *m, struct vm_area_struct *vma)
This function has the following comment:
Don't forget to update Documentation/ on changes.
[...]
--- a/mm/gup.c +++ b/mm/gup.c @@ -92,7 +92,7 @@ retry: */ mark_page_accessed(page); }
- if ((flags & FOLL_POPULATE) && (vma->vm_flags & VM_LOCKED)) {
- if ((flags & FOLL_MLOCK) && (vma->vm_flags & VM_LOCKED)) { /*
- The preliminary mapping check is mainly to avoid the
- pointless overhead of lock_page on the ZERO_PAGE
@@ -265,6 +265,9 @@ static int faultin_page(struct task_struct *tsk, struct vm_area_struct *vma, unsigned int fault_flags = 0; int ret;
- /* mlock all present pages, but do not fault in new pages */
- if ((*flags & (FOLL_POPULATE | FOLL_MLOCK)) == FOLL_MLOCK)
return -ENOENT;@@ -850,7 +853,10 @@ long populate_vma_page_range(struct vm_area_struct *vma, VM_BUG_ON_VMA(end > vma->vm_end, vma); VM_BUG_ON_MM(!rwsem_is_locked(&mm->mmap_sem), mm);
- gup_flags = FOLL_TOUCH | FOLL_POPULATE;
- gup_flags = FOLL_TOUCH | FOLL_MLOCK;
- if ((vma->vm_flags & (VM_LOCKED | VM_LOCKONFAULT)) == VM_LOCKED)
gup_flags |= FOLL_POPULATE;- /*
- We want to touch writable mappings with a write fault in order
- to break COW, except for shared mappings because these don't COW
I think this might be breaking the populate part of mmap(MAP_POPULATE & ~MAP_LOCKED) case, if I follow the execution correctly (it's far from simple...)
SYSCALL_DEFINE6(mmap_pgoff... with MAP_POPULATE vm_mmap_pgoff(..., MAP_POPULATE...) do_mmap_pgoff(...MAP_POPULATE... &populate) -> populate == TRUE mm_populate() __mm_populate() populate_vma_page_range()
Previously, this path would have FOLL_POPULATE in gup_flags and continue with __get_user_pages() and faultin_page() (actually regardless of FOLL_POPULATE) which would fault in the pages.
After your patch, populate_vma_page_range() will set FOLL_MLOCK, but since VM_LOCKED is not set, FOLL_POPULATE won't be set either. Then faultin_page() will return on the new check:
flags & (FOLL_POPULATE | FOLL_MLOCK)) == FOLL_MLOCK
I am on vacation atm but I will try and get to respin this series after making sure there aren't any more FOLL flag issues.
Thanks for keeping with these :)
Eric