mirrors
/
linux-stable
mirror of https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
1
0
Fork 0
Code Issues Releases Wiki Activity

mm/munlock: mlock_pte_range() when mlocking or munlocking 

Fill in missing pieces: reimplementation of munlock_vma_pages_range(),
required to lower the mlock_counts when munlocking without munmapping;
and its complement, implementation of mlock_vma_pages_range(), required
to raise the mlock_counts on pages already there when a range is mlocked.

Combine them into just the one function mlock_vma_pages_range(), using
walk_page_range() to run mlock_pte_range().  This approach fixes the
"Very slow unlockall()" of unpopulated PROT_NONE areas, reported in
https://lore.kernel.org/linux-mm/70885d37-62b7-748b-29df-9e94f3291736@gmail.com/

Munlock clears VM_LOCKED at the start, under exclusive mmap_lock; but if
a racing truncate or holepunch (depending on i_mmap_rwsem) gets to the
pte first, it will not try to munlock the page: leaving release_pages()
to correct it when the last reference to the page is gone - that's okay,
a page is not evictable anyway while it is held by an extra reference.

Mlock sets VM_LOCKED at the start, under exclusive mmap_lock; but if
a racing remove_migration_pte() or try_to_unmap_one() (depending on
i_mmap_rwsem) gets to the pte first, it will try to mlock the page,
then mlock_pte_range() mlock it a second time.  This is harder to
reproduce, but a more serious race because it could leave the page
unevictable indefinitely though the area is munlocked afterwards.
Guard against it by setting the (inappropriate) VM_IO flag,
and modifying mlock_vma_page() to decline such vmas.

Signed-off-by: Hugh Dickins <hughd@google.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
This commit is contained in:
Hugh Dickins 2022-02-14 18:31:48 -08:00 committed by Matthew Wilcox (Oracle)
parent 07ca760673
commit 34b6792380
2 changed files with 96 additions and 28 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

3
mm/internal.h
View File

@ -412,7 +412,8 @@ void mlock_page(struct page *page);
static inline void mlock_vma_page(struct page *page,
struct vm_area_struct *vma, bool compound)
{
if (unlikely(vma->vm_flags & VM_LOCKED) &&
/* VM_IO check prevents migration from double-counting during mlock */
if (unlikely((vma->vm_flags & (VM_LOCKED|VM_IO)) == VM_LOCKED) &&
(compound || !PageTransCompound(page)))
mlock_page(page);
}

121
mm/mlock.c
View File

@ -14,6 +14,7 @@
#include <linux/swapops.h>
#include <linux/pagemap.h>
#include <linux/pagevec.h>
#include <linux/pagewalk.h>
#include <linux/mempolicy.h>
#include <linux/syscalls.h>
#include <linux/sched.h>
@ -127,25 +128,91 @@ out:
unlock_page_memcg(page);
}
/*
* munlock_vma_pages_range() - munlock all pages in the vma range.'
* @vma - vma containing range to be munlock()ed.
* @start - start address in @vma of the range
* @end - end of range in @vma.
*
* For mremap(), munmap() and exit().
*
* Called with @vma VM_LOCKED.
*
* Returns with VM_LOCKED cleared. Callers must be prepared to
* deal with this.
*/
static void munlock_vma_pages_range(struct vm_area_struct *vma,
unsigned long start, unsigned long end)
{
vma->vm_flags &= VM_LOCKED_CLEAR_MASK;
static int mlock_pte_range(pmd_t *pmd, unsigned long addr,
unsigned long end, struct mm_walk *walk)
/* Reimplementation to follow in later commit */
{
struct vm_area_struct *vma = walk->vma;
spinlock_t *ptl;
pte_t *start_pte, *pte;
struct page *page;
ptl = pmd_trans_huge_lock(pmd, vma);
if (ptl) {
if (!pmd_present(*pmd))
goto out;
if (is_huge_zero_pmd(*pmd))
goto out;
page = pmd_page(*pmd);
if (vma->vm_flags & VM_LOCKED)
mlock_page(page);
else
munlock_page(page);
goto out;
}
start_pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
for (pte = start_pte; addr != end; pte++, addr += PAGE_SIZE) {
if (!pte_present(*pte))
continue;
page = vm_normal_page(vma, addr, *pte);
if (!page)
continue;
if (PageTransCompound(page))
continue;
if (vma->vm_flags & VM_LOCKED)
mlock_page(page);
else
munlock_page(page);
}
pte_unmap(start_pte);
out:
spin_unlock(ptl);
cond_resched();
return 0;
}
/*
* mlock_vma_pages_range() - mlock any pages already in the range,
* or munlock all pages in the range.
* @vma - vma containing range to be mlock()ed or munlock()ed
* @start - start address in @vma of the range
* @end - end of range in @vma
* @newflags - the new set of flags for @vma.
*
* Called for mlock(), mlock2() and mlockall(), to set @vma VM_LOCKED;
* called for munlock() and munlockall(), to clear VM_LOCKED from @vma.
*/
static void mlock_vma_pages_range(struct vm_area_struct *vma,
unsigned long start, unsigned long end, vm_flags_t newflags)
{
static const struct mm_walk_ops mlock_walk_ops = {
.pmd_entry = mlock_pte_range,
};
/*
* There is a slight chance that concurrent page migration,
* or page reclaim finding a page of this now-VM_LOCKED vma,
* will call mlock_vma_page() and raise page's mlock_count:
* double counting, leaving the page unevictable indefinitely.
* Communicate this danger to mlock_vma_page() with VM_IO,
* which is a VM_SPECIAL flag not allowed on VM_LOCKED vmas.
* mmap_lock is held in write mode here, so this weird
* combination should not be visible to other mmap_lock users;
* but WRITE_ONCE so rmap walkers must see VM_IO if VM_LOCKED.
*/
if (newflags & VM_LOCKED)
newflags |= VM_IO;
WRITE_ONCE(vma->vm_flags, newflags);
lru_add_drain();
walk_page_range(vma->vm_mm, start, end, &mlock_walk_ops, NULL);
lru_add_drain();
if (newflags & VM_IO) {
newflags &= ~VM_IO;
WRITE_ONCE(vma->vm_flags, newflags);
}
}
/*
@ -164,10 +231,9 @@ static int mlock_fixup(struct vm_area_struct *vma, struct vm_area_struct **prev,
pgoff_t pgoff;
int nr_pages;
int ret = 0;
int lock = !!(newflags & VM_LOCKED);
vm_flags_t old_flags = vma->vm_flags;
vm_flags_t oldflags = vma->vm_flags;
if (newflags == vma->vm_flags || (vma->vm_flags & VM_SPECIAL) ||
if (newflags == oldflags || (oldflags & VM_SPECIAL) ||
is_vm_hugetlb_page(vma) || vma == get_gate_vma(current->mm) ||
vma_is_dax(vma) || vma_is_secretmem(vma))
/* don't set VM_LOCKED or VM_LOCKONFAULT and don't count */
@ -199,9 +265,9 @@ success:
* Keep track of amount of locked VM.
*/
nr_pages = (end - start) >> PAGE_SHIFT;
if (!lock)
if (!(newflags & VM_LOCKED))
nr_pages = -nr_pages;
else if (old_flags & VM_LOCKED)
else if (oldflags & VM_LOCKED)
nr_pages = 0;
mm->locked_vm += nr_pages;
@ -211,11 +277,12 @@ success:
* set VM_LOCKED, populate_vma_page_range will bring it back.
*/
if (lock)
if ((newflags & VM_LOCKED) && (oldflags & VM_LOCKED)) {
/* No work to do, and mlocking twice would be wrong */
vma->vm_flags = newflags;
else
munlock_vma_pages_range(vma, start, end);
} else {
mlock_vma_pages_range(vma, start, end, newflags);
}
out:
*prev = vma;
return ret;