linux-toradex.git/mm/gup.c, branch v4.1.10

mm: use READ_ONCE() for non-scalar types

2015-04-15T23:35:18+00:00

Commit 38c5ce936a08 ("mm/gup: Replace ACCESS_ONCE with READ_ONCE")
converted ACCESS_ONCE usage in gup_pmd_range() to READ_ONCE, since
ACCESS_ONCE doesn't work reliably on non-scalar types.

This patch also fixes the other ACCESS_ONCE usages in gup_pte_range()
and __get_user_pages_fast() in mm/gup.c

Signed-off-by: Jason Low 
Acked-by: Michal Hocko 
Acked-by: Davidlohr Bueso 
Acked-by: Rik van Riel 
Reviewed-by: Christian Borntraeger 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm: move mm_populate()-related code to mm/gup.c

2015-04-14T23:49:00+00:00

It's odd that we have populate_vma_page_range() and __mm_populate() in
mm/mlock.c.  It's implementation of generic memory population and mlocking
is one of possible side effect, if VM_LOCKED is set.

__get_user_pages() is core of the implementation.  Let's move the code
into mm/gup.c.

Signed-off-by: Kirill A. Shutemov 
Acked-by: Linus Torvalds 
Acked-by: David Rientjes 
Cc: Michel Lespinasse 
Cc: Rik van Riel 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm: rename FOLL_MLOCK to FOLL_POPULATE

2015-04-14T23:48:59+00:00

After commit a1fde08c74e9 ("VM: skip the stack guard page lookup in
get_user_pages only for mlock") FOLL_MLOCK has lost its original
meaning: we don't necessarily mlock the page if the flags is set -- we
also take VM_LOCKED into consideration.

Since we use the same codepath for __mm_populate(), let's rename
FOLL_MLOCK to FOLL_POPULATE.

Signed-off-by: Kirill A. Shutemov 
Acked-by: Linus Torvalds 
Acked-by: David Rientjes 
Cc: Michel Lespinasse 
Cc: Rik van Riel 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

Merge tag 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/borntraeger/linux

2015-02-14T18:54:28+00:00

Pull ACCESS_ONCE() rule tightening from Christian Borntraeger:
 "Tighten rules for ACCESS_ONCE

  This series tightens the rules for ACCESS_ONCE to only work on scalar
  types.  It also contains the necessary fixups as indicated by build
  bots of linux-next.  Now everything is in place to prevent new
  non-scalar users of ACCESS_ONCE and we can continue to convert code to
  READ_ONCE/WRITE_ONCE"

* tag 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/borntraeger/linux:
  kernel: Fix sparse warning for ACCESS_ONCE
  next: sh: Fix compile error
  kernel: tighten rules for ACCESS ONCE
  mm/gup: Replace ACCESS_ONCE with READ_ONCE
  x86/spinlock: Leftover conversion ACCESS_ONCE->READ_ONCE
  x86/xen/p2m: Replace ACCESS_ONCE with READ_ONCE
  ppc/hugetlbfs: Replace ACCESS_ONCE with READ_ONCE
  ppc/kvm: Replace ACCESS_ONCE with READ_ONCE

mm: convert p[te|md]_numa users to p[te|md]_protnone_numa

2015-02-13T02:54:08+00:00

Convert existing users of pte_numa and friends to the new helper.  Note
that the kernel is broken after this patch is applied until the other page
table modifiers are also altered.  This patch layout is to make review
easier.

Signed-off-by: Mel Gorman 
Acked-by: Linus Torvalds 
Acked-by: Aneesh Kumar 
Acked-by: Benjamin Herrenschmidt 
Tested-by: Sasha Levin 
Cc: Dave Jones 
Cc: Hugh Dickins 
Cc: Ingo Molnar 
Cc: Kirill Shutemov 
Cc: Paul Mackerras 
Cc: Rik van Riel 
Cc: Sasha Levin 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm: gup: use get_user_pages_unlocked within get_user_pages_fast

2015-02-12T01:06:05+00:00

This allows the get_user_pages_fast slow path to release the mmap_sem
before blocking.

Signed-off-by: Andrea Arcangeli 
Reviewed-by: Kirill A. Shutemov 
Cc: Andres Lagar-Cavilla 
Cc: Peter Feiner 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm: gup: add __get_user_pages_unlocked to customize gup_flags

2015-02-12T01:06:05+00:00

Some callers (like KVM) may want to set the gup_flags like FOLL_HWPOSION
to get a proper -EHWPOSION retval instead of -EFAULT to take a more
appropriate action if get_user_pages runs into a memory failure.

Signed-off-by: Andrea Arcangeli 
Reviewed-by: Kirill A. Shutemov 
Cc: Andres Lagar-Cavilla 
Cc: Peter Feiner 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm: gup: add get_user_pages_locked and get_user_pages_unlocked

2015-02-12T01:06:05+00:00

FAULT_FOLL_ALLOW_RETRY allows the page fault to drop the mmap_sem for
reading to reduce the mmap_sem contention (for writing), like while
waiting for I/O completion.  The problem is that right now practically no
get_user_pages call uses FAULT_FOLL_ALLOW_RETRY, so we're not leveraging
that nifty feature.

Andres fixed it for the KVM page fault.  However get_user_pages_fast
remains uncovered, and 99% of other get_user_pages aren't using it either
(the only exception being FOLL_NOWAIT in KVM which is really nonblocking
and in fact it doesn't even release the mmap_sem).

So this patchsets extends the optimization Andres did in the KVM page
fault to the whole kernel.  It makes most important places (including
gup_fast) to use FAULT_FOLL_ALLOW_RETRY to reduce the mmap_sem hold times
during I/O.

The only few places that remains uncovered are drivers like v4l and other
exceptions that tends to work on their own memory and they're not working
on random user memory (for example like O_DIRECT that uses gup_fast and is
fully covered by this patch).

A follow up patch should probably also add a printk_once warning to
get_user_pages that should go obsolete and be phased out eventually.  The
"vmas" parameter of get_user_pages makes it fundamentally incompatible
with FAULT_FOLL_ALLOW_RETRY (vmas array becomes meaningless the moment the
mmap_sem is released).

While this is just an optimization, this becomes an absolute requirement
for the userfaultfd feature http://lwn.net/Articles/615086/ .

The userfaultfd allows to block the page fault, and in order to do so I
need to drop the mmap_sem first.  So this patch also ensures that all
memory where userfaultfd could be registered by KVM, the very first fault
(no matter if it is a regular page fault, or a get_user_pages) always has
FAULT_FOLL_ALLOW_RETRY set.  Then the userfaultfd blocks and it is waken
only when the pagetable is already mapped.  The second fault attempt after
the wakeup doesn't need FAULT_FOLL_ALLOW_RETRY, so it's ok to retry
without it.

This patch (of 5):

We can leverage the VM_FAULT_RETRY functionality in the page fault paths
better by using either get_user_pages_locked or get_user_pages_unlocked.

The former allows conversion of get_user_pages invocations that will have
to pass a "&locked" parameter to know if the mmap_sem was dropped during
the call.  Example from:

    down_read(&mm->mmap_sem);
    do_something()
    get_user_pages(tsk, mm, ..., pages, NULL);
    up_read(&mm->mmap_sem);

to:

    int locked = 1;
    down_read(&mm->mmap_sem);
    do_something()
    get_user_pages_locked(tsk, mm, ..., pages, &locked);
    if (locked)
        up_read(&mm->mmap_sem);

The latter is suitable only as a drop in replacement of the form:

    down_read(&mm->mmap_sem);
    get_user_pages(tsk, mm, ..., pages, NULL);
    up_read(&mm->mmap_sem);

into:

    get_user_pages_unlocked(tsk, mm, ..., pages);

Where tsk, mm, the intermediate "..." paramters and "pages" can be any
value as before.  Just the last parameter of get_user_pages (vmas) must be
NULL for get_user_pages_locked|unlocked to be usable (the latter original
form wouldn't have been safe anyway if vmas wasn't null, for the former we
just make it explicit by dropping the parameter).

If vmas is not NULL these two methods cannot be used.

Signed-off-by: Andrea Arcangeli 
Reviewed-by: Andres Lagar-Cavilla 
Reviewed-by: Peter Feiner 
Reviewed-by: Kirill A. Shutemov 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm/hugetlb: take page table lock in follow_huge_pmd()

2015-02-12T01:06:01+00:00

We have a race condition between move_pages() and freeing hugepages, where
move_pages() calls follow_page(FOLL_GET) for hugepages internally and
tries to get its refcount without preventing concurrent freeing.  This
race crashes the kernel, so this patch fixes it by moving FOLL_GET code
for hugepages into follow_huge_pmd() with taking the page table lock.

This patch intentionally removes page==NULL check after pte_page.
This is justified because pte_page() never returns NULL for any
architectures or configurations.

This patch changes the behavior of follow_huge_pmd() for tail pages and
then tail pages can be pinned/returned.  So the caller must be changed to
properly handle the returned tail pages.

We could have a choice to add the similar locking to
follow_huge_(addr|pud) for consistency, but it's not necessary because
currently these functions don't support FOLL_GET flag, so let's leave it
for future development.

Here is the reproducer:

  $ cat movepages.c
  #include 
  #include 
  #include 

  #define ADDR_INPUT      0x700000000000UL
  #define HPS             0x200000
  #define PS              0x1000

  int main(int argc, char *argv[]) {
          int i;
          int nr_hp = strtol(argv[1], NULL, 0);
          int nr_p  = nr_hp * HPS / PS;
          int ret;
          void **addrs;
          int *status;
          int *nodes;
          pid_t pid;

          pid = strtol(argv[2], NULL, 0);
          addrs  = malloc(sizeof(char *) * nr_p + 1);
          status = malloc(sizeof(char *) * nr_p + 1);
          nodes  = malloc(sizeof(char *) * nr_p + 1);

          while (1) {
                  for (i = 0; i < nr_p; i++) {
                          addrs[i] = (void *)ADDR_INPUT + i * PS;
                          nodes[i] = 1;
                          status[i] = 0;
                  }
                  ret = numa_move_pages(pid, nr_p, addrs, nodes, status,
                                        MPOL_MF_MOVE_ALL);
                  if (ret == -1)
                          err("move_pages");

                  for (i = 0; i < nr_p; i++) {
                          addrs[i] = (void *)ADDR_INPUT + i * PS;
                          nodes[i] = 0;
                          status[i] = 0;
                  }
                  ret = numa_move_pages(pid, nr_p, addrs, nodes, status,
                                        MPOL_MF_MOVE_ALL);
                  if (ret == -1)
                          err("move_pages");
          }
          return 0;
  }

  $ cat hugepage.c
  #include 
  #include 
  #include 

  #define ADDR_INPUT      0x700000000000UL
  #define HPS             0x200000

  int main(int argc, char *argv[]) {
          int nr_hp = strtol(argv[1], NULL, 0);
          char *p;

          while (1) {
                  p = mmap((void *)ADDR_INPUT, nr_hp * HPS, PROT_READ | PROT_WRITE,
                           MAP_PRIVATE | MAP_ANONYMOUS | MAP_HUGETLB, -1, 0);
                  if (p != (void *)ADDR_INPUT) {
                          perror("mmap");
                          break;
                  }
                  memset(p, 0, nr_hp * HPS);
                  munmap(p, nr_hp * HPS);
          }
  }

  $ sysctl vm.nr_hugepages=40
  $ ./hugepage 10 &
  $ ./movepages 10 $(pgrep -f hugepage)

Fixes: e632a938d914 ("mm: migrate: add hugepage migration code to move_pages()")
Signed-off-by: Naoya Horiguchi 
Reported-by: Hugh Dickins 
Cc: James Hogan 
Cc: David Rientjes 
Cc: Mel Gorman 
Cc: Johannes Weiner 
Cc: Michal Hocko 
Cc: Rik van Riel 
Cc: Andrea Arcangeli 
Cc: Luiz Capitulino 
Cc: Nishanth Aravamudan 
Cc: Lee Schermerhorn 
Cc: Steve Capper 
Cc: 	[3.12+]
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm: remove rest usage of VM_NONLINEAR and pte_file()

2015-02-10T22:30:31+00:00

One bit in ->vm_flags is unused now!

Signed-off-by: Kirill A. Shutemov 
Cc: Dan Carpenter 
Cc: Michal Hocko 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds