linux.git/mm/memory.c, branch v4.13

dax: update to new mmu_notifier semantic

2017-08-31T23:12:59+00:00

Replace all mmu_notifier_invalidate_page() calls by *_invalidate_range()
and make sure it is bracketed by calls to *_invalidate_range_start()/end().

Note that because we can not presume the pmd value or pte value we have
to assume the worst and unconditionaly report an invalidation as
happening.

Signed-off-by: Jérôme Glisse 
Cc: Dan Williams 
Cc: Ross Zwisler 
Cc: Bernhard Held 
Cc: Adam Borowski 
Cc: Andrea Arcangeli 
Cc: Radim Krčmář 
Cc: Wanpeng Li 
Cc: Paolo Bonzini 
Cc: Takashi Iwai 
Cc: Nadav Amit 
Cc: Mike Galbraith 
Cc: Kirill A. Shutemov 
Cc: axie 
Cc: Andrew Morton 
Signed-off-by: Linus Torvalds

mm, oom: fix potential data corruption when oom_reaper races with writer

2017-08-18T22:32:01+00:00

Wenwei Tao has noticed that our current assumption that the oom victim
is dying and never doing any visible changes after it dies, and so the
oom_reaper can tear it down, is not entirely true.

__task_will_free_mem consider a task dying when SIGNAL_GROUP_EXIT is set
but do_group_exit sends SIGKILL to all threads _after_ the flag is set.
So there is a race window when some threads won't have
fatal_signal_pending while the oom_reaper could start unmapping the
address space.  Moreover some paths might not check for fatal signals
before each PF/g-u-p/copy_from_user.

We already have a protection for oom_reaper vs.  PF races by checking
MMF_UNSTABLE.  This has been, however, checked only for kernel threads
(use_mm users) which can outlive the oom victim.  A simple fix would be
to extend the current check in handle_mm_fault for all tasks but that
wouldn't be sufficient because the current check assumes that a kernel
thread would bail out after EFAULT from get_user*/copy_from_user and
never re-read the same address which would succeed because the PF path
has established page tables already.  This seems to be the case for the
only existing use_mm user currently (virtio driver) but it is rather
fragile in general.

This is even more fragile in general for more complex paths such as
generic_perform_write which can re-read the same address more times
(e.g.  iov_iter_copy_from_user_atomic to fail and then
iov_iter_fault_in_readable on retry).

Therefore we have to implement MMF_UNSTABLE protection in a robust way
and never make a potentially corrupted content visible.  That requires
to hook deeper into the PF path and check for the flag _every time_
before a pte for anonymous memory is established (that means all
!VM_SHARED mappings).

The corruption can be triggered artificially
(http://lkml.kernel.org/r/201708040646.v746kkhC024636@www262.sakura.ne.jp)
but there doesn't seem to be any real life bug report.  The race window
should be quite tight to trigger most of the time.

Link: http://lkml.kernel.org/r/20170807113839.16695-3-mhocko@kernel.org
Fixes: aac453635549 ("mm, oom: introduce oom reaper")
Signed-off-by: Michal Hocko 
Reported-by: Wenwei Tao 
Tested-by: Tetsuo Handa 
Cc: "Kirill A. Shutemov" 
Cc: Andrea Argangeli 
Cc: David Rientjes 
Cc: Oleg Nesterov 
Cc: Tetsuo Handa 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm: fix double mmap_sem unlock on MMF_UNSTABLE enforced SIGBUS

2017-08-18T22:32:01+00:00

Tetsuo Handa has noticed that MMF_UNSTABLE SIGBUS path in
handle_mm_fault causes a lockdep splat

  Out of memory: Kill process 1056 (a.out) score 603 or sacrifice child
  Killed process 1056 (a.out) total-vm:4268108kB, anon-rss:2246048kB, file-rss:0kB, shmem-rss:0kB
  a.out (1169) used greatest stack depth: 11664 bytes left
  DEBUG_LOCKS_WARN_ON(depth <= 0)
  ------------[ cut here ]------------
  WARNING: CPU: 6 PID: 1339 at kernel/locking/lockdep.c:3617 lock_release+0x172/0x1e0
  CPU: 6 PID: 1339 Comm: a.out Not tainted 4.13.0-rc3-next-20170803+ #142
  Hardware name: VMware, Inc. VMware Virtual Platform/440BX Desktop Reference Platform, BIOS 6.00 07/02/2015
  RIP: 0010:lock_release+0x172/0x1e0
  Call Trace:
     up_read+0x1a/0x40
     __do_page_fault+0x28e/0x4c0
     do_page_fault+0x30/0x80
     page_fault+0x28/0x30

The reason is that the page fault path might have dropped the mmap_sem
and returned with VM_FAULT_RETRY.  MMF_UNSTABLE check however rewrites
the error path to VM_FAULT_SIGBUS and we always expect mmap_sem taken in
that path.  Fix this by taking mmap_sem when VM_FAULT_RETRY is held in
the MMF_UNSTABLE path.

We cannot simply add VM_FAULT_SIGBUS to the existing error code because
all arch specific page fault handlers and g-u-p would have to learn a
new error code combination.

Link: http://lkml.kernel.org/r/20170807113839.16695-2-mhocko@kernel.org
Fixes: 3f70dc38cec2 ("mm: make sure that kthreads will not refault oom reaped memory")
Reported-by: Tetsuo Handa 
Signed-off-by: Michal Hocko 
Acked-by: David Rientjes 
Cc: Andrea Argangeli 
Cc: "Kirill A. Shutemov" 
Cc: Oleg Nesterov 
Cc: Wenwei Tao 
Cc: 	[4.9+]
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm: fix MADV_[FREE|DONTNEED] TLB flush miss problem

2017-08-10T22:54:07+00:00

Nadav reported parallel MADV_DONTNEED on same range has a stale TLB
problem and Mel fixed it[1] and found same problem on MADV_FREE[2].

Quote from Mel Gorman:
 "The race in question is CPU 0 running madv_free and updating some PTEs
  while CPU 1 is also running madv_free and looking at the same PTEs.
  CPU 1 may have writable TLB entries for a page but fail the pte_dirty
  check (because CPU 0 has updated it already) and potentially fail to
  flush.

  Hence, when madv_free on CPU 1 returns, there are still potentially
  writable TLB entries and the underlying PTE is still present so that a
  subsequent write does not necessarily propagate the dirty bit to the
  underlying PTE any more. Reclaim at some unknown time at the future
  may then see that the PTE is still clean and discard the page even
  though a write has happened in the meantime. I think this is possible
  but I could have missed some protection in madv_free that prevents it
  happening."

This patch aims for solving both problems all at once and is ready for
other problem with KSM, MADV_FREE and soft-dirty story[3].

TLB batch API(tlb_[gather|finish]_mmu] uses [inc|dec]_tlb_flush_pending
and mmu_tlb_flush_pending so that when tlb_finish_mmu is called, we can
catch there are parallel threads going on.  In that case, forcefully,
flush TLB to prevent for user to access memory via stale TLB entry
although it fail to gather page table entry.

I confirmed this patch works with [4] test program Nadav gave so this
patch supersedes "mm: Always flush VMA ranges affected by zap_page_range
v2" in current mmotm.

NOTE:

This patch modifies arch-specific TLB gathering interface(x86, ia64,
s390, sh, um).  It seems most of architecture are straightforward but
s390 need to be careful because tlb_flush_mmu works only if
mm->context.flush_mm is set to non-zero which happens only a pte entry
really is cleared by ptep_get_and_clear and friends.  However, this
problem never changes the pte entries but need to flush to prevent
memory access from stale tlb.

[1] http://lkml.kernel.org/r/20170725101230.5v7gvnjmcnkzzql3@techsingularity.net
[2] http://lkml.kernel.org/r/20170725100722.2dxnmgypmwnrfawp@suse.de
[3] http://lkml.kernel.org/r/BD3A0EBE-ECF4-41D4-87FA-C755EA9AB6BD@gmail.com
[4] https://patchwork.kernel.org/patch/9861621/

[minchan@kernel.org: decrease tlb flush pending count in tlb_finish_mmu]
  Link: http://lkml.kernel.org/r/20170808080821.GA31730@bbox
Link: http://lkml.kernel.org/r/20170802000818.4760-7-namit@vmware.com
Signed-off-by: Minchan Kim 
Signed-off-by: Nadav Amit 
Reported-by: Nadav Amit 
Reported-by: Mel Gorman 
Acked-by: Mel Gorman 
Cc: Ingo Molnar 
Cc: Russell King 
Cc: Tony Luck 
Cc: Martin Schwidefsky 
Cc: "David S. Miller" 
Cc: Heiko Carstens 
Cc: Yoshinori Sato 
Cc: Jeff Dike 
Cc: Andrea Arcangeli 
Cc: Andy Lutomirski 
Cc: Hugh Dickins 
Cc: Mel Gorman 
Cc: Nadav Amit 
Cc: Rik van Riel 
Cc: Sergey Senozhatsky 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm: refactor TLB gathering API

2017-08-10T22:54:07+00:00

This patch is a preparatory patch for solving race problems caused by
TLB batch.  For that, we will increase/decrease TLB flush pending count
of mm_struct whenever tlb_[gather|finish]_mmu is called.

Before making it simple, this patch separates architecture specific part
and rename it to arch_tlb_[gather|finish]_mmu and generic part just
calls it.

It shouldn't change any behavior.

Link: http://lkml.kernel.org/r/20170802000818.4760-5-namit@vmware.com
Signed-off-by: Minchan Kim 
Signed-off-by: Nadav Amit 
Acked-by: Mel Gorman 
Cc: Ingo Molnar 
Cc: Russell King 
Cc: Tony Luck 
Cc: Martin Schwidefsky 
Cc: "David S. Miller" 
Cc: Heiko Carstens 
Cc: Yoshinori Sato 
Cc: Jeff Dike 
Cc: Andrea Arcangeli 
Cc: Andy Lutomirski 
Cc: Hugh Dickins 
Cc: Mel Gorman 
Cc: Nadav Amit 
Cc: Rik van Riel 
Cc: Sergey Senozhatsky 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm, mprotect: flush TLB if potentially racing with a parallel reclaim leaving stale TLB entries

2017-08-02T23:34:46+00:00

Nadav Amit identified a theoritical race between page reclaim and
mprotect due to TLB flushes being batched outside of the PTL being held.

He described the race as follows:

        CPU0                            CPU1
        ----                            ----
                                        user accesses memory using RW PTE
                                        [PTE now cached in TLB]
        try_to_unmap_one()
        ==> ptep_get_and_clear()
        ==> set_tlb_ubc_flush_pending()
                                        mprotect(addr, PROT_READ)
                                        ==> change_pte_range()
                                        ==> [ PTE non-present - no flush ]

                                        user writes using cached RW PTE
        ...

        try_to_unmap_flush()

The same type of race exists for reads when protecting for PROT_NONE and
also exists for operations that can leave an old TLB entry behind such
as munmap, mremap and madvise.

For some operations like mprotect, it's not necessarily a data integrity
issue but it is a correctness issue as there is a window where an
mprotect that limits access still allows access.  For munmap, it's
potentially a data integrity issue although the race is massive as an
munmap, mmap and return to userspace must all complete between the
window when reclaim drops the PTL and flushes the TLB.  However, it's
theoritically possible so handle this issue by flushing the mm if
reclaim is potentially currently batching TLB flushes.

Other instances where a flush is required for a present pte should be ok
as either the page lock is held preventing parallel reclaim or a page
reference count is elevated preventing a parallel free leading to
corruption.  In the case of page_mkclean there isn't an obvious path
that userspace could take advantage of without using the operations that
are guarded by this patch.  Other users such as gup as a race with
reclaim looks just at PTEs.  huge page variants should be ok as they
don't race with reclaim.  mincore only looks at PTEs.  userfault also
should be ok as if a parallel reclaim takes place, it will either fault
the page back in or read some of the data before the flush occurs
triggering a fault.

Note that a variant of this patch was acked by Andy Lutomirski but this
was for the x86 parts on top of his PCID work which didn't make the 4.13
merge window as expected.  His ack is dropped from this version and
there will be a follow-on patch on top of PCID that will include his
ack.

[akpm@linux-foundation.org: tweak comments]
[akpm@linux-foundation.org: fix spello]
Link: http://lkml.kernel.org/r/20170717155523.emckq2esjro6hf3z@suse.de
Reported-by: Nadav Amit 
Signed-off-by: Mel Gorman 
Cc: Andy Lutomirski 
Cc: 	[v4.4+]
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm/memory.c: mark create_huge_pmd() inline to prevent build failure

2017-07-12T23:25:59+00:00

With gcc 4.1.2:

    mm/memory.o: In function `create_huge_pmd':
    memory.c:(.text+0x93e): undefined reference to `do_huge_pmd_anonymous_page'

Interestingly, create_huge_pmd() is emitted in the assembler output, but
never called.

Converting transparent_hugepage_enabled() from a macro to a static
inline function reduced the ability of the compiler to remove unused
code.

Fix this by marking create_huge_pmd() inline.

Fixes: 16981d763501c0e0 ("mm: improve readability of transparent_hugepage_enabled()")
Link: http://lkml.kernel.org/r/1499842660-10665-1-git-send-email-geert@linux-m68k.org
Signed-off-by: Geert Uytterhoeven 
Acked-by: Arnd Bergmann 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm/memory.c: convert to DEFINE_DEBUGFS_ATTRIBUTE

2017-07-10T23:32:30+00:00

The preferred strategy to define debugfs attributes is to use the
DEFINE_DEBUGFS_ATTRIBUTE() macro and to use debugfs_create_file_unsafe().

Link: http://lkml.kernel.org/r/20170528145948.32127-1-y.pronenko@gmail.com
Signed-off-by: Yevgen Pronenko 
Cc: "Kirill A . Shutemov" 
Cc: Jan Kara 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm: per-cgroup memory reclaim stats

2017-07-06T23:24:35+00:00

Track the following reclaim counters for every memory cgroup: PGREFILL,
PGSCAN, PGSTEAL, PGACTIVATE, PGDEACTIVATE, PGLAZYFREE and PGLAZYFREED.

These values are exposed using the memory.stats interface of cgroup v2.

The meaning of each value is the same as for global counters, available
using /proc/vmstat.

Also, for consistency, rename mem_cgroup_count_vm_event() to
count_memcg_event_mm().

Link: http://lkml.kernel.org/r/1494530183-30808-1-git-send-email-guro@fb.com
Signed-off-by: Roman Gushchin 
Suggested-by: Johannes Weiner 
Acked-by: Michal Hocko 
Acked-by: Vladimir Davydov 
Acked-by: Johannes Weiner 
Cc: Tejun Heo 
Cc: Li Zefan 
Cc: Balbir Singh 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm: drop NULL return check of pte_offset_map_lock()

2017-07-06T23:24:33+00:00

pte_offset_map_lock() finds and takes ptl, and returns pte.  But some
callers return without unlocking the ptl when pte == NULL, which seems
weird.

Git history said that !pte check in change_pte_range() was introduced in
commit 1ad9f620c3a2 ("mm: numa: recheck for transhuge pages under lock
during protection changes") and still remains after commit 175ad4f1e7a2
("mm: mprotect: use pmd_trans_unstable instead of taking the pmd_lock")
which partially reverts 1ad9f620c3a2.  So I think that it's just dead
code.

Many other caller of pte_offset_map_lock() never check NULL return, so
let's do likewise.

Link: http://lkml.kernel.org/r/1495089737-1292-1-git-send-email-n-horiguchi@ah.jp.nec.com
Signed-off-by: Naoya Horiguchi 
Acked-by: Vlastimil Babka 
Cc: Mel Gorman 
Cc: Johannes Weiner 
Cc: Andrea Arcangeli 
Cc: Rik van Riel 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds