linux-stable.git/mm/memory.c, branch v4.19.166

mm: avoid data corruption on CoW fault into PFN-mapped VMA

2020-10-01T11:14:36+00:00

[ Upstream commit c3e5ea6ee574ae5e845a40ac8198de1fb63bb3ab ]

Jeff Moyer has reported that one of xfstests triggers a warning when run
on DAX-enabled filesystem:

	WARNING: CPU: 76 PID: 51024 at mm/memory.c:2317 wp_page_copy+0xc40/0xd50
	...
	wp_page_copy+0x98c/0xd50 (unreliable)
	do_wp_page+0xd8/0xad0
	__handle_mm_fault+0x748/0x1b90
	handle_mm_fault+0x120/0x1f0
	__do_page_fault+0x240/0xd70
	do_page_fault+0x38/0xd0
	handle_page_fault+0x10/0x30

The warning happens on failed __copy_from_user_inatomic() which tries to
copy data into a CoW page.

This happens because of race between MADV_DONTNEED and CoW page fault:

	CPU0					CPU1
 handle_mm_fault()
   do_wp_page()
     wp_page_copy()
       do_wp_page()
					madvise(MADV_DONTNEED)
					  zap_page_range()
					    zap_pte_range()
					      ptep_get_and_clear_full()
					      
	 __copy_from_user_inatomic()
	 sees empty PTE and fails
	 WARN_ON_ONCE(1)
	 clear_page()

The solution is to re-try __copy_from_user_inatomic() under PTL after
checking that PTE is matches the orig_pte.

The second copy attempt can still fail, like due to non-readable PTE, but
there's nothing reasonable we can do about, except clearing the CoW page.

Reported-by: Jeff Moyer 
Signed-off-by: Andrew Morton 
Signed-off-by: Kirill A. Shutemov 
Tested-by: Jeff Moyer 
Cc: 
Cc: Justin He 
Cc: Dan Williams 
Link: http://lkml.kernel.org/r/20200218154151.13349-1-kirill.shutemov@linux.intel.com
Signed-off-by: Linus Torvalds 
Signed-off-by: Sasha Levin

mm: fix double page fault on arm64 if PTE_AF is cleared

2020-10-01T11:14:24+00:00

[ Upstream commit 83d116c53058d505ddef051e90ab27f57015b025 ]

When we tested pmdk unit test [1] vmmalloc_fork TEST3 on arm64 guest, there
will be a double page fault in __copy_from_user_inatomic of cow_user_page.

To reproduce the bug, the cmd is as follows after you deployed everything:
make -C src/test/vmmalloc_fork/ TEST_TIME=60m check

Below call trace is from arm64 do_page_fault for debugging purpose:
[  110.016195] Call trace:
[  110.016826]  do_page_fault+0x5a4/0x690
[  110.017812]  do_mem_abort+0x50/0xb0
[  110.018726]  el1_da+0x20/0xc4
[  110.019492]  __arch_copy_from_user+0x180/0x280
[  110.020646]  do_wp_page+0xb0/0x860
[  110.021517]  __handle_mm_fault+0x994/0x1338
[  110.022606]  handle_mm_fault+0xe8/0x180
[  110.023584]  do_page_fault+0x240/0x690
[  110.024535]  do_mem_abort+0x50/0xb0
[  110.025423]  el0_da+0x20/0x24

The pte info before __copy_from_user_inatomic is (PTE_AF is cleared):
[ffff9b007000] pgd=000000023d4f8003, pud=000000023da9b003,
               pmd=000000023d4b3003, pte=360000298607bd3

As told by Catalin: "On arm64 without hardware Access Flag, copying from
user will fail because the pte is old and cannot be marked young. So we
always end up with zeroed page after fork() + CoW for pfn mappings. we
don't always have a hardware-managed access flag on arm64."

This patch fixes it by calling pte_mkyoung. Also, the parameter is
changed because vmf should be passed to cow_user_page()

Add a WARN_ON_ONCE when __copy_from_user_inatomic() returns error
in case there can be some obscure use-case (by Kirill).

[1] https://github.com/pmem/pmdk/tree/master/src/test/vmmalloc_fork

Signed-off-by: Jia He 
Reported-by: Yibo Cai 
Reviewed-by: Catalin Marinas 
Acked-by: Kirill A. Shutemov 
Signed-off-by: Catalin Marinas 
Signed-off-by: Sasha Levin

mm, thp, proc: report THP eligibility for each vma

2019-12-17T19:35:45+00:00

[ Upstream commit 7635d9cbe8327e131a1d3d8517dc186c2796ce2e ]

Userspace falls short when trying to find out whether a specific memory
range is eligible for THP.  There are usecases that would like to know
that
http://lkml.kernel.org/r/alpine.DEB.2.21.1809251248450.50347@chino.kir.corp.google.com
: This is used to identify heap mappings that should be able to fault thp
: but do not, and they normally point to a low-on-memory or fragmentation
: issue.

The only way to deduce this now is to query for hg resp.  nh flags and
confronting the state with the global setting.  Except that there is also
PR_SET_THP_DISABLE that might change the picture.  So the final logic is
not trivial.  Moreover the eligibility of the vma depends on the type of
VMA as well.  In the past we have supported only anononymous memory VMAs
but things have changed and shmem based vmas are supported as well these
days and the query logic gets even more complicated because the
eligibility depends on the mount option and another global configuration
knob.

Simplify the current state and report the THP eligibility in
/proc//smaps for each existing vma.  Reuse
transparent_hugepage_enabled for this purpose.  The original
implementation of this function assumes that the caller knows that the vma
itself is supported for THP so make the core checks into
__transparent_hugepage_enabled and use it for existing callers.
__show_smap just use the new transparent_hugepage_enabled which also
checks the vma support status (please note that this one has to be out of
line due to include dependency issues).

[mhocko@kernel.org: fix oops with NULL ->f_mapping]
  Link: http://lkml.kernel.org/r/20181224185106.GC16738@dhcp22.suse.cz
Link: http://lkml.kernel.org/r/20181211143641.3503-3-mhocko@kernel.org
Signed-off-by: Michal Hocko 
Acked-by: Vlastimil Babka 
Cc: Dan Williams 
Cc: David Rientjes 
Cc: Jan Kara 
Cc: Mike Rapoport 
Cc: Paul Oppenheimer 
Cc: William Kucharski 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds 
Signed-off-by: Sasha Levin

mm: use down_read_killable for locking mmap_sem in access_remote_vm

2019-07-31T05:27:09+00:00

[ Upstream commit 1e426fe28261b03f297992e89da3320b42816f4e ]

This function is used by ptrace and proc files like /proc/pid/cmdline and
/proc/pid/environ.

Access_remote_vm never returns error codes, all errors are ignored and
only size of successfully read data is returned.  So, if current task was
killed we'll simply return 0 (bytes read).

Mmap_sem could be locked for a long time or forever if something goes
wrong.  Using a killable lock permits cleanup of stuck tasks and
simplifies investigation.

Link: http://lkml.kernel.org/r/156007494202.3335.16782303099589302087.stgit@buzz
Signed-off-by: Konstantin Khlebnikov 
Reviewed-by: Michal Koutný 
Acked-by: Oleg Nesterov 
Acked-by: Michal Hocko 
Cc: Alexey Dobriyan 
Cc: Matthew Wilcox 
Cc: Cyrill Gorcunov 
Cc: Kirill Tkhai 
Cc: Al Viro 
Cc: Roman Gushchin 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds 
Signed-off-by: Sasha Levin

mm/memory.c: fix modifying of page protection by insert_pfn()

2019-05-16T17:41:26+00:00

[ Upstream commit cae85cb8add35f678cf487139d05e083ce2f570a ]

Aneesh has reported that PPC triggers the following warning when
excercising DAX code:

  IP set_pte_at+0x3c/0x190
  LR insert_pfn+0x208/0x280
  Call Trace:
     insert_pfn+0x68/0x280
     dax_iomap_pte_fault.isra.7+0x734/0xa40
     __xfs_filemap_fault+0x280/0x2d0
     do_wp_page+0x48c/0xa40
     __handle_mm_fault+0x8d0/0x1fd0
     handle_mm_fault+0x140/0x250
     __do_page_fault+0x300/0xd60
     handle_page_fault+0x18

Now that is WARN_ON in set_pte_at which is

        VM_WARN_ON(pte_hw_valid(*ptep) && !pte_protnone(*ptep));

The problem is that on some architectures set_pte_at() cannot cope with
a situation where there is already some (different) valid entry present.

Use ptep_set_access_flags() instead to modify the pfn which is built to
deal with modifying existing PTE.

Link: http://lkml.kernel.org/r/20190311084537.16029-1-jack@suse.cz
Fixes: b2770da64254 "mm: add vm_insert_mixed_mkwrite()"
Signed-off-by: Jan Kara 
Reported-by: "Aneesh Kumar K.V" 
Reviewed-by: Aneesh Kumar K.V 
Acked-by: Dan Williams 
Cc: Chandan Rajendra 
Cc: 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds 
Signed-off-by: Sasha Levin

mm: Fix warning in insert_pfn()

2019-05-02T07:58:59+00:00

commit f2c57d91b0d96aa13ccff4e3b178038f17b00658 upstream.

In DAX mode a write pagefault can race with write(2) in the following
way:

CPU0                            CPU1
                                write fault for mapped zero page (hole)
dax_iomap_rw()
  iomap_apply()
    xfs_file_iomap_begin()
      - allocates blocks
    dax_iomap_actor()
      invalidate_inode_pages2_range()
        - invalidates radix tree entries in given range
                                dax_iomap_pte_fault()
                                  grab_mapping_entry()
                                    - no entry found, creates empty
                                  ...
                                  xfs_file_iomap_begin()
                                    - finds already allocated block
                                  ...
                                  vmf_insert_mixed_mkwrite()
                                    - WARNs and does nothing because there
                                      is still zero page mapped in PTE
        unmap_mapping_pages()

This race results in WARN_ON from insert_pfn() and is occasionally
triggered by fstest generic/344. Note that the race is otherwise
harmless as before write(2) on CPU0 is finished, we will invalidate page
tables properly and thus user of mmap will see modified data from
write(2) from that point on. So just restrict the warning only to the
case when the PFN in PTE is not zero page.

Link: http://lkml.kernel.org/r/20180824154542.26872-1-jack@suse.cz
Signed-off-by: Jan Kara 
Reviewed-by: Andrew Morton 
Cc: Ross Zwisler 
Cc: Dan Williams 
Cc: Dave Jiang 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds 
Signed-off-by: Greg Kroah-Hartman

mm/memory.c: do_fault: avoid usage of stale vm_area_struct

2019-03-23T19:10:04+00:00

commit fc8efd2ddfed3f343c11b693e87140ff358d7ff5 upstream.

LTP testcase mtest06 [1] can trigger a crash on s390x running 5.0.0-rc8.
This is a stress test, where one thread mmaps/writes/munmaps memory area
and other thread is trying to read from it:

  CPU: 0 PID: 2611 Comm: mmap1 Not tainted 5.0.0-rc8+ #51
  Hardware name: IBM 2964 N63 400 (z/VM 6.4.0)
  Krnl PSW : 0404e00180000000 00000000001ac8d8 (__lock_acquire+0x7/0x7a8)
  Call Trace:
  ([<0000000000000000>]           (null))
   [<00000000001adae4>] lock_acquire+0xec/0x258
   [<000000000080d1ac>] _raw_spin_lock_bh+0x5c/0x98
   [<000000000012a780>] page_table_free+0x48/0x1a8
   [<00000000002f6e54>] do_fault+0xdc/0x670
   [<00000000002fadae>] __handle_mm_fault+0x416/0x5f0
   [<00000000002fb138>] handle_mm_fault+0x1b0/0x320
   [<00000000001248cc>] do_dat_exception+0x19c/0x2c8
   [<000000000080e5ee>] pgm_check_handler+0x19e/0x200

page_table_free() is called with NULL mm parameter, but because "0" is a
valid address on s390 (see S390_lowcore), it keeps going until it
eventually crashes in lockdep's lock_acquire.  This crash is
reproducible at least since 4.14.

Problem is that "vmf->vma" used in do_fault() can become stale.  Because
mmap_sem may be released, other threads can come in, call munmap() and
cause "vma" be returned to kmem cache, and get zeroed/re-initialized and
re-used:

handle_mm_fault                           |
  __handle_mm_fault                       |
    do_fault                              |
      vma = vmf->vma                      |
      do_read_fault                       |
        __do_fault                        |
          vma->vm_ops->fault(vmf);        |
            mmap_sem is released          |
                                          |
                                          | do_munmap()
                                          |   remove_vma_list()
                                          |     remove_vma()
                                          |       vm_area_free()
                                          |         # vma is released
                                          | ...
                                          | # same vma is allocated
                                          | # from kmem cache
                                          | do_mmap()
                                          |   vm_area_alloc()
                                          |     memset(vma, 0, ...)
                                          |
      pte_free(vma->vm_mm, ...);          |
        page_table_free                   |
          spin_lock_bh(&mm->context.lock);|
                                   |

Cache mm_struct to avoid using potentially stale "vma".

[1] https://github.com/linux-test-project/ltp/blob/master/testcases/kernel/mem/mtest06/mmap1.c

Link: http://lkml.kernel.org/r/5b3fdf19e2a5be460a384b936f5b56e13733f1b8.1551595137.git.jstancek@redhat.com
Signed-off-by: Jan Stancek 
Reviewed-by: Andrea Arcangeli 
Reviewed-by: Matthew Wilcox 
Acked-by: Rafael Aquini 
Reviewed-by: Minchan Kim 
Acked-by: Kirill A. Shutemov 
Cc: Rik van Riel 
Cc: Michal Hocko 
Cc: Huang Ying 
Cc: Souptick Joarder 
Cc: Jerome Glisse 
Cc: Aneesh Kumar K.V 
Cc: David Hildenbrand 
Cc: Andrea Arcangeli 
Cc: David Rientjes 
Cc: Mel Gorman 
Cc: 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds 
Signed-off-by: Greg Kroah-Hartman

mm, memcg: fix reclaim deadlock with writeback

2019-01-16T21:04:33+00:00

commit 63f3655f950186752236bb88a22f8252c11ce394 upstream.

Liu Bo has experienced a deadlock between memcg (legacy) reclaim and the
ext4 writeback

  task1:
    wait_on_page_bit+0x82/0xa0
    shrink_page_list+0x907/0x960
    shrink_inactive_list+0x2c7/0x680
    shrink_node_memcg+0x404/0x830
    shrink_node+0xd8/0x300
    do_try_to_free_pages+0x10d/0x330
    try_to_free_mem_cgroup_pages+0xd5/0x1b0
    try_charge+0x14d/0x720
    memcg_kmem_charge_memcg+0x3c/0xa0
    memcg_kmem_charge+0x7e/0xd0
    __alloc_pages_nodemask+0x178/0x260
    alloc_pages_current+0x95/0x140
    pte_alloc_one+0x17/0x40
    __pte_alloc+0x1e/0x110
    alloc_set_pte+0x5fe/0xc20
    do_fault+0x103/0x970
    handle_mm_fault+0x61e/0xd10
    __do_page_fault+0x252/0x4d0
    do_page_fault+0x30/0x80
    page_fault+0x28/0x30

  task2:
    __lock_page+0x86/0xa0
    mpage_prepare_extent_to_map+0x2e7/0x310 [ext4]
    ext4_writepages+0x479/0xd60
    do_writepages+0x1e/0x30
    __writeback_single_inode+0x45/0x320
    writeback_sb_inodes+0x272/0x600
    __writeback_inodes_wb+0x92/0xc0
    wb_writeback+0x268/0x300
    wb_workfn+0xb4/0x390
    process_one_work+0x189/0x420
    worker_thread+0x4e/0x4b0
    kthread+0xe6/0x100
    ret_from_fork+0x41/0x50

He adds
 "task1 is waiting for the PageWriteback bit of the page that task2 has
  collected in mpd->io_submit->io_bio, and tasks2 is waiting for the
  LOCKED bit the page which tasks1 has locked"

More precisely task1 is handling a page fault and it has a page locked
while it charges a new page table to a memcg.  That in turn hits a
memory limit reclaim and the memcg reclaim for legacy controller is
waiting on the writeback but that is never going to finish because the
writeback itself is waiting for the page locked in the #PF path.  So
this is essentially ABBA deadlock:

                                        lock_page(A)
                                        SetPageWriteback(A)
                                        unlock_page(A)
  lock_page(B)
                                        lock_page(B)
  pte_alloc_pne
    shrink_page_list
      wait_on_page_writeback(A)
                                        SetPageWriteback(B)
                                        unlock_page(B)

                                        # flush A, B to clear the writeback

This accumulating of more pages to flush is used by several filesystems
to generate a more optimal IO patterns.

Waiting for the writeback in legacy memcg controller is a workaround for
pre-mature OOM killer invocations because there is no dirty IO
throttling available for the controller.  There is no easy way around
that unfortunately.  Therefore fix this specific issue by pre-allocating
the page table outside of the page lock.  We have that handy
infrastructure for that already so simply reuse the fault-around pattern
which already does this.

There are probably other hidden __GFP_ACCOUNT | GFP_KERNEL allocations
from under a fs page locked but they should be really rare.  I am not
aware of a better solution unfortunately.

[akpm@linux-foundation.org: fix mm/memory.c:__do_fault()]
[akpm@linux-foundation.org: coding-style fixes]
[mhocko@kernel.org: enhance comment, per Johannes]
  Link: http://lkml.kernel.org/r/20181214084948.GA5624@dhcp22.suse.cz
Link: http://lkml.kernel.org/r/20181213092221.27270-1-mhocko@kernel.org
Fixes: c3b94f44fcb0 ("memcg: further prevent OOM with too many dirty pages")
Signed-off-by: Michal Hocko 
Reported-by: Liu Bo 
Debugged-by: Liu Bo 
Acked-by: Kirill A. Shutemov 
Acked-by: Johannes Weiner 
Reviewed-by: Liu Bo 
Cc: Jan Kara 
Cc: Dave Chinner 
Cc: Theodore Ts'o 
Cc: Vladimir Davydov 
Cc: Shakeel Butt 
Cc: 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds 
Signed-off-by: Greg Kroah-Hartman

mm/memory.c: recheck page table entry with page table lock held

2018-12-01T08:37:28+00:00

commit ff09d7ec9786be4ad7589aa987d7dc66e2dd9160 upstream.

We clear the pte temporarily during read/modify/write update of the pte.
If we take a page fault while the pte is cleared, the application can get
SIGBUS.  One such case is with remap_pfn_range without a backing
vm_ops->fault callback.  do_fault will return SIGBUS in that case.

cpu 0		 				cpu1
mprotect()
ptep_modify_prot_start()/pte cleared.
.
.						page fault.
.
.
prep_modify_prot_commit()

Fix this by taking page table lock and rechecking for pte_none.

[aneesh.kumar@linux.ibm.com: fix crash observed with syzkaller run]
  Link: http://lkml.kernel.org/r/87va6bwlfg.fsf@linux.ibm.com
Link: http://lkml.kernel.org/r/20180926031858.9692-1-aneesh.kumar@linux.ibm.com
Signed-off-by: Aneesh Kumar K.V 
Acked-by: Kirill A. Shutemov 
Cc: Willem de Bruijn 
Cc: Eric Dumazet 
Cc: Ido Schimmel 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds 
Signed-off-by: Greg Kroah-Hartman

mm/cow: don't bother write protecting already write-protected pages

2018-08-25T20:15:03+00:00

This is not normally noticeable, but repeated forks are unnecessarily
expensive because they repeatedly dirty the parent page tables during
the page table copy operation.

It's trivial to just avoid write protecting the page table entry if it
was already not writable.

This patch was inspired by

    https://bugzilla.kernel.org/show_bug.cgi?id=200447

which points to an ancient "waste time re-doing fork" issue in the
presence of lots of signals.

That bug was fixed by Eric Biederman's signal handling series
culminating in commit c3ad2c3b02e9 ("signal: Don't restart fork when
signals come in"), but the unnecessary work for repeated forks is still
work just fixing, particularly since the fix is trivial.

Cc: Eric Biederman 
Cc: Oleg Nesterov 
Cc: Andrew Morton 
Signed-off-by: Linus Torvalds