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  1. 13 1月, 2021 1 次提交
  3. 16 12月, 2020 8 次提交
  5. 15 11月, 2020 1 次提交
    • M
      hugetlbfs: fix anon huge page migration race · 336bf30e
      由 Mike Kravetz 提交于 
      Qian Cai reported the following BUG in [1]

  LTP: starting move_pages12
  BUG: unable to handle page fault for address: ffffffffffffffe0
  ...
  RIP: 0010:anon_vma_interval_tree_iter_first+0xa2/0x170 avc_start_pgoff at mm/interval_tree.c:63
  Call Trace:
    rmap_walk_anon+0x141/0xa30 rmap_walk_anon at mm/rmap.c:1864
    try_to_unmap+0x209/0x2d0 try_to_unmap at mm/rmap.c:1763
    migrate_pages+0x1005/0x1fb0
    move_pages_and_store_status.isra.47+0xd7/0x1a0
    __x64_sys_move_pages+0xa5c/0x1100
    do_syscall_64+0x5f/0x310
    entry_SYSCALL_64_after_hwframe+0x44/0xa9

Hugh Dickins diagnosed this as a migration bug caused by code introduced
to use i_mmap_rwsem for pmd sharing synchronization.  Specifically, the
routine unmap_and_move_huge_page() is always passing the TTU_RMAP_LOCKED
flag to try_to_unmap() while holding i_mmap_rwsem.  This is wrong for
anon pages as the anon_vma_lock should be held in this case.  Further
analysis suggested that i_mmap_rwsem was not required to he held at all
when calling try_to_unmap for anon pages as an anon page could never be
part of a shared pmd mapping.

Discussion also revealed that the hack in hugetlb_page_mapping_lock_write
to drop page lock and acquire i_mmap_rwsem is wrong.  There is no way to
keep mapping valid while dropping page lock.

This patch does the following:

 - Do not take i_mmap_rwsem and set TTU_RMAP_LOCKED for anon pages when
   calling try_to_unmap.

 - Remove the hacky code in hugetlb_page_mapping_lock_write. The routine
   will now simply do a 'trylock' while still holding the page lock. If
   the trylock fails, it will return NULL. This could impact the
   callers:

    - migration calling code will receive -EAGAIN and retry up to the
      hard coded limit (10).

    - memory error code will treat the page as BUSY. This will force
      killing (SIGKILL) instead of SIGBUS any mapping tasks.

   Do note that this change in behavior only happens when there is a
   race. None of the standard kernel testing suites actually hit this
   race, but it is possible.

[1] https://lore.kernel.org/lkml/20200708012044.GC992@lca.pw/
[2] https://lore.kernel.org/linux-mm/alpine.LSU.2.11.2010071833100.2214@eggly.anvils/

Fixes: c0d0381a ("hugetlbfs: use i_mmap_rwsem for more pmd sharing synchronization")
Reported-by: NQian Cai <cai@lca.pw>
Suggested-by: NHugh Dickins <hughd@google.com>
Signed-off-by: NMike Kravetz <mike.kravetz@oracle.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Acked-by: NNaoya Horiguchi <naoya.horiguchi@nec.com>
Cc: <stable@vger.kernel.org>
Link: https://lkml.kernel.org/r/20201105195058.78401-1-mike.kravetz@oracle.comSigned-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      336bf30e
  7. 19 10月, 2020 1 次提交
  9. 17 10月, 2020 12 次提交
  11. 14 10月, 2020 2 次提交
  13. 25 9月, 2020 1 次提交
  15. 13 8月, 2020 1 次提交
    • J
      mm/migrate: introduce a standard migration target allocation function · 19fc7bed
      由 Joonsoo Kim 提交于 
      There are some similar functions for migration target allocation.  Since
there is no fundamental difference, it's better to keep just one rather
than keeping all variants.  This patch implements base migration target
allocation function.  In the following patches, variants will be converted
to use this function.

Changes should be mechanical, but, unfortunately, there are some
differences.  First, some callers' nodemask is assgined to NULL since NULL
nodemask will be considered as all available nodes, that is,
&node_states[N_MEMORY].  Second, for hugetlb page allocation, gfp_mask is
redefined as regular hugetlb allocation gfp_mask plus __GFP_THISNODE if
user provided gfp_mask has it.  This is because future caller of this
function requires to set this node constaint.  Lastly, if provided nodeid
is NUMA_NO_NODE, nodeid is set up to the node where migration source
lives.  It helps to remove simple wrappers for setting up the nodeid.

Note that PageHighmem() call in previous function is changed to open-code
"is_highmem_idx()" since it provides more readability.

[akpm@linux-foundation.org: tweak patch title, per Vlastimil]
[akpm@linux-foundation.org: fix typo in comment]
Signed-off-by: NJoonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Acked-by: NVlastimil Babka <vbabka@suse.cz>
Acked-by: NMichal Hocko <mhocko@suse.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Roman Gushchin <guro@fb.com>
Link: http://lkml.kernel.org/r/1594622517-20681-6-git-send-email-iamjoonsoo.kim@lge.comSigned-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      19fc7bed
  17. 12 6月, 2020 2 次提交
  19. 03 6月, 2020 1 次提交
  21. 20 5月, 2020 1 次提交
  23. 08 4月, 2020 1 次提交
  25. 03 4月, 2020 1 次提交
    • M
      hugetlbfs: use i_mmap_rwsem for more pmd sharing synchronization · c0d0381a
      由 Mike Kravetz 提交于 
      Patch series "hugetlbfs: use i_mmap_rwsem for more synchronization", v2.

While discussing the issue with huge_pte_offset [1], I remembered that
there were more outstanding hugetlb races.  These issues are:

1) For shared pmds, huge PTE pointers returned by huge_pte_alloc can become
   invalid via a call to huge_pmd_unshare by another thread.
2) hugetlbfs page faults can race with truncation causing invalid global
   reserve counts and state.

A previous attempt was made to use i_mmap_rwsem in this manner as
described at [2].  However, those patches were reverted starting with [3]
due to locking issues.

To effectively use i_mmap_rwsem to address the above issues it needs to be
held (in read mode) during page fault processing.  However, during fault
processing we need to lock the page we will be adding.  Lock ordering
requires we take page lock before i_mmap_rwsem.  Waiting until after
taking the page lock is too late in the fault process for the
synchronization we want to do.

To address this lock ordering issue, the following patches change the lock
ordering for hugetlb pages.  This is not too invasive as hugetlbfs
processing is done separate from core mm in many places.  However, I don't
really like this idea.  Much ugliness is contained in the new routine
hugetlb_page_mapping_lock_write() of patch 1.

The only other way I can think of to address these issues is by catching
all the races.  After catching a race, cleanup, backout, retry ...  etc,
as needed.  This can get really ugly, especially for huge page
reservations.  At one time, I started writing some of the reservation
backout code for page faults and it got so ugly and complicated I went
down the path of adding synchronization to avoid the races.  Any other
suggestions would be welcome.

[1] https://lore.kernel.org/linux-mm/1582342427-230392-1-git-send-email-longpeng2@huawei.com/
[2] https://lore.kernel.org/linux-mm/20181222223013.22193-1-mike.kravetz@oracle.com/
[3] https://lore.kernel.org/linux-mm/20190103235452.29335-1-mike.kravetz@oracle.com
[4] https://lore.kernel.org/linux-mm/1584028670.7365.182.camel@lca.pw/
[5] https://lore.kernel.org/lkml/20200312183142.108df9ac@canb.auug.org.au/

This patch (of 2):

While looking at BUGs associated with invalid huge page map counts, it was
discovered and observed that a huge pte pointer could become 'invalid' and
point to another task's page table.  Consider the following:

A task takes a page fault on a shared hugetlbfs file and calls
huge_pte_alloc to get a ptep.  Suppose the returned ptep points to a
shared pmd.

Now, another task truncates the hugetlbfs file.  As part of truncation, it
unmaps everyone who has the file mapped.  If the range being truncated is
covered by a shared pmd, huge_pmd_unshare will be called.  For all but the
last user of the shared pmd, huge_pmd_unshare will clear the pud pointing
to the pmd.  If the task in the middle of the page fault is not the last
user, the ptep returned by huge_pte_alloc now points to another task's
page table or worse.  This leads to bad things such as incorrect page
map/reference counts or invalid memory references.

To fix, expand the use of i_mmap_rwsem as follows:
- i_mmap_rwsem is held in read mode whenever huge_pmd_share is called.
  huge_pmd_share is only called via huge_pte_alloc, so callers of
  huge_pte_alloc take i_mmap_rwsem before calling.  In addition, callers
  of huge_pte_alloc continue to hold the semaphore until finished with
  the ptep.
- i_mmap_rwsem is held in write mode whenever huge_pmd_unshare is called.

One problem with this scheme is that it requires taking i_mmap_rwsem
before taking the page lock during page faults.  This is not the order
specified in the rest of mm code.  Handling of hugetlbfs pages is mostly
isolated today.  Therefore, we use this alternative locking order for
PageHuge() pages.

         mapping->i_mmap_rwsem
           hugetlb_fault_mutex (hugetlbfs specific page fault mutex)
             page->flags PG_locked (lock_page)

To help with lock ordering issues, hugetlb_page_mapping_lock_write() is
introduced to write lock the i_mmap_rwsem associated with a page.

In most cases it is easy to get address_space via vma->vm_file->f_mapping.
However, in the case of migration or memory errors for anon pages we do
not have an associated vma.  A new routine _get_hugetlb_page_mapping()
will use anon_vma to get address_space in these cases.
Signed-off-by: NMike Kravetz <mike.kravetz@oracle.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: "Aneesh Kumar K . V" <aneesh.kumar@linux.vnet.ibm.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Prakash Sangappa <prakash.sangappa@oracle.com>
Link: http://lkml.kernel.org/r/20200316205756.146666-2-mike.kravetz@oracle.comSigned-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      c0d0381a
  27. 02 12月, 2019 3 次提交
  29. 19 10月, 2019 1 次提交
  31. 15 10月, 2019 1 次提交
    • J
      mm/memory-failure: poison read receives SIGKILL instead of SIGBUS if mmaped more than once · 3d7fed4a
      由 Jane Chu 提交于 
      Mmap /dev/dax more than once, then read the poison location using
address from one of the mappings.  The other mappings due to not having
the page mapped in will cause SIGKILLs delivered to the process.
SIGKILL succeeds over SIGBUS, so user process loses the opportunity to
handle the UE.

Although one may add MAP_POPULATE to mmap(2) to work around the issue,
MAP_POPULATE makes mapping 128GB of pmem several magnitudes slower, so
isn't always an option.

Details -

  ndctl inject-error --block=10 --count=1 namespace6.0

  ./read_poison -x dax6.0 -o 5120 -m 2
  mmaped address 0x7f5bb6600000
  mmaped address 0x7f3cf3600000
  doing local read at address 0x7f3cf3601400
  Killed

Console messages in instrumented kernel -

  mce: Uncorrected hardware memory error in user-access at edbe201400
  Memory failure: tk->addr = 7f5bb6601000
  Memory failure: address edbe201: call dev_pagemap_mapping_shift
  dev_pagemap_mapping_shift: page edbe201: no PUD
  Memory failure: tk->size_shift == 0
  Memory failure: Unable to find user space address edbe201 in read_poison
  Memory failure: tk->addr = 7f3cf3601000
  Memory failure: address edbe201: call dev_pagemap_mapping_shift
  Memory failure: tk->size_shift = 21
  Memory failure: 0xedbe201: forcibly killing read_poison:22434 because of failure to unmap corrupted page
    => to deliver SIGKILL
  Memory failure: 0xedbe201: Killing read_poison:22434 due to hardware memory corruption
    => to deliver SIGBUS

Link: http://lkml.kernel.org/r/1565112345-28754-3-git-send-email-jane.chu@oracle.comSigned-off-by: NJane Chu <jane.chu@oracle.com>
Suggested-by: NNaoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Reviewed-by: NDan Williams <dan.j.williams@intel.com>
Acked-by: NNaoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      3d7fed4a
  33. 13 7月, 2019 1 次提交
  35. 03 7月, 2019 1 次提交