[LTP] [PATCH v17 0/2] futex: Add EFAULT error coverage tests

[Michael Menasherov]

Hi Petr,

Thanks for the review. Here is v17 addressing your feedback.

futex_wait06 and futex_wait07 were already merged. This series contains
the remaining two patches.

futex_cmp_requeue03:
  Applied your nit — removed the exp_errno field from the testcase struct
  and used EFAULT directly in TST_EXP_FAIL().

futex_wake05:
  Applied both nits (list comment format, EFAULT directly). For the
  kernel-space address case: you were right to question it. I couldn't
  confirm consistent EFAULT across kernels, so I looked for a better
  replacement.

  I used AI assistance to research the kernel's get_user_pages() code
  paths and cross-referenced existing LTP mmap tests to verify the
  approach. The replacement I landed on is a shared file-backed mapping
  where the file is truncated to 0 after mmap().

  The three cases now exercise genuinely different code paths:

  - unmapped memory fails at find_vma() (no VMA exists)
  - PROT_NONE memory fails at get_user_pages_fast() (VMA exists but
    page is inaccessible)
  - the truncated file mapping triggers VM_FAULT_SIGBUS inside the page
    fault handler (filemap_fault() sees offset beyond EOF), which
    get_user_pages() propagates as EFAULT

  The SIGBUS is never delivered to user space — get_user_pages() converts
  VM_FAULT_SIGBUS to -EFAULT internally. This behavior has been stable
  since before kernel 2.6 and works reliably on all architectures and
  both 32/64-bit. The test uses .needs_tmpdir = 1.

Changes since v16:
- futex_wake05: replace kernel-space address case with truncated
  file-backed mapping, fix comment to list format, use EFAULT directly
  in TST_EXP_FAIL(), add .needs_tmpdir
- futex_cmp_requeue03: use EFAULT directly in TST_EXP_FAIL()

Michael Menasherov (2):
  futex_wake05: Add EFAULT error coverage test
  futex_cmp_requeue03: Add EFAULT error coverage test

 runtest/syscalls                              |   2 +
 testcases/kernel/syscalls/futex/.gitignore    |   2 +
 .../syscalls/futex/futex_cmp_requeue03.c      | 103 ++++++++++++++++
 .../kernel/syscalls/futex/futex_wake05.c      | 113 ++++++++++++++++++
 4 files changed, 220 insertions(+)
 create mode 100644 testcases/kernel/syscalls/futex/futex_cmp_requeue03.c
 create mode 100644 testcases/kernel/syscalls/futex/futex_wake05.c

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2.55.0