Re: [kbuild-all] Re: [linux-next:master 5756/5946] mm/userfaultfd.c:212:6: warning: variable 'vm_alloc_shared' set but not used

[Rong Chen <rong.a.chen@xxxxxxxxx>]

On 6/2/21 4:18 PM, Souptick Joarder wrote:
> On Tue, Jun 1, 2021 at 5:40 PM kernel test robot <lkp@xxxxxxxxx> wrote:
> > tree:   https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git master
> > head:   392d24c0d06bc89a762ba66977db41e53c21bfb5
> > commit: 1786d001262006df52cdcda4cbc0c8087a0200ec [5756/5946] mm, hugetlb: fix racy resv_huge_pages underflow on UFFDIO_COPY
> > config: powerpc64-randconfig-r022-20210601 (attached as .config)
> > compiler: powerpc-linux-gcc (GCC) 9.3.0
> > reproduce (this is a W=1 build):
> >          wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
> >          chmod +x ~/bin/make.cross
> >          # https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/?id=1786d001262006df52cdcda4cbc0c8087a0200ec
> >          git remote add linux-next https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git
> >          git fetch --no-tags linux-next master
> >          git checkout 1786d001262006df52cdcda4cbc0c8087a0200ec
> >          # save the attached .config to linux build tree
> >          COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-9.3.0 make.cross ARCH=powerpc64
> >
> > If you fix the issue, kindly add following tag as appropriate
> > Reported-by: kernel test robot <lkp@xxxxxxxxx>
> >
> > All warnings (new ones prefixed by >>):
> >
> >     mm/userfaultfd.c: In function '__mcopy_atomic_hugetlb':
> > > > mm/userfaultfd.c:212:6: warning: variable 'vm_alloc_shared' set but not used [-Wunused-but-set-variable]
> >       212 |  int vm_alloc_shared = dst_vma->vm_flags & VM_SHARED;
> >           |      ^~~~~~~~~~~~~~~
> Looks like a false warning. vm_alloc_shared is set here within the
> same function.

Hi Souptick,

The warning is the same as you said,  vm_alloc_shared is only set but 
not used.

Best Regards,
Rong Chen

> mutex_unlock(&hugetlb_fault_mutex_table[hash]);
> i_mmap_unlock_read(mapping);
> vm_alloc_shared = vm_shared;
>
> > vim +/vm_alloc_shared +212 mm/userfaultfd.c
> >
> > c1a4de99fada21 Andrea Arcangeli  2015-09-04  199
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  200  #ifdef CONFIG_HUGETLB_PAGE
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  201  /*
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  202   * __mcopy_atomic processing for HUGETLB vmas.  Note that this routine is
> > c1e8d7c6a7a682 Michel Lespinasse 2020-06-08  203   * called with mmap_lock held, it will release mmap_lock before returning.
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  204   */
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  205  static __always_inline ssize_t __mcopy_atomic_hugetlb(struct mm_struct *dst_mm,
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  206                                              struct vm_area_struct *dst_vma,
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  207                                              unsigned long dst_start,
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  208                                              unsigned long src_start,
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  209                                              unsigned long len,
> > f619147104c8ea Axel Rasmussen    2021-05-04  210                                              enum mcopy_atomic_mode mode)
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  211  {
> > 1c9e8def43a345 Mike Kravetz      2017-02-22 @212        int vm_alloc_shared = dst_vma->vm_flags & VM_SHARED;
> > 1c9e8def43a345 Mike Kravetz      2017-02-22  213        int vm_shared = dst_vma->vm_flags & VM_SHARED;
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  214        ssize_t err;
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  215        pte_t *dst_pte;
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  216        unsigned long src_addr, dst_addr;
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  217        long copied;
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  218        struct page *page;
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  219        unsigned long vma_hpagesize;
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  220        pgoff_t idx;
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  221        u32 hash;
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  222        struct address_space *mapping;
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  223
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  224        /*
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  225         * There is no default zero huge page for all huge page sizes as
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  226         * supported by hugetlb.  A PMD_SIZE huge pages may exist as used
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  227         * by THP.  Since we can not reliably insert a zero page, this
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  228         * feature is not supported.
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  229         */
> > f619147104c8ea Axel Rasmussen    2021-05-04  230        if (mode == MCOPY_ATOMIC_ZEROPAGE) {
> > d8ed45c5dcd455 Michel Lespinasse 2020-06-08  231                mmap_read_unlock(dst_mm);
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  232                return -EINVAL;
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  233        }
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  234
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  235        src_addr = src_start;
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  236        dst_addr = dst_start;
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  237        copied = 0;
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  238        page = NULL;
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  239        vma_hpagesize = vma_kernel_pagesize(dst_vma);
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  240
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  241        /*
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  242         * Validate alignment based on huge page size
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  243         */
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  244        err = -EINVAL;
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  245        if (dst_start & (vma_hpagesize - 1) || len & (vma_hpagesize - 1))
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  246                goto out_unlock;
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  247
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  248  retry:
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  249        /*
> > c1e8d7c6a7a682 Michel Lespinasse 2020-06-08  250         * On routine entry dst_vma is set.  If we had to drop mmap_lock and
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  251         * retry, dst_vma will be set to NULL and we must lookup again.
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  252         */
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  253        if (!dst_vma) {
> > 27d02568f529e9 Mike Rapoport     2017-02-24  254                err = -ENOENT;
> > 643aa36eadebdc Wei Yang          2019-11-30  255                dst_vma = find_dst_vma(dst_mm, dst_start, len);
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  256                if (!dst_vma || !is_vm_hugetlb_page(dst_vma))
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  257                        goto out_unlock;
> > 1c9e8def43a345 Mike Kravetz      2017-02-22  258
> > 27d02568f529e9 Mike Rapoport     2017-02-24  259                err = -EINVAL;
> > 27d02568f529e9 Mike Rapoport     2017-02-24  260                if (vma_hpagesize != vma_kernel_pagesize(dst_vma))
> > 27d02568f529e9 Mike Rapoport     2017-02-24  261                        goto out_unlock;
> > 27d02568f529e9 Mike Rapoport     2017-02-24  262
> > 1c9e8def43a345 Mike Kravetz      2017-02-22  263                vm_shared = dst_vma->vm_flags & VM_SHARED;
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  264        }
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  265
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  266        /*
> > 1c9e8def43a345 Mike Kravetz      2017-02-22  267         * If not shared, ensure the dst_vma has a anon_vma.
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  268         */
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  269        err = -ENOMEM;
> > 1c9e8def43a345 Mike Kravetz      2017-02-22  270        if (!vm_shared) {
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  271                if (unlikely(anon_vma_prepare(dst_vma)))
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  272                        goto out_unlock;
> > 1c9e8def43a345 Mike Kravetz      2017-02-22  273        }
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  274
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  275        while (src_addr < src_start + len) {
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  276                BUG_ON(dst_addr >= dst_start + len);
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  277
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  278                /*
> > c0d0381ade7988 Mike Kravetz      2020-04-01  279                 * Serialize via i_mmap_rwsem and hugetlb_fault_mutex.
> > c0d0381ade7988 Mike Kravetz      2020-04-01  280                 * i_mmap_rwsem ensures the dst_pte remains valid even
> > c0d0381ade7988 Mike Kravetz      2020-04-01  281                 * in the case of shared pmds.  fault mutex prevents
> > c0d0381ade7988 Mike Kravetz      2020-04-01  282                 * races with other faulting threads.
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  283                 */
> > ddeaab32a89f04 Mike Kravetz      2019-01-08  284                mapping = dst_vma->vm_file->f_mapping;
> > c0d0381ade7988 Mike Kravetz      2020-04-01  285                i_mmap_lock_read(mapping);
> > c0d0381ade7988 Mike Kravetz      2020-04-01  286                idx = linear_page_index(dst_vma, dst_addr);
> > 188b04a7d93860 Wei Yang          2019-11-30  287                hash = hugetlb_fault_mutex_hash(mapping, idx);
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  288                mutex_lock(&hugetlb_fault_mutex_table[hash]);
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  289
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  290                err = -ENOMEM;
> > aec44e0f0213e3 Peter Xu          2021-05-04  291                dst_pte = huge_pte_alloc(dst_mm, dst_vma, dst_addr, vma_hpagesize);
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  292                if (!dst_pte) {
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  293                        mutex_unlock(&hugetlb_fault_mutex_table[hash]);
> > c0d0381ade7988 Mike Kravetz      2020-04-01  294                        i_mmap_unlock_read(mapping);
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  295                        goto out_unlock;
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  296                }
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  297
> > f619147104c8ea Axel Rasmussen    2021-05-04  298                if (mode != MCOPY_ATOMIC_CONTINUE &&
> > f619147104c8ea Axel Rasmussen    2021-05-04  299                    !huge_pte_none(huge_ptep_get(dst_pte))) {
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  300                        err = -EEXIST;
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  301                        mutex_unlock(&hugetlb_fault_mutex_table[hash]);
> > c0d0381ade7988 Mike Kravetz      2020-04-01  302                        i_mmap_unlock_read(mapping);
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  303                        goto out_unlock;
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  304                }
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  305
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  306                err = hugetlb_mcopy_atomic_pte(dst_mm, dst_pte, dst_vma,
> > f619147104c8ea Axel Rasmussen    2021-05-04  307                                               dst_addr, src_addr, mode, &page);
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  308
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  309                mutex_unlock(&hugetlb_fault_mutex_table[hash]);
> > c0d0381ade7988 Mike Kravetz      2020-04-01  310                i_mmap_unlock_read(mapping);
> > 1c9e8def43a345 Mike Kravetz      2017-02-22  311                vm_alloc_shared = vm_shared;
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  312
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  313                cond_resched();
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  314
> > 9e368259ad9883 Andrea Arcangeli  2018-11-30  315                if (unlikely(err == -ENOENT)) {
> > d8ed45c5dcd455 Michel Lespinasse 2020-06-08  316                        mmap_read_unlock(dst_mm);
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  317                        BUG_ON(!page);
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  318
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  319                        err = copy_huge_page_from_user(page,
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  320                                                (const void __user *)src_addr,
> > 4fb07ee6510280 Wei Yang          2019-11-30  321                                                vma_hpagesize / PAGE_SIZE,
> > 4fb07ee6510280 Wei Yang          2019-11-30  322                                                true);
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  323                        if (unlikely(err)) {
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  324                                err = -EFAULT;
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  325                                goto out;
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  326                        }
> > d8ed45c5dcd455 Michel Lespinasse 2020-06-08  327                        mmap_read_lock(dst_mm);
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  328
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  329                        dst_vma = NULL;
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  330                        goto retry;
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  331                } else
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  332                        BUG_ON(page);
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  333
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  334                if (!err) {
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  335                        dst_addr += vma_hpagesize;
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  336                        src_addr += vma_hpagesize;
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  337                        copied += vma_hpagesize;
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  338
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  339                        if (fatal_signal_pending(current))
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  340                                err = -EINTR;
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  341                }
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  342                if (err)
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  343                        break;
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  344        }
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  345
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  346  out_unlock:
> > d8ed45c5dcd455 Michel Lespinasse 2020-06-08  347        mmap_read_unlock(dst_mm);
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  348  out:
> > 1786d001262006 Mina Almasry      2021-06-01  349        if (page)
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  350                put_page(page);
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  351        BUG_ON(copied < 0);
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  352        BUG_ON(err > 0);
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  353        BUG_ON(!copied && !err);
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  354        return copied ? copied : err;
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  355  }
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  356  #else /* !CONFIG_HUGETLB_PAGE */
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  357  /* fail at build time if gcc attempts to use this */
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  358  extern ssize_t __mcopy_atomic_hugetlb(struct mm_struct *dst_mm,
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  359                                      struct vm_area_struct *dst_vma,
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  360                                      unsigned long dst_start,
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  361                                      unsigned long src_start,
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  362                                      unsigned long len,
> > f619147104c8ea Axel Rasmussen    2021-05-04  363                                      enum mcopy_atomic_mode mode);
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  364  #endif /* CONFIG_HUGETLB_PAGE */
> > 60d4d2d2b40e44 Mike Kravetz      2017-02-22  365
> >
> > :::::: The code at line 212 was first introduced by commit
> > :::::: 1c9e8def43a3452e7af658b340f5f4f4ecde5c38 userfaultfd: hugetlbfs: add UFFDIO_COPY support for shared mappings
> >
> > :::::: TO: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
> > :::::: CC: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> >
> > ---
> > 0-DAY CI Kernel Test Service, Intel Corporation
> > https://lists.01.org/hyperkitty/list/kbuild-all@xxxxxxxxxxxx
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