Re: [PATCH v2 2/4] mm: Probe for sub-page faults in fault_in_*()

[kernel test robot <lkp@intel.com>]

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Hi Catalin,

I love your patch! Perhaps something to improve:

[auto build test WARNING on powerpc/next]
[also build test WARNING on arm64/for-next/core linus/master v5.16-rc3]
[cannot apply to hnaz-mm/master kdave/for-next next-20211202]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch]

url:    https://github.com/0day-ci/linux/commits/Catalin-Marinas/Avoid-live-lock-in-fault-in-uaccess-loops-with-sub-page-faults/20211202-034030
base:   https://git.kernel.org/pub/scm/linux/kernel/git/powerpc/linux.git next
config: i386-randconfig-s001-20211128 (https://download.01.org/0day-ci/archive/20211202/202112022004.7fjmbELe-lkp(a)intel.com/config)
compiler: gcc-9 (Debian 9.3.0-22) 9.3.0
reproduce:
        # apt-get install sparse
        # sparse version: v0.6.4-dirty
        # https://github.com/0day-ci/linux/commit/a25817805b46cbc8d2d7e9d36dfa91e5f8dbf5df
        git remote add linux-review https://github.com/0day-ci/linux
        git fetch --no-tags linux-review Catalin-Marinas/Avoid-live-lock-in-fault-in-uaccess-loops-with-sub-page-faults/20211202-034030
        git checkout a25817805b46cbc8d2d7e9d36dfa91e5f8dbf5df
        # save the config file to linux build tree
        mkdir build_dir
        make W=1 C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__' O=build_dir ARCH=i386 SHELL=/bin/bash

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@intel.com>


sparse warnings: (new ones prefixed by >>)
>> mm/gup.c:1764:55: sparse: sparse: incorrect type in argument 1 (different modifiers) @@     expected void [noderef] __user *uaddr @@     got char const [noderef] __user *uaddr @@
   mm/gup.c:1764:55: sparse:     expected void [noderef] __user *uaddr
   mm/gup.c:1764:55: sparse:     got char const [noderef] __user *uaddr
>> mm/gup.c:1807:49: sparse: sparse: incorrect type in argument 1 (different modifiers) @@     expected void [noderef] __user *uaddr @@     got char const [noderef] __user *start @@
   mm/gup.c:1807:49: sparse:     expected void [noderef] __user *uaddr
   mm/gup.c:1807:49: sparse:     got char const [noderef] __user *start

vim +1764 mm/gup.c

  1700	
  1701	/*
  1702	 * fault_in_safe_writeable - fault in an address range for writing
  1703	 * @uaddr: start of address range
  1704	 * @size: length of address range
  1705	 * @min_size: minimum size to be faulted in
  1706	 *
  1707	 * Faults in an address range using get_user_pages, i.e., without triggering
  1708	 * hardware page faults.  This is primarily useful when we already know that
  1709	 * some or all of the pages in the address range aren't in memory.
  1710	 *
  1711	 * Other than fault_in_writeable(), this function is non-destructive.
  1712	 *
  1713	 * Note that we don't pin or otherwise hold the pages referenced that we fault
  1714	 * in.  There's no guarantee that they'll stay in memory for any duration of
  1715	 * time.
  1716	 *
  1717	 * Returns the number of bytes not faulted in, like copy_to_user() and
  1718	 * copy_from_user().
  1719	 */
  1720	size_t fault_in_safe_writeable(const char __user *uaddr, size_t size,
  1721				       size_t min_size)
  1722	{
  1723		unsigned long start = (unsigned long)untagged_addr(uaddr);
  1724		unsigned long end, nstart, nend;
  1725		struct mm_struct *mm = current->mm;
  1726		struct vm_area_struct *vma = NULL;
  1727		int locked = 0;
  1728		size_t faulted_in = size;
  1729	
  1730		nstart = start & PAGE_MASK;
  1731		end = PAGE_ALIGN(start + size);
  1732		if (end < nstart)
  1733			end = 0;
  1734		for (; nstart != end; nstart = nend) {
  1735			unsigned long nr_pages;
  1736			long ret;
  1737	
  1738			if (!locked) {
  1739				locked = 1;
  1740				mmap_read_lock(mm);
  1741				vma = find_vma(mm, nstart);
  1742			} else if (nstart >= vma->vm_end)
  1743				vma = vma->vm_next;
  1744			if (!vma || vma->vm_start >= end)
  1745				break;
  1746			nend = end ? min(end, vma->vm_end) : vma->vm_end;
  1747			if (vma->vm_flags & (VM_IO | VM_PFNMAP))
  1748				continue;
  1749			if (nstart < vma->vm_start)
  1750				nstart = vma->vm_start;
  1751			nr_pages = (nend - nstart) / PAGE_SIZE;
  1752			ret = __get_user_pages_locked(mm, nstart, nr_pages,
  1753						      NULL, NULL, &locked,
  1754						      FOLL_TOUCH | FOLL_WRITE);
  1755			if (ret <= 0)
  1756				break;
  1757			nend = nstart + ret * PAGE_SIZE;
  1758		}
  1759		if (locked)
  1760			mmap_read_unlock(mm);
  1761		if (nstart != end)
  1762			faulted_in = min_t(size_t, nstart - start, size);
  1763		if (faulted_in < min_size ||
> 1764		    (min_size && probe_subpage_safe_writeable(uaddr, min_size)))
  1765			return size;
  1766		return size - faulted_in;
  1767	}
  1768	EXPORT_SYMBOL(fault_in_safe_writeable);
  1769	
  1770	/**
  1771	 * fault_in_readable - fault in userspace address range for reading
  1772	 * @uaddr: start of user address range
  1773	 * @size: size of user address range
  1774	 * @min_size: minimum size to be faulted in
  1775	 *
  1776	 * Returns the number of bytes not faulted in (like copy_to_user() and
  1777	 * copy_from_user()).
  1778	 */
  1779	size_t fault_in_readable(const char __user *uaddr, size_t size,
  1780				 size_t min_size)
  1781	{
  1782		const char __user *start = uaddr, *end;
  1783		volatile char c;
  1784		size_t faulted_in = size;
  1785	
  1786		if (unlikely(size == 0))
  1787			return 0;
  1788		if (!PAGE_ALIGNED(uaddr)) {
  1789			if (unlikely(__get_user(c, uaddr) != 0))
  1790				return size;
  1791			uaddr = (const char __user *)PAGE_ALIGN((unsigned long)uaddr);
  1792		}
  1793		end = (const char __user *)PAGE_ALIGN((unsigned long)start + size);
  1794		if (unlikely(end < start))
  1795			end = NULL;
  1796		while (uaddr != end) {
  1797			if (unlikely(__get_user(c, uaddr) != 0))
  1798				goto out;
  1799			uaddr += PAGE_SIZE;
  1800		}
  1801	
  1802	out:
  1803		(void)c;
  1804		if (size > uaddr - start)
  1805			faulted_in = uaddr - start;
  1806		if (faulted_in < min_size ||
> 1807		    (min_size && probe_subpage_readable(start, min_size)))
  1808			return size;
  1809		return size - faulted_in;
  1810	}
  1811	EXPORT_SYMBOL(fault_in_readable);
  1812	

---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/kbuild-all(a)lists.01.org