[linux-stable-rc:linux-5.4.y 3113/4278] mm/mempolicy.c:499:22: warning: variable 'mapped_pte' set but not used

[kernel test robot <lkp@xxxxxxxxx>]

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable-rc.git linux-5.4.y
head:   f52a40401ee9825556cc803c110c67bfec5f6b94
commit: c1f729c7dec0df04d62550d981af849f970a660d [3113/4278] mm: mempolicy: fix potential pte_unmap_unlock pte error
config: ia64-randconfig-r036-20210914 (attached as .config)
compiler: ia64-linux-gcc (GCC) 11.2.0
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/stable/linux-stable-rc.git/commit/?id=c1f729c7dec0df04d62550d981af849f970a660d
        git remote add linux-stable-rc https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable-rc.git
        git fetch --no-tags linux-stable-rc linux-5.4.y
        git checkout c1f729c7dec0df04d62550d981af849f970a660d
        # save the attached .config to linux build tree
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-11.2.0 make.cross ARCH=ia64 

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

All warnings (new ones prefixed by >>):

   In file included from arch/ia64/include/asm/pgtable.h:154,
                    from include/linux/mm.h:99,
                    from include/linux/dax.h:6,
                    from include/linux/mempolicy.h:11,
                    from mm/mempolicy.c:70:
   arch/ia64/include/asm/mmu_context.h: In function 'reload_context':
   arch/ia64/include/asm/mmu_context.h:137:48: warning: variable 'old_rr4' set but not used [-Wunused-but-set-variable]
     137 |         unsigned long rr0, rr1, rr2, rr3, rr4, old_rr4;
         |                                                ^~~~~~~
   mm/mempolicy.c: In function 'queue_pages_pte_range':
>> mm/mempolicy.c:499:22: warning: variable 'mapped_pte' set but not used [-Wunused-but-set-variable]
     499 |         pte_t *pte, *mapped_pte;
         |                      ^~~~~~~~~~


vim +/mapped_pte +499 mm/mempolicy.c

   478	
   479	/*
   480	 * Scan through pages checking if pages follow certain conditions,
   481	 * and move them to the pagelist if they do.
   482	 *
   483	 * queue_pages_pte_range() has three possible return values:
   484	 * 0 - pages are placed on the right node or queued successfully.
   485	 * 1 - there is unmovable page, and MPOL_MF_MOVE* & MPOL_MF_STRICT were
   486	 *     specified.
   487	 * -EIO - only MPOL_MF_STRICT was specified and an existing page was already
   488	 *        on a node that does not follow the policy.
   489	 */
   490	static int queue_pages_pte_range(pmd_t *pmd, unsigned long addr,
   491				unsigned long end, struct mm_walk *walk)
   492	{
   493		struct vm_area_struct *vma = walk->vma;
   494		struct page *page;
   495		struct queue_pages *qp = walk->private;
   496		unsigned long flags = qp->flags;
   497		int ret;
   498		bool has_unmovable = false;
 > 499		pte_t *pte, *mapped_pte;
   500		spinlock_t *ptl;
   501	
   502		ptl = pmd_trans_huge_lock(pmd, vma);
   503		if (ptl) {
   504			ret = queue_pages_pmd(pmd, ptl, addr, end, walk);
   505			if (ret != 2)
   506				return ret;
   507		}
   508		/* THP was split, fall through to pte walk */
   509	
   510		if (pmd_trans_unstable(pmd))
   511			return 0;
   512	
   513		mapped_pte = pte = pte_offset_map_lock(walk->mm, pmd, addr, &ptl);
   514		for (; addr != end; pte++, addr += PAGE_SIZE) {
   515			if (!pte_present(*pte))
   516				continue;
   517			page = vm_normal_page(vma, addr, *pte);
   518			if (!page)
   519				continue;
   520			/*
   521			 * vm_normal_page() filters out zero pages, but there might
   522			 * still be PageReserved pages to skip, perhaps in a VDSO.
   523			 */
   524			if (PageReserved(page))
   525				continue;
   526			if (!queue_pages_required(page, qp))
   527				continue;
   528			if (flags & (MPOL_MF_MOVE | MPOL_MF_MOVE_ALL)) {
   529				/* MPOL_MF_STRICT must be specified if we get here */
   530				if (!vma_migratable(vma)) {
   531					has_unmovable = true;
   532					break;
   533				}
   534	
   535				/*
   536				 * Do not abort immediately since there may be
   537				 * temporary off LRU pages in the range.  Still
   538				 * need migrate other LRU pages.
   539				 */
   540				if (migrate_page_add(page, qp->pagelist, flags))
   541					has_unmovable = true;
   542			} else
   543				break;
   544		}
   545		pte_unmap_unlock(mapped_pte, ptl);
   546		cond_resched();
   547	
   548		if (has_unmovable)
   549			return 1;
   550	
   551		return addr != end ? -EIO : 0;
   552	}
   553	

---
0-DAY CI Kernel Test Service, Intel Corporation
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