Hi Yang, kernel test robot noticed the following build warnings: [auto build test WARNING on akpm-mm/mm-everything] url: https://github.com/intel-lab-lkp/linux/commits/Yang-Shi/mm-gup-do-not-call-try_grab_folio-in-slow-path/20240605-075027 base: https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git mm-everything patch link: https://lore.kernel.org/r/20240604234858.948986-2-yang%40os.amperecomputing.com patch subject: [PATCH 2/2] mm: gup: do not call try_grab_folio() in slow path config: openrisc-allnoconfig (https://download.01.org/0day-ci/archive/20240605/202406051039.9m00gwIx-lkp@xxxxxxxxx/config) compiler: or1k-linux-gcc (GCC) 13.2.0 reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20240605/202406051039.9m00gwIx-lkp@xxxxxxxxx/reproduce) If you fix the issue in a separate patch/commit (i.e. not just a new version of the same patch/commit), kindly add following tags | Reported-by: kernel test robot <lkp@xxxxxxxxx> | Closes: https://lore.kernel.org/oe-kbuild-all/202406051039.9m00gwIx-lkp@xxxxxxxxx/ All warnings (new ones prefixed by >>): >> mm/gup.c:131:22: warning: 'try_grab_folio_fast' defined but not used [-Wunused-function] 131 | static struct folio *try_grab_folio_fast(struct page *page, int refs, | ^~~~~~~~~~~~~~~~~~~ vim +/try_grab_folio_fast +131 mm/gup.c 101 102 /** 103 * try_grab_folio_fast() - Attempt to get or pin a folio in fast path. 104 * @page: pointer to page to be grabbed 105 * @refs: the value to (effectively) add to the folio's refcount 106 * @flags: gup flags: these are the FOLL_* flag values. 107 * 108 * "grab" names in this file mean, "look at flags to decide whether to use 109 * FOLL_PIN or FOLL_GET behavior, when incrementing the folio's refcount. 110 * 111 * Either FOLL_PIN or FOLL_GET (or neither) must be set, but not both at the 112 * same time. (That's true throughout the get_user_pages*() and 113 * pin_user_pages*() APIs.) Cases: 114 * 115 * FOLL_GET: folio's refcount will be incremented by @refs. 116 * 117 * FOLL_PIN on large folios: folio's refcount will be incremented by 118 * @refs, and its pincount will be incremented by @refs. 119 * 120 * FOLL_PIN on single-page folios: folio's refcount will be incremented by 121 * @refs * GUP_PIN_COUNTING_BIAS. 122 * 123 * Return: The folio containing @page (with refcount appropriately 124 * incremented) for success, or NULL upon failure. If neither FOLL_GET 125 * nor FOLL_PIN was set, that's considered failure, and furthermore, 126 * a likely bug in the caller, so a warning is also emitted. 127 * 128 * It uses add ref unless zero to elevate the folio refcount and must be called 129 * in fast path only. 130 */ > 131 static struct folio *try_grab_folio_fast(struct page *page, int refs, 132 unsigned int flags) 133 { 134 struct folio *folio; 135 136 /* Raise warn if it is not called in fast GUP */ 137 VM_WARN_ON_ONCE(!irqs_disabled()); 138 139 if (WARN_ON_ONCE((flags & (FOLL_GET | FOLL_PIN)) == 0)) 140 return NULL; 141 142 if (unlikely(!(flags & FOLL_PCI_P2PDMA) && is_pci_p2pdma_page(page))) 143 return NULL; 144 145 if (flags & FOLL_GET) 146 return try_get_folio(page, refs); 147 148 /* FOLL_PIN is set */ 149 150 /* 151 * Don't take a pin on the zero page - it's not going anywhere 152 * and it is used in a *lot* of places. 153 */ 154 if (is_zero_page(page)) 155 return page_folio(page); 156 157 folio = try_get_folio(page, refs); 158 if (!folio) 159 return NULL; 160 161 /* 162 * Can't do FOLL_LONGTERM + FOLL_PIN gup fast path if not in a 163 * right zone, so fail and let the caller fall back to the slow 164 * path. 165 */ 166 if (unlikely((flags & FOLL_LONGTERM) && 167 !folio_is_longterm_pinnable(folio))) { 168 if (!put_devmap_managed_folio_refs(folio, refs)) 169 folio_put_refs(folio, refs); 170 return NULL; 171 } 172 173 /* 174 * When pinning a large folio, use an exact count to track it. 175 * 176 * However, be sure to *also* increment the normal folio 177 * refcount field at least once, so that the folio really 178 * is pinned. That's why the refcount from the earlier 179 * try_get_folio() is left intact. 180 */ 181 if (folio_test_large(folio)) 182 atomic_add(refs, &folio->_pincount); 183 else 184 folio_ref_add(folio, 185 refs * (GUP_PIN_COUNTING_BIAS - 1)); 186 /* 187 * Adjust the pincount before re-checking the PTE for changes. 188 * This is essentially a smp_mb() and is paired with a memory 189 * barrier in folio_try_share_anon_rmap_*(). 190 */ 191 smp_mb__after_atomic(); 192 193 node_stat_mod_folio(folio, NR_FOLL_PIN_ACQUIRED, refs); 194 195 return folio; 196 } 197 -- 0-DAY CI Kernel Test Service https://github.com/intel/lkp-tests/wiki
