Re: [PATCH v3] mm/migrate.c: Rework migration_entry_wait() to not take a pageref

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

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Hi Alistair,

Thank you for the patch! Perhaps something to improve:

[auto build test WARNING on linux/master]
[also build test WARNING on linus/master v5.16-rc1 next-20211115]
[cannot apply to hnaz-mm/master]
[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/Alistair-Popple/mm-migrate-c-Rework-migration_entry_wait-to-not-take-a-pageref/20211115-185444
base:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git debe436e77c72fcee804fb867f275e6d31aa999c
config: i386-randconfig-r015-20211115 (attached as .config)
compiler: clang version 14.0.0 (https://github.com/llvm/llvm-project fbe72e41b99dc7994daac300d208a955be3e4a0a)
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://github.com/0day-ci/linux/commit/91a437ddc7606450e331059d80babe2d4c1163e0
        git remote add linux-review https://github.com/0day-ci/linux
        git fetch --no-tags linux-review Alistair-Popple/mm-migrate-c-Rework-migration_entry_wait-to-not-take-a-pageref/20211115-185444
        git checkout 91a437ddc7606450e331059d80babe2d4c1163e0
        # save the attached .config to linux build tree
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross W=1 ARCH=i386 

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

All warnings (new ones prefixed by >>):

>> mm/filemap.c:1447:6: warning: no previous prototype for function 'migration_entry_wait_on_locked' [-Wmissing-prototypes]
   void migration_entry_wait_on_locked(struct folio *folio, pte_t *ptep,
        ^
   mm/filemap.c:1447:1: note: declare 'static' if the function is not intended to be used outside of this translation unit
   void migration_entry_wait_on_locked(struct folio *folio, pte_t *ptep,
   ^
   static 
   1 warning generated.


vim +/migration_entry_wait_on_locked +1447 mm/filemap.c

  1428	
  1429	#ifdef CONFIG_MIGRATION
  1430	/**
  1431	 * migration_entry_wait_on_locked - Wait for a migration entry to be removed
  1432	 * @page: page referenced by the migration entry.
  1433	 * @ptep: mapped pte pointer. This function will return with the ptep unmapped.
  1434	 * @ptl: already locked ptl. This function will drop the lock.
  1435	 *
  1436	 * Wait for a migration entry referencing the given page to be removed. This is
  1437	 * equivalent to put_and_wait_on_page_locked(page, TASK_UNINTERRUPTIBLE) except
  1438	 * this can be called without taking a reference on the page. Instead this
  1439	 * should be called while holding the ptl for the migration entry referencing
  1440	 * the page.
  1441	 *
  1442	 * Returns after unmapping and unlocking the pte/ptl with pte_unmap_unlock().
  1443	 *
  1444	 * This follows the same logic as wait_on_page_bit_common() so see the comments
  1445	 * there.
  1446	 */
> 1447	void migration_entry_wait_on_locked(struct folio *folio, pte_t *ptep,
  1448					spinlock_t *ptl)
  1449	{
  1450		struct wait_page_queue wait_page;
  1451		wait_queue_entry_t *wait = &wait_page.wait;
  1452		bool thrashing = false;
  1453		bool delayacct = false;
  1454		unsigned long pflags;
  1455		wait_queue_head_t *q;
  1456	
  1457		q = folio_waitqueue(folio);
  1458		if (!folio_test_uptodate(folio) && folio_test_workingset(folio)) {
  1459			if (!folio_test_swapbacked(folio)) {
  1460				delayacct_thrashing_start();
  1461				delayacct = true;
  1462			}
  1463			psi_memstall_enter(&pflags);
  1464			thrashing = true;
  1465		}
  1466	
  1467		init_wait(wait);
  1468		wait->func = wake_page_function;
  1469		wait_page.folio = folio;
  1470		wait_page.bit_nr = PG_locked;
  1471		wait->flags = 0;
  1472	
  1473		spin_lock_irq(&q->lock);
  1474		folio_set_waiters(folio);
  1475		if (!folio_trylock_flag(folio, PG_locked, wait))
  1476			__add_wait_queue_entry_tail(q, wait);
  1477		spin_unlock_irq(&q->lock);
  1478	
  1479		/*
  1480		 * If a migration entry exists for the page the migration path must hold
  1481		 * a valid reference to the page, and it must take the ptl to remove the
  1482		 * migration entry. So the page is valid until the ptl is dropped.
  1483		 */
  1484		if (ptep)
  1485			pte_unmap_unlock(ptep, ptl);
  1486		else
  1487			spin_unlock(ptl);
  1488	
  1489		for (;;) {
  1490			unsigned int flags;
  1491	
  1492			set_current_state(TASK_UNINTERRUPTIBLE);
  1493	
  1494			/* Loop until we've been woken or interrupted */
  1495			flags = smp_load_acquire(&wait->flags);
  1496			if (!(flags & WQ_FLAG_WOKEN)) {
  1497				if (signal_pending_state(TASK_UNINTERRUPTIBLE, current))
  1498					break;
  1499	
  1500				io_schedule();
  1501				continue;
  1502			}
  1503			break;
  1504		}
  1505	
  1506		finish_wait(q, wait);
  1507	
  1508		if (thrashing) {
  1509			if (delayacct)
  1510				delayacct_thrashing_end();
  1511			psi_memstall_leave(&pflags);
  1512		}
  1513	}
  1514	#endif
  1515	

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

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