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Fri, 14 Apr 2023 19:48:36 +0000 (GMT) From: Tarun Sahu To: linux-mm@kvack.org Cc: akpm@linux-foundation.org, muchun.song@linux.dev, mike.kravetz@oracle.com, aneesh.kumar@linux.ibm.com, willy@infradead.org, sidhartha.kumar@oracle.com, gerald.schaefer@linux.ibm.com, linux-kernel@vger.kernel.org, jaypatel@linux.ibm.com, tsahu@linux.ibm.com Subject: [PATCH] mm/folio: Avoid special handling for order value 0 in folio_set_order Date: Sat, 15 Apr 2023 01:18:32 +0530 Message-Id: <20230414194832.973194-1-tsahu@linux.ibm.com> X-Mailer: git-send-email 2.31.1 X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: 3i7m5OSu9A-wYDstwtiRq8slVmQrLv6q X-Proofpoint-GUID: 3i7m5OSu9A-wYDstwtiRq8slVmQrLv6q X-Proofpoint-UnRewURL: 0 URL was un-rewritten MIME-Version: 1.0 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.254,Aquarius:18.0.942,Hydra:6.0.573,FMLib:17.11.170.22 definitions=2023-04-14_12,2023-04-14_01,2023-02-09_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 spamscore=0 impostorscore=0 lowpriorityscore=0 malwarescore=0 phishscore=0 clxscore=1011 mlxlogscore=999 adultscore=0 bulkscore=0 mlxscore=0 suspectscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2303200000 definitions=main-2304140174 X-Spam-Status: No, score=-2.0 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_EF,SPF_HELO_NONE,SPF_PASS,T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-getmail-retrieved-from-mailbox: =?utf-8?q?INBOX?= X-GMAIL-THRID: =?utf-8?q?1763182713224068256?= X-GMAIL-MSGID: =?utf-8?q?1763182713224068256?= folio_set_order(folio, 0); which is an abuse of folio_set_order as 0-order folio does not have any tail page to set order. folio->_folio_nr_pages is set to 0 for order 0 in folio_set_order. It is required because _folio_nr_pages overlapped with page->mapping and leaving it non zero caused "bad page" error while freeing gigantic hugepages. This was fixed in Commit ba9c1201beaa ("mm/hugetlb: clear compound_nr before freeing gigantic pages"). Also commit a01f43901cfb ("hugetlb: be sure to free demoted CMA pages to CMA") now explicitly clear page->mapping and hence we won't see the bad page error even if _folio_nr_pages remains unset. Also the order 0 folios are not supposed to call folio_set_order, So now we can get rid of folio_set_order(folio, 0) from hugetlb code path to clear the confusion. The patch also moves _folio_set_head and folio_set_order calls in __prep_compound_gigantic_folio() such that we avoid clearing them in the error path. Testing: I have run LTP tests, which all passes. and also I have written the test in LTP which tests the bug caused by compound_nr and page->mapping overlapping. https://lore.kernel.org/all/20230413090753.883953-1-tsahu@linux.ibm.com/ Running on older kernel ( < 5.10-rc7) with the above bug this fails while on newer kernel and, also with this patch it passes. Signed-off-by: Tarun Sahu --- mm/hugetlb.c | 9 +++------ mm/internal.h | 8 ++------ 2 files changed, 5 insertions(+), 12 deletions(-) diff --git a/mm/hugetlb.c b/mm/hugetlb.c index f16b25b1a6b9..e2540269c1dc 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -1489,7 +1489,6 @@ static void __destroy_compound_gigantic_folio(struct folio *folio, set_page_refcounted(p); } - folio_set_order(folio, 0); __folio_clear_head(folio); } @@ -1951,9 +1950,6 @@ static bool __prep_compound_gigantic_folio(struct folio *folio, struct page *p; __folio_clear_reserved(folio); - __folio_set_head(folio); - /* we rely on prep_new_hugetlb_folio to set the destructor */ - folio_set_order(folio, order); for (i = 0; i < nr_pages; i++) { p = folio_page(folio, i); @@ -1999,6 +1995,9 @@ static bool __prep_compound_gigantic_folio(struct folio *folio, if (i != 0) set_compound_head(p, &folio->page); } + __folio_set_head(folio); + /* we rely on prep_new_hugetlb_folio to set the destructor */ + folio_set_order(folio, order); atomic_set(&folio->_entire_mapcount, -1); atomic_set(&folio->_nr_pages_mapped, 0); atomic_set(&folio->_pincount, 0); @@ -2017,8 +2016,6 @@ static bool __prep_compound_gigantic_folio(struct folio *folio, p = folio_page(folio, j); __ClearPageReserved(p); } - folio_set_order(folio, 0); - __folio_clear_head(folio); return false; } diff --git a/mm/internal.h b/mm/internal.h index 18cda26b8a92..0d96a3bc1d58 100644 --- a/mm/internal.h +++ b/mm/internal.h @@ -425,16 +425,12 @@ int split_free_page(struct page *free_page, */ static inline void folio_set_order(struct folio *folio, unsigned int order) { - if (WARN_ON_ONCE(!folio_test_large(folio))) + if (WARN_ON_ONCE(!order || !folio_test_large(folio))) return; folio->_folio_order = order; #ifdef CONFIG_64BIT - /* - * When hugetlb dissolves a folio, we need to clear the tail - * page, rather than setting nr_pages to 1. - */ - folio->_folio_nr_pages = order ? 1U << order : 0; + folio->_folio_nr_pages = 1U << order; #endif }