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Mon, 15 May 2023 17:08:26 +0000 Received: from smtpav01.fra02v.mail.ibm.com (smtpav01.fra02v.mail.ibm.com [10.20.54.100]) by smtprelay03.fra02v.mail.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 34FH8NH93211900 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Mon, 15 May 2023 17:08:23 GMT Received: from smtpav01.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 5345E20043; Mon, 15 May 2023 17:08:23 +0000 (GMT) Received: from smtpav01.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id D805B20040; Mon, 15 May 2023 17:08:17 +0000 (GMT) Received: from tarunpc.ibmuc.com (unknown [9.43.21.157]) by smtpav01.fra02v.mail.ibm.com (Postfix) with ESMTP; Mon, 15 May 2023 17:08:17 +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 v2] mm/folio: Avoid special handling for order value 0 in folio_set_order Date: Mon, 15 May 2023 22:38:09 +0530 Message-Id: <20230515170809.284680-1-tsahu@linux.ibm.com> X-Mailer: git-send-email 2.31.1 X-TM-AS-GCONF: 00 X-Proofpoint-GUID: 4-rCbhDpET9mgBonILTZVw_0mH2M3-07 X-Proofpoint-ORIG-GUID: 4-rCbhDpET9mgBonILTZVw_0mH2M3-07 X-Proofpoint-UnRewURL: 0 URL was un-rewritten MIME-Version: 1.0 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.254,Aquarius:18.0.957,Hydra:6.0.573,FMLib:17.11.170.22 definitions=2023-05-15_15,2023-05-05_01,2023-02-09_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 lowpriorityscore=0 bulkscore=0 mlxlogscore=999 clxscore=1011 mlxscore=0 malwarescore=0 priorityscore=1501 impostorscore=0 suspectscore=0 spamscore=0 adultscore=0 phishscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2304280000 definitions=main-2305150143 X-Rspamd-Queue-Id: F308740013 X-Stat-Signature: x9mxwpww6gqz88gy1fqmukz8jotbeyqq X-Rspam-User: X-Rspamd-Server: rspam09 X-HE-Tag: 1684170553-941813 X-HE-Meta: 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 pHwqo79I n7V2rfm+JJNDDfPR83QRa5L11tfQ8t0I8nQzLrIauosQrqgZDwdexmctIfThMpdFmzTkXEsZEcmJLIEw2zcssU92Acx29Vmo3Ht4nzI+7bD+IRKLDTs0Mx9s0pKhkRQpXH7NeaY/kJIR5bttcnwSWYPmXMX4UyIVCbAtN0kmkZBJ1sbjFSqusTxVHRwiF6aAvDJEqXpmtrNRZpssaEJK5N1mCIQ== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: folio_set_order(folio, 0) is used in kernel at two places __destroy_compound_gigantic_folio and __prep_compound_gigantic_folio. Currently, It is called to clear out the folio->_folio_nr_pages and folio->_folio_order. For __destroy_compound_gigantic_folio: In past, folio_set_order(folio, 0) was needed because page->mapping used to overlap with _folio_nr_pages and _folio_order. So if these fields were left uncleared during freeing gigantic hugepages, they were causing "BUG: bad page state" due to non-zero page->mapping. Now, After Commit a01f43901cfb ("hugetlb: be sure to free demoted CMA pages to CMA") page->mapping has explicitly been cleared out for tail pages. Also, _folio_order and _folio_nr_pages no longer overlaps with page->mapping. struct page { ... struct address_space * mapping; /* 24 8 */ ... } struct folio { ... union { struct { long unsigned int _flags_1; /* 64 8 */ long unsigned int _head_1; /* 72 8 */ unsigned char _folio_dtor; /* 80 1 */ unsigned char _folio_order; /* 81 1 */ /* XXX 2 bytes hole, try to pack */ atomic_t _entire_mapcount; /* 84 4 */ atomic_t _nr_pages_mapped; /* 88 4 */ atomic_t _pincount; /* 92 4 */ unsigned int _folio_nr_pages; /* 96 4 */ }; /* 64 40 */ struct page __page_1 __attribute__((__aligned__(8))); /* 64 64 */ } ... } So, folio_set_order(folio, 0) can be removed from freeing gigantic folio path (__destroy_compound_gigantic_folio). Another place, folio_set_order(folio, 0) is called inside __prep_compound_gigantic_folio during error path. Here, folio_set_order(folio, 0) can also be removed if we move folio_set_order(folio, order) after for loop. The patch also moves _folio_set_head call in __prep_compound_gigantic_folio() such that we avoid clearing them in the error path. Also, as Mike pointed out: "It would actually be better to move the calls _folio_set_head and folio_set_order in __prep_compound_gigantic_folio() as suggested here. Why? In the current code, the ref count on the 'head page' is still 1 (or more) while those calls are made. So, someone could take a speculative ref on the page BEFORE the tail pages are set up." This way, folio_set_order(folio, 0) is no more needed. And it will also helps removing the confusion of folio order being set to 0 (as _folio_order field is part of first tail page). 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://github.com/linux-test-project/ltp/blob/master/testcases/kernel/mem/hugetlb/hugemmap/hugemmap32.c 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 f154019e6b84..607553445855 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 68410c6d97ac..c59fe08c5b39 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 }