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Mon, 07 Jul 2025 14:51:09 -0400 X-MC-Unique: Oal1N4fVOl-1QPWbGse-TA-1 X-Mimecast-MFC-AGG-ID: Oal1N4fVOl-1QPWbGse-TA_1751914268 Received: from mx-prod-int-04.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-04.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.40]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-05.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id D353D1944A83; Mon, 7 Jul 2025 18:51:07 +0000 (UTC) Received: from fedora.redhat.com (unknown [10.22.80.96]) by mx-prod-int-04.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id 9260919560AB; Mon, 7 Jul 2025 18:51:06 +0000 (UTC) From: Luiz Capitulino To: david@redhat.com, willy@infradead.org, akpm@linux-foundation.org Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, shivankg@amd.com, sj@kernel.org Subject: [PATCH v2 3/4] proc: kpagecount: use snapshot_page() Date: Mon, 7 Jul 2025 14:50:45 -0400 Message-ID: <15f86615b7e4291ad040a64d45e56fd2bb578943.1751914235.git.luizcap@redhat.com> In-Reply-To: References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 3.0 on 10.30.177.40 X-Stat-Signature: 4njzra4jzr87fq8sk8x79rg31kmg594t X-Rspam-User: X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 75E3D4000E X-HE-Tag: 1751914271-702082 X-HE-Meta: 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 plignJR+ crAZIuU0AFCacWyz1RMClWHkVl2dD314eTruRKwrAFsLMEYZrPc/0kCMRDvwqso9lxvqTZM3KS+6OKYOraly7YPf8f+oUCXsXdnZlGBPoMoacd16aw3GBzE9A9ZuASwVph/LGvRReMuj+k/B1prjkeStenh2adNdJwh9J/n6ARExad8e5N9GP+/47+v0kQ59BUnQKXttBa28Hb/hupagC5aZt3AfqEW9ziHt2OI/fbo3StSwIb+LTUoXKzkD2kq+7zEGMJzV8zna9Mltxt6eeSLzYchIZqnay+sKXDJIGH6RqoZscOtEOdk3llh39QLsUf8lRBX9kMei07gkWWSsNWU9R7VgmBxvFX28oBOzhHPVdJlU2LurZEyVHKAozD3POCa+qXDhZRAM/uGQ0gvBxmzsLt9QKKOOm+OQnOWcrVrrqVgRDnNtxByBzKD3XCD6mo77mnFFnj15T4J1dHRkjOeuGtaOz2xzt9vx4PVo3rtpggYM= 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: List-Subscribe: List-Unsubscribe: Currently, the call to folio_precise_page_mapcount() from kpage_read() can race with a folio split. When the race happens we trigger a VM_BUG_ON_FOLIO() in folio_entire_mapcount() (see splat below). This commit fixes this race by using snapshot_page() so that we retrieve the folio mapcount using a folio snapshot. [ 2356.558576] page: refcount:1 mapcount:1 mapping:0000000000000000 index:0xffff85200 pfn:0x6f7c00 [ 2356.558748] memcg:ffff000651775780 [ 2356.558763] anon flags: 0xafffff60020838(uptodate|dirty|lru|owner_2|swapbacked|node=1|zone=2|lastcpupid=0xfffff) [ 2356.558796] raw: 00afffff60020838 fffffdffdb5d0048 fffffdffdadf7fc8 ffff00064c1629c1 [ 2356.558817] raw: 0000000ffff85200 0000000000000000 0000000100000000 ffff000651775780 [ 2356.558839] page dumped because: VM_BUG_ON_FOLIO(!folio_test_large(folio)) [ 2356.558882] ------------[ cut here ]------------ [ 2356.558897] kernel BUG at ./include/linux/mm.h:1103! [ 2356.558982] Internal error: Oops - BUG: 00000000f2000800 [#1] SMP [ 2356.564729] CPU: 8 UID: 0 PID: 1864 Comm: folio-split-rac Tainted: G S W 6.15.0+ #3 PREEMPT(voluntary) [ 2356.566196] Tainted: [S]=CPU_OUT_OF_SPEC, [W]=WARN [ 2356.566814] Hardware name: Red Hat KVM, BIOS edk2-20241117-3.el9 11/17/2024 [ 2356.567684] pstate: 60400005 (nZCv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--) [ 2356.568563] pc : kpage_read.constprop.0+0x26c/0x290 [ 2356.569605] lr : kpage_read.constprop.0+0x26c/0x290 [ 2356.569992] sp : ffff80008fb739b0 [ 2356.570263] x29: ffff80008fb739b0 x28: ffff00064aa69580 x27: 00000000ff000000 [ 2356.570842] x26: 0000fffffffffff8 x25: ffff00064aa69580 x24: ffff80008fb73ae0 [ 2356.571411] x23: 0000000000000001 x22: 0000ffff86c6e8b8 x21: 0000000000000008 [ 2356.571978] x20: 00000000006f7c00 x19: 0000ffff86c6e8b8 x18: 0000000000000000 [ 2356.572581] x17: 3630303066666666 x16: 0000000000000003 x15: 0000000000001000 [ 2356.573217] x14: 00000000ffffffff x13: 0000000000000004 x12: 00aaaaaa00aaaaaa [ 2356.577674] x11: 0000000000000000 x10: 00aaaaaa00aaaaaa x9 : ffffbf3afca6c300 [ 2356.578332] x8 : 0000000000000002 x7 : 0000000000000001 x6 : 0000000000000001 [ 2356.578984] x5 : ffff000c79812408 x4 : 0000000000000000 x3 : 0000000000000000 [ 2356.579635] x2 : 0000000000000000 x1 : ffff00064aa69580 x0 : 000000000000003e [ 2356.580286] Call trace: [ 2356.580524] kpage_read.constprop.0+0x26c/0x290 (P) [ 2356.580982] kpagecount_read+0x28/0x40 [ 2356.581336] proc_reg_read+0x38/0x100 [ 2356.581681] vfs_read+0xcc/0x320 [ 2356.581992] ksys_read+0x74/0x118 [ 2356.582306] __arm64_sys_read+0x24/0x38 [ 2356.582668] invoke_syscall+0x70/0x100 [ 2356.583022] el0_svc_common.constprop.0+0x48/0xf8 [ 2356.583456] do_el0_svc+0x28/0x40 [ 2356.583930] el0_svc+0x38/0x118 [ 2356.584328] el0t_64_sync_handler+0x144/0x168 [ 2356.584883] el0t_64_sync+0x19c/0x1a0 [ 2356.585350] Code: aa0103e0 9003a541 91082021 97f813fc (d4210000) [ 2356.586130] ---[ end trace 0000000000000000 ]--- [ 2356.587377] note: folio-split-rac[1864] exited with irqs disabled [ 2356.588050] note: folio-split-rac[1864] exited with preempt_count 1 Reported-by: syzbot+3d7dc5eaba6b932f8535@syzkaller.appspotmail.com Closes: https://lore.kernel.org/all/67812fbd.050a0220.d0267.0030.GAE@google.com/ Acked-by: SeongJae Park Acked-by: David Hildenbrand Signed-off-by: Luiz Capitulino --- fs/proc/page.c | 21 +++++++++++++++++---- 1 file changed, 17 insertions(+), 4 deletions(-) diff --git a/fs/proc/page.c b/fs/proc/page.c index 999af26c7298..936f8bbe5a6f 100644 --- a/fs/proc/page.c +++ b/fs/proc/page.c @@ -43,6 +43,22 @@ static inline unsigned long get_max_dump_pfn(void) #endif } +static u64 get_kpage_count(const struct page *page) +{ + struct page_snapshot ps; + u64 ret; + + snapshot_page(&ps, page); + + if (IS_ENABLED(CONFIG_PAGE_MAPCOUNT)) + ret = folio_precise_page_mapcount(&ps.folio_snapshot, + &ps.page_snapshot); + else + ret = folio_average_page_mapcount(&ps.folio_snapshot); + + return ret; +} + static ssize_t kpage_read(struct file *file, char __user *buf, size_t count, loff_t *ppos, enum kpage_operation op) @@ -75,10 +91,7 @@ static ssize_t kpage_read(struct file *file, char __user *buf, info = stable_page_flags(page); break; case KPAGE_COUNT: - if (IS_ENABLED(CONFIG_PAGE_MAPCOUNT)) - info = folio_precise_page_mapcount(page_folio(page), page); - else - info = folio_average_page_mapcount(page_folio(page)); + info = get_kpage_count(page); break; case KPAGE_CGROUP: info = page_cgroup_ino(page); -- 2.50.0