From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 14F38C71157 for ; Tue, 17 Jun 2025 14:27:43 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id A36E76B0098; Tue, 17 Jun 2025 10:27:42 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 9E8E36B0099; Tue, 17 Jun 2025 10:27:42 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 8D7046B009A; Tue, 17 Jun 2025 10:27:42 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0013.hostedemail.com [216.40.44.13]) by kanga.kvack.org (Postfix) with ESMTP id 793B16B0098 for ; Tue, 17 Jun 2025 10:27:42 -0400 (EDT) Received: from smtpin05.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay04.hostedemail.com (Postfix) with ESMTP id 204D51A036B for ; Tue, 17 Jun 2025 14:27:42 +0000 (UTC) X-FDA: 83565121164.05.38E1D17 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by imf06.hostedemail.com (Postfix) with ESMTP id 2C23818000F for ; Tue, 17 Jun 2025 14:27:39 +0000 (UTC) Authentication-Results: imf06.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b="fCe0oVV/"; spf=pass (imf06.hostedemail.com: domain of luizcap@redhat.com designates 170.10.133.124 as permitted sender) smtp.mailfrom=luizcap@redhat.com; dmarc=pass (policy=quarantine) header.from=redhat.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1750170460; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=KDlgrgXxAg21YzMqYW6Qh6Z/vBEV3Xdk3QnBC6RuzMQ=; b=GTSnxkha3uRlw9xeXyFCF76XskNK5pwynK3nEK3Z84o7B0OECzEii+Xqove01lQn1Yijwn 9q0hLk5WvLYjjlEDFs9oBJRhiXV+CzsQCQ/jV9z3GNmlPWP6GgeyZCPMFUJFp8Rw2x9VcB 9Wx0staiPNoIy9Owg1Mbng1NRogBoTs= ARC-Authentication-Results: i=1; imf06.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b="fCe0oVV/"; spf=pass (imf06.hostedemail.com: domain of luizcap@redhat.com designates 170.10.133.124 as permitted sender) smtp.mailfrom=luizcap@redhat.com; dmarc=pass (policy=quarantine) header.from=redhat.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1750170460; a=rsa-sha256; cv=none; b=36/FvjJwGgkiJiEYpUS2/2KV6eB69L5PHGFexK16vRqV2AEjkf3K1Qw5ZKwLifWWbba994 3q7RZUrG5R4UajtPxwxXYRT4+ijoIfqjPJRu5lFoyNpy0nUcuuUGsAesx0t90I524Wf5Pw MfTeeOzhTy9aG87swTiUhPA3p3cbXA4= DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1750170459; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=KDlgrgXxAg21YzMqYW6Qh6Z/vBEV3Xdk3QnBC6RuzMQ=; b=fCe0oVV/uSWtX+4S+TvDvYG1RG5CWtZC3xezeQwAV+tHoiTlka3wDgq+ChlavWgHpLJ3QG zkzHpbRa0zy06GgRqjKroDWaNF1san1HbhMBfSluvemxiK0F4U1NCoTBYddCvQ3VPmAVmL Mv7i3rx67J/P6IMF38+dKrvgcQH9klM= Received: from mx-prod-mc-08.mail-002.prod.us-west-2.aws.redhat.com (ec2-35-165-154-97.us-west-2.compute.amazonaws.com [35.165.154.97]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-530-XSWUeR9EPlir_gCcV2Jq5w-1; Tue, 17 Jun 2025 10:27:36 -0400 X-MC-Unique: XSWUeR9EPlir_gCcV2Jq5w-1 X-Mimecast-MFC-AGG-ID: XSWUeR9EPlir_gCcV2Jq5w_1750170455 Received: from mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.12]) (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-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 0889D1809C8D; Tue, 17 Jun 2025 14:27:35 +0000 (UTC) Received: from fedora.redhat.com (unknown [10.22.80.174]) by mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id 8585619560A3; Tue, 17 Jun 2025 14:27:33 +0000 (UTC) From: Luiz Capitulino To: david@redhat.com, willy@infradead.org Cc: akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, lcapitulino@gmail.com, shivankg@amd.com Subject: [RFC 2/3] proc: kpagecount: use snapshot_page() Date: Tue, 17 Jun 2025 10:27:09 -0400 Message-ID: <35c0a0255d209db0de3d4881b956dc0581399c46.1750170418.git.luizcap@redhat.com> In-Reply-To: References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 3.0 on 10.30.177.12 X-Rspam-User: X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 2C23818000F X-Stat-Signature: hqix8urmd5janw9w5z7gqmxroz8m6bqw X-HE-Tag: 1750170459-520787 X-HE-Meta: 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 z7xgudrP RIS3Rz6t5y+tc5Xhd2A18vmUq4YuSlREhedt+05Ies8cn1G6L757GEn4Pe1O5MeORvbq3IUcTNie5P4OPrhOoSRltGVTL9juRX11/eYD+nUcKwDfWMS1cw1HD3uyydrxHifDctZ8Mei+CcCr4Z8LWzB4iJTspECFcFPW818Pv1lV3JVTeNkna1P5xqMz2Z38LiGPaOw1j7HyjWFXFdlcsymA3uBgW8VD4s7z6U5QQ41OQ6bMiTDhAJQuaSZFi/qkBxFmq+p/IXojMQaMEgtvLRBiGHMW5l62LPJN9NTH1oY19K31xEW85OzzN1fHf9P5J520un7OXH/2xG4+YV55vI4l/N1xDwfsSWGE/B3dH9nqKu5AzSZ1XnDpMLOUsS7dvllLE 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 retreive the folio mapcount using a folio snapshot. Splat: [ 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 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); -- 2.49.0