From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 29BFD606A31F for ; Tue, 27 Oct 2026 08:32:01 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=NSyrEmFs Received: by kanga.kvack.org (Postfix) id 2B8A76B061D; Tue, 27 Oct 2026 04:32:00 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 2907F6B061F; Tue, 27 Oct 2026 04:32:00 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 1A5CD6B0620; Tue, 27 Oct 2026 04:32:00 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0012.hostedemail.com [216.40.44.12]) by kanga.kvack.org (Postfix) with ESMTP id D9F826B061D for ; Tue, 27 Oct 2026 04:31:59 -0400 (EDT) Received: from smtpin16.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay03.hostedemail.com (Postfix) with ESMTP id 6BA1BA0958 for ; Tue, 27 Oct 2026 08:31:59 +0000 (UTC) X-FDA: 85367738358.16.51C3AEF Received: from tor.source.kernel.org (tor.source.kernel.org [172.105.4.254]) by imf17.hostedemail.com (Postfix) with ESMTP id D85C340003 for ; Tue, 27 Oct 2026 08:31:57 +0000 (UTC) Authentication-Results: imf17.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=NSyrEmFs; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf17.hostedemail.com: domain of ljs@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=ljs@kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1793089917; 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-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=JYDAxb/IKfi0ONAEetWSuyzn9W1ajE3cX6VVYTxdndk=; b=5+d+8L4LiO/XPAe/tnBAmYm1gLGto6w9i8W63E8mIEFdh5VlpSP3V3l+QpqKgi3A6jtlbW P6nqDw+oGoPAQcQAZT4+/eU+nmOKocrQ8vMQAIYa2R+tp7GZYim4m9Cmvs4aquxQq5XCqr YXBvNbD0sGTiPu7cYb0awZH4558VgwY= ARC-Authentication-Results: i=1; imf17.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=NSyrEmFs; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf17.hostedemail.com: domain of ljs@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=ljs@kernel.org ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1793089917; b=0rmVkx0wfqBz+gaBioqgtSG9t2vMHYBXxInqQQjWxi+dnFFvq0YUZWhA6yFL0deDxa9Jh2 OMymrvBx2sqiKJ5rlGUeyNHZceqPInuSgyR9liAWQul0cmIpoZO4954hFJkKON1S0gzXwR 7rwLiuoCKQ5D0eU1CTtRcPZ5yGQPyT8= Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by tor.source.kernel.org (Postfix) with ESMTP id 4547B601FB; Tue, 27 Oct 2026 08:31:57 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 30FE51F01825; Tue, 27 Oct 2026 08:31:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793089917; bh=JYDAxb/IKfi0ONAEetWSuyzn9W1ajE3cX6VVYTxdndk=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=NSyrEmFsH2/8hgo8acOSrNLr9Hp/jrECdxCZNkIUtjazyxj1KHY2Z9xTuaK1Lx/+E ZlmTVVItxriaq2TTVszlyqWoslkxBKunusBgrpEBtjqe+GL7/BhgMfvr0j6wiA++no F2KtES+mT9pC9lUi/ceR10V31SP1W8sTkLdb8RXB5buLAYoTKBuslgPDKXcQC7fYaC tmT15Bau5bPVbn3Z1pAmnKqeU5kgzDR3je5XpPQh+1wLiPoL+vicuxqnXgb7RRv82r DFUEPhtPAu/EsK33zZwLXIqaPQ96HHeqGtj52+tHWqHJBcswjRzCsbgunsrigQ97JU n0Iy4vbd890bA== Date: Tue, 27 Oct 2026 08:31:40 +0000 From: "Lorenzo Stoakes (ARM)" To: "David Hildenbrand (Arm)" Cc: Andrew Morton , Johannes Weiner , Michal Hocko , Qi Zheng , Shakeel Butt , Kairui Song , Barry Song , Axel Rasmussen , Yuanchu Xie , Wei Xu , Baoquan He , Baolin Wang , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Kees Cook , Peter Zijlstra , Jann Horn , Pedro Falcato , Hugh Dickins , Pasha Tatashin , Pratyush Yadav , "Matthew Wilcox (Oracle)" , Jan Kara , Zi Yan , Lance Yang , Rik van Riel , Harry Yoo , Alistair Popple , Nico Pache , Ryan Roberts , Dev Jain , Usama Arif , Kiryl Shutsemau , Matthew Brost , John Hubbard , Peter Xu , Will Deacon , "Aneesh Kumar K.V" , Nick Piggin , Oscar Salvador , Minchan Kim , Muchun Song , Xu Xin , Chengming Zhou , Chris Li , Kemeng Shi , Nhat Pham , Youngjun Park , Gregory Price , Joshua Hahn , Rakie Kim , Ying Huang , Jason Gunthorpe , linux-mm@kvack.org, linux-kernel@vger.kernel.org, kexec@lists.infradead.org, linux-fsdevel@vger.kernel.org, linux-arch@vger.kernel.org, linux-cxl@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH 25/46] mm/userfaultfd: wake waiters when registration modes are removed Message-ID: References: <20261027-fixes_core-v1-0-6f74bec9a5bb@kernel.org> <20261027-fixes_core-v1-25-6f74bec9a5bb@kernel.org> X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261027-fixes_core-v1-25-6f74bec9a5bb@kernel.org> X-Rspamd-Queue-Id: D85C340003 X-Stat-Signature: p9yzzpbgrgxbse666nw536h6r7zuu4by X-Rspamd-Server: rspam04 X-Spam-Status: No, score=-16.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_PASS, SPF_PASS autolearn=unavailable autolearn_force=no version=4.0.1 X-Rspam-User: X-HE-Tag: 1793089917-127708 X-HE-Meta: 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 F7X8YkaS zs2J0lZwCgGS/HmytpVp30A/6ERea4GRaukykult+qNET7CDq5mSFiHcZvpcsEF9uxL1KiF2V+d3JqdTxK/3EkKK+R+tdaxSudKRNSFhkTocDBKiP43r+wZussBOd1l9MGXREKAbkctC4b1zfb29kWdPxycrgP5ItEC0980dzaKbAsOfzRXI00on/lanaJoYzet+n1zE+Ce89eaGOAop9CFLfZJG8efJXc99A68vVeAt01Xv7X2hMLwbQa0EOgCmUG53bEbRupiUWW2NhkXoYHR2E7YK/8Ih2lffpt5jFFrD4Hx8Qp3dBa05eGLK7hDNBIg7jgUyLO4CKlpdJId7D5gTb3EPSMOQpAOEd4drIxNmnCh9rw+GaqzoZDoQfDgvC3bWhsllgOF4P/1I= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On Tue, Oct 27, 2026 at 12:17:45AM +0100, David Hildenbrand (Arm) wrote: > UFFDIO_REGISTER can replace MISSING or MINOR tracking without waking > faults that are already queued. For example, switching an anonymous > range from MISSING to WP leaves a missing-fault waiter asleep until > userspace explicitly wakes it. I assume this is something people basically never do because you'd think it'd be a pretty obvious bug report right? > > When a registration change removes a UFFD mode, wake waiters in the > affected interval after updating the VMA. The VMA is write-locked at > this point, so no new faults can queue under the old modes and woken > threads cannot retry until mmap_write_unlock(). Waiters for retained > modes in the same interval may also wake and refault. Oh good lord. > > The hang reproduces for MISSING-to-WP and MINOR-to-MISSING transitions, > with both read and unread fault events. > > Fixes: 63b2d4174c4a ("userfaultfd: wp: add the writeprotect API to userfaultfd ioctl") > Cc: stable@vger.kernel.org > Signed-off-by: David Hildenbrand (Arm) In the words of Metallica, the more I see, the less, the less I believe... Reviewed-by: Lorenzo Stoakes (ARM) > --- > mm/userfaultfd.c | 20 ++++++++++++++++++++ > 1 file changed, 20 insertions(+) > > diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c > index 2122676c4220f..710e913c73bfa 100644 > --- a/mm/userfaultfd.c > +++ b/mm/userfaultfd.c > @@ -2270,6 +2270,9 @@ static struct vm_area_struct *userfaultfd_clear_vma(struct vma_iterator *vmi, > return ret; > } > > +static void wake_userfault_range(struct userfaultfd_ctx *ctx, > + unsigned long start, unsigned long end); > + > /* Assumes mmap write lock taken, and mm_struct pinned. */ > static int userfaultfd_register_range(struct userfaultfd_ctx *ctx, > struct vm_area_struct *vma, > @@ -2287,6 +2290,8 @@ static int userfaultfd_register_range(struct userfaultfd_ctx *ctx, > prev = vma; > > for_each_vma_range(vmi, vma, end) { > + const bool any_mode_removed = vma->vm_flags & __VM_UFFD_FLAGS & ~vm_flags; > + > cond_resched(); > > VM_WARN_ON_ONCE(!vma_can_userfault(vma, vm_flags, wp_async)); > @@ -2332,6 +2337,10 @@ static int userfaultfd_register_range(struct userfaultfd_ctx *ctx, > */ > userfaultfd_set_ctx(vma, ctx, vm_flags); > > + /* Retry faults for removed modes while the VMA is write-locked. */ > + if (any_mode_removed) > + wake_userfault_range(ctx, start, vma_end); > + > if (vma_is_hugetlb(vma) && uffd_disable_huge_pmd_share(vma)) > hugetlb_unshare_all_pmds(vma); > > @@ -3648,6 +3657,17 @@ static __always_inline void wake_userfault(struct userfaultfd_ctx *ctx, > __wake_userfault(ctx, range); > } > > +static void wake_userfault_range(struct userfaultfd_ctx *ctx, > + unsigned long start, unsigned long end) > +{ > + struct userfaultfd_wake_range range = { > + .start = start, > + .len = end - start, > + }; > + > + wake_userfault(ctx, &range); > +} > + > static __always_inline int validate_unaligned_range( > struct mm_struct *mm, __u64 start, __u64 len) > { > > -- > 2.43.0 > -- Cheers, Lorenzo