From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793089008; b=zJXEvYE49edRoCeY+vK+7Z1UYwy000o7pT3McSnROEEYs0BjU4IpZwydEpirvGeheMbd xpfi8fgu9FqrbizWa/QgHzanigfQ0o6ZmII2SqFv+oHgfxrOdQQzQTkUchFhFRxBEXTa6 kJnGtmClCDmJT9h3LmgMdIqF1UzmcesYOLxemk36U1pf47l5TMdSZ3gpL5MJ/9q7NdNQS 0ui1ZkkfvaBwKQAY9HcTeGlAUvwvFy3S6Qtg6yB/rJhRBBT3v4qT71msOcyQ2245Ov4v1 TeWJi5IBiqb8+VlTFWLucn8nvQL837EViQTIUC6QjUSjjXXAp2rhRMnmhzS3QHYpI9Q== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793089008; h=Received:DKIM-Signature:Date:From:To:Cc:Subject:Message-ID: References:MIME-Version:Content-Type:Content-Disposition:In-Reply-To; bh=25JoUd0Ca4DSucyqp8VdpaHvYyD4L6ugc8HcJwXmagI=; b=TsqjEmTxTtNdn9KrUJ34+Dk3iynC1OCRoK54pI/OoWcFY6UUF0MxnMsCfplIFkwzCOo3 t4cLNFuRj/UAhGnBb+6CXlI+IOakgvcQierxhybUCizN4BsyZYb6siI0hCsEAVIcOxXNP A6jeOwnVYhdSbJ5zbZviZqf+3enz58VuZk6yKn7L7cYQHuBStGd71R5QxwEcGTHY6rMrc yxPJvzpwKq3AdSsAEGRX7vQ5vxuTdfk7/6/HBYc+cmBEPC56DHMqn5WKgj9Gv5JI97A+H Q4yc4ApVhflwIn6rKU7nM/Aui6GDBvw+YSJV4WoO/oomtpcsI07byCHDHao/i/o4Txg== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=DqgW1ogH; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 52733606A31A; Tue, 27 Oct 2026 08:16:48 +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=DqgW1ogH Received: by smtp.kernel.org (Postfix) with ESMTPSA id EB6EE1F01825; Tue, 27 Oct 2026 08:16:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793089008; bh=25JoUd0Ca4DSucyqp8VdpaHvYyD4L6ugc8HcJwXmagI=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=DqgW1ogHskC3KjpnvkmfF/B2DYXhDZoPDNeziDRz5NYseOTPq/Bt3d/gR2uwOi5tt l0FKm0+vSEXyriWPhPAPthXH1Up+UF+85+8a4DRAWSbZRYMnvjqZUBuxtSS9VhexcH QjEToIVl39sflEhmYe9ziXX5NCu06RELjf5E7IRB4kHtHZXSvXfgKEoP26dOW1+9IE ffVmPh+WFa/36AqcOLOz1lEuekRW0rjPES5+SXPWLU9gfjD0+35/LrvlH8duWv+GbJ RuWAou4+YDgaZUIhlBwjRnVkYYWwTrj2jlqPucPxJ4gaehaWDjNNziTUjRRUgWOZSb cgzDt4LnM1kJg== Date: Tue, 27 Oct 2026 10:16:25 +0200 From: Mike Rapoport To: "David Hildenbrand (Arm)" Cc: Andrew Morton , Johannes Weiner , Michal Hocko , Qi Zheng , Shakeel Butt , Lorenzo Stoakes , Kairui Song , Barry Song , Axel Rasmussen , Yuanchu Xie , Wei Xu , Baoquan He , Baolin Wang , "Liam R. Howlett" , Vlastimil Babka , 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, Josef Bacik Subject: Re: [PATCH 23/46] mm/userfaultfd: write-lock the VMA before waking waiters when unregistering Message-ID: References: <20261027-fixes_core-v1-0-6f74bec9a5bb@kernel.org> <20261027-fixes_core-v1-23-6f74bec9a5bb@kernel.org> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261027-fixes_core-v1-23-6f74bec9a5bb@kernel.org> On Tue, Oct 27, 2026 at 12:17:43AM +0100, David Hildenbrand (Arm) wrote: > userfaultfd_unregister() wakes pending missing faults before clearing the > VMA's userfaultfd registration. With per-VMA fault locking, holding > mmap_lock for write does not prevent another fault from queuing after > the wakeup but before userfaultfd_clear_vma() write-locks the VMA. That > waiter can then remain asleep indefinitely. > > Call vma_start_write() before waking waiters. Existing fault handlers > queue themselves before dropping the VMA read lock, and new readers are > excluded until mmap_write_unlock(). > > Fixes: 29a22b9e08d7 ("mm: handle userfaults under VMA lock") > Cc: stable@vger.kernel.org > Reported-by: Josef Bacik > Signed-off-by: David Hildenbrand (Arm) Reviewed-by: Mike Rapoport (Microsoft) > --- > mm/userfaultfd.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c > index 669f71d485d02..7e30b5ff17be1 100644 > --- a/mm/userfaultfd.c > +++ b/mm/userfaultfd.c > @@ -3991,6 +3991,9 @@ static int userfaultfd_unregister(struct userfaultfd_ctx *ctx, > start = vma->vm_start; > vma_end = min(end, vma->vm_end); > > + /* Prevent new userfaults from being queued after the wakeup. */ > + vma_start_write(vma); > + > if (userfaultfd_missing(vma)) { > /* > * Wake any concurrent pending userfault while > > -- > 2.43.0 > -- Sincerely yours, Mike.