From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 6DD712C11E4; Mon, 11 May 2026 12:18:17 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778501897; cv=none; b=lIo7f79mY9Re4ywUwLtvXjeRR0PaWdOvbWQYx5dll2UbjvRKA+e+RWrFSHG8tapi5ud2FFYhkHfc9+zJuHOXRDbgpnR4Wsx+EgbjLv1V4rInSTjiKpZlFMCN6jlJIIE+ZyR/6k4dlspfNtVk1QonoiU0bqFNRUQAYKaOFqI0tm4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778501897; c=relaxed/simple; bh=yMjdymx8FHBrtj18YslQ/stGshcK0q1TjQd5LI7LL8Y=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=ZXdptBp2isnxxpWWbKuWFSil9QVvZQfE9UUSWTKJ7hNq1MLjiGCQqWr2rRO5qpGmDYshcutneKx3R4kGm1eY2H5oPIp2jCE2p8rPgNWVCEgXYNRhe/hhdA2pmznxzsd9cKhLtSx7VCcxqiO+nhXy+ZBn6N2fHy5B6CgwMgl5Pdo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=glGQBqNc; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="glGQBqNc" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 715CBC2BCB0; Mon, 11 May 2026 12:18:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1778501897; bh=yMjdymx8FHBrtj18YslQ/stGshcK0q1TjQd5LI7LL8Y=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=glGQBqNc1KRIJY+4eXYuyo4x8xsdMn7qscU1jXE+LdfRxl8N3+y7ch4kG0XZEC13w Rst3Ki2cfX5RVngCHsPWS3TxlWdiwjCqWw+mxwEzj76Ld9oGrEEE8izN+Qlfp09h6k GQ6fflH7jVvzFIHnmKXBit/AboWC0MKEQ9gPQ1sRrS2y4uRLI8NqMbhvYFWTGM/Iih G8dYr0EG5rZhZ1lvCP0hlskJ7cRHzE+lxy37XUjT538hZGp+rif9cejL7L5Uvjxmmn Fw15ZFguBcITOg3hc+tfABh/s03IszofdxDKfTadhI+XvKL1DGOGrxGHDxhg1QUZVw Sb6pbD0NFEMfg== Message-ID: Date: Mon, 11 May 2026 14:18:13 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 1/3] userfaultfd: ensure mremap_userfaultfd_fail() releases mmap_changing To: Mike Rapoport Cc: Andrew Morton , Alexander Viro , Christian Brauner , Jan Kara , Peter Xu , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org References: <20260501145433.156211-1-rppt@kernel.org> <20260501145433.156211-2-rppt@kernel.org> <3a04ae6a-049f-4d3d-b5c9-e60e86be8e5a@kernel.org> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 5/11/26 12:48, Mike Rapoport wrote: > On Mon, May 11, 2026 at 11:15:34AM +0200, David Hildenbrand (Arm) wrote: >> On 5/1/26 16:54, Mike Rapoport wrote: >>> From: "Mike Rapoport (Microsoft)" >>> >>> Sashiko says: >>> >>> mremap_userfaultfd_prep() increments ctx->mmap_changing to stall >>> concurrent operations, but mremap_userfaultfd_fail() does not >>> decrement it before dropping the context reference. >>> >>> If an mremap operation fails, ctx->mmap_changing remains elevated. This >>> will causes subsequent userfaultfd operations like a UFFDIO_COPY to fail >>> with -EAGAIN. >>> >> >> Sounds like we should CC stable? > > Yes. > >>> Decrement ctx->mmap_changing in mremap_userfaultfd_fail(). >>> >>> Link: https://sashiko.dev/#/patchset/20260430113512.115938-1-rppt@kernel.org >>> Fixes: df2cc96e7701 ("userfaultfd: prevent non-cooperative events vs mcopy_atomic races") >>> Signed-off-by: Mike Rapoport (Microsoft) >>> --- >>> fs/userfaultfd.c | 1 + >>> 1 file changed, 1 insertion(+) >>> >>> diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c >>> index 4b53dc4a3266..ef963a58f1a1 100644 >>> --- a/fs/userfaultfd.c >>> +++ b/fs/userfaultfd.c >>> @@ -786,6 +786,7 @@ void mremap_userfaultfd_fail(struct vm_userfaultfd_ctx *vm_ctx) >>> if (!ctx) >>> return; >>> >>> + atomic_dec(&ctx->mmap_changing); >> >> I'll note that other users have a >> >> VM_WARN_ON_ONCE(atomic_read(&ctx->mmap_changing) < 0); >> >> In there. Likely we should do the same? > > Yeah, we could. In any case Reviewed-by: David Hildenbrand (Arm) -- Cheers, David