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 5E5603ACF1A; Mon, 11 May 2026 09:15:38 +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=1778490938; cv=none; b=ADCLt/lsP9BP2x6ERVINKfiYq2leMXMl8RM3wS/6UGTmYCfkcYIUqdgLoFba+Im0V9WgPz4/x9MBjZ6YD738uarv6iET4irQMjW1m5FuP8OI9S51E/Cw9D0UccT0DQLZAu4ne2xpN/EWwxSxqpmQNA1nzqw0c2NAwS/XHjBn8Lg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778490938; c=relaxed/simple; bh=UtZQ2M+zSovzc0lXuXD92/mA5wpJzOmMGuyvzsAw/UA=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=JJeGfg7o46SHNW1jRC+WeBAkI1iMHbR2IlxG6u3AvHYxyWa7us3/cW+6rEc4elTU0NYynjM4VinP34G3XfPeNY8/SvcpLF/qDmXejwAt/MVJBBntvlwLSFQwhV/wBMxKEWhvWQzyl9A+BPTIEyvTEEF1kgbb8s8JgOhcYOmndGE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=YXv1Nkm3; 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="YXv1Nkm3" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4D363C2BCB0; Mon, 11 May 2026 09:15:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1778490938; bh=UtZQ2M+zSovzc0lXuXD92/mA5wpJzOmMGuyvzsAw/UA=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=YXv1Nkm3xbY6GJx8oQhu2MsMgulMHa/cQoMnyJw1P1KEgOk/H/al3/FHoNEDlhm3C dizgRDOwzPBdRREetZv+k2tzchrbJ5e06Gh26ci4WJZFzvtWYKhtXddU9Slgu/xmon X+mM1Y0hEdfrQjqkw8x9jvIRY1ASBq5lAWyxE0PCPHZqDqGSlVOwtGkFFJDK4W9MY+ ok4YO2iZIzBJqOtbfpEFr922lA4R9OlgMjkS9WvYERbGzP8FTBKcomH6anAsll7FY2 qXBtdy4Bhj9iXZ+j5kfgj8iqKfNTABUgAJNChvmy66GGpEudTfKBxwVE7xoQ/9+oIl /hQNGn7OAISxA== Message-ID: <3a04ae6a-049f-4d3d-b5c9-e60e86be8e5a@kernel.org> Date: Mon, 11 May 2026 11:15:34 +0200 Precedence: bulk X-Mailing-List: linux-fsdevel@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 , Andrew Morton Cc: 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> 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 5/1/26 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? > 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? -- Cheers, David