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 8F2A33CEB9A; Fri, 1 May 2026 14:54:42 +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=1777647282; cv=none; b=QhaeUJqPyGGv5BizmnQfUl80yGSbJVdpdY44J9V46S8ebrmWwQA3JLnfGyWt36YhrxeWI3OfhrLMdFEqP4iGTLwbhpfkEj3Ie00OOeyxBmk1TyFs2/LY6wUzBCW5A79Wrem60xdA4TlB5BJYyMbBGEr9MT7eED7Skw1FxBK6Npk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777647282; c=relaxed/simple; bh=sIdxJn2uWKCUgOB/jcXwOeB6VnuZjhcEA2rnh/yGasw=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=T7KsJt+edC59tUhj704kTOg3t3ve1qGh6MmpkMaiDAQxZOUu4f07ZseDqZsB8i5/UBRQMHKG3FgZYksuCBpA3Tuex5jNXe8kTpGCC9XCoEztoB0UCqTjrSVla2VCc3tt6Jz5pstnvrhQFCMfZ7S0lhgdKg6rrEt2OgwvJSV/Dq8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=aCWpnuFT; 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="aCWpnuFT" Received: by smtp.kernel.org (Postfix) with ESMTPSA id BC207C2BCB4; Fri, 1 May 2026 14:54:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1777647282; bh=sIdxJn2uWKCUgOB/jcXwOeB6VnuZjhcEA2rnh/yGasw=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=aCWpnuFTXV3upoj4UjPdpW1McawbKlnlCFBEeLNisCH0zC9aWEqdLEdLMJKuQcw+n bKBiKeo9aht3nZsrkK+rDHGoJzxDQPmcu12UOUCZIoWPKTH9WjcYywhpGlTbayCTe8 /tGF7q3lBktif4gkzAfQ+rYgdYJgizImzBILlUHRN0vfXeYsBSqEBLfo13RgnBAGrY jSKK8ythzvY8zLjL4DxRRCKaA1RHIBV5XkKszVHtqNr/OQI01bbn3362NHvfMg1Scd D0sAx3Jarg7VkGo3UTYZOjrTK6cimClDGb5e68fLG82Zq/ploz5vbriOdXTXGlJ7az RlGxBVemjSjBg== From: Mike Rapoport To: Andrew Morton Cc: Alexander Viro , Christian Brauner , David Hildenbrand , Jan Kara , Mike Rapoport , Peter Xu , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [PATCH v2 1/3] userfaultfd: ensure mremap_userfaultfd_fail() releases mmap_changing Date: Fri, 1 May 2026 17:54:31 +0300 Message-ID: <20260501145433.156211-2-rppt@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260501145433.156211-1-rppt@kernel.org> References: <20260501145433.156211-1-rppt@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 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. 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); userfaultfd_ctx_put(ctx); } -- 2.53.0