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 2E0AA175A6E; Tue, 5 May 2026 16:44:30 +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=1777999471; cv=none; b=JxOUPRdsJuLwIUY6MONOqTg0MSrMSH8wCXmWDFylk8zqIr+ZRp9XzNBvSEZWmMJcw7erlDSde9dUTi6ZwYbx5O6kTjYpmqyKR3Akmrxln6xf8FGqFww9jcaMqCBM+UurhuLtnSi9qPCWMqSjV7r2m66L7DtvR1PmvAI5rKj2MpQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777999471; c=relaxed/simple; bh=xj8LpSNbtv+j4xFJKQ9xt2fSol5GjGyuqBZaqt8GzDk=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=N0ovaMHCm+YeBZVaIyRyUycvomco0Vmdh9rX82qaQk79EZzTbQHNfJfW1eO+AtQADmezBjBX5C1iP+1x9AqVFmCH5cmOiWyNNqfE6t/mjBGWNvX37TivGR+wKdXLneQh2kIFhonQjrnWU2iWk5e3bqnkQOGZhL7+f856jsYUR4U= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Q01h7JvY; 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="Q01h7JvY" Received: by smtp.kernel.org (Postfix) with ESMTPSA id B8A48C2BCB4; Tue, 5 May 2026 16:44:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1777999470; bh=xj8LpSNbtv+j4xFJKQ9xt2fSol5GjGyuqBZaqt8GzDk=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=Q01h7JvYhPGcq3PfZNoE0gAwre7dTXNsj38xaKAFbFVAb4uD7tXqMulBkPzyCPxma MqrCuY/oiBZWH4EVZp3PibFaiJOdKeOOjOqwLxRk0CX3V3VqbZm594kpHEuAbbv+wJ pyNpqQkANgj6wCVlaeGkD0Xyer6kzLetbl9ULYgGOsxcH91xadO24utLUQZeP7YbXu fh+LzRCpT8C7M6Vi4DGjBqDgEOth18GbekfRs4r8l3VeBUAzLtUMhL02tGP9IdL6HZ VaDSBxVR0etvDr1oi1BMwUQhNuJCafsjKqD4d4OY5AfGOvwL2pS7bmrnx5oJoMWiux Tt8w32vSxAWpA== Date: Tue, 5 May 2026 09:44:28 -0700 From: "Darrick J. Wong" To: bernd@bsbernd.com Cc: joannelkoong@gmail.com, neal@gompa.dev, fuse-devel@lists.linux.dev, linux-fsdevel@vger.kernel.org, miklos@szeredi.hu Subject: [PATCH v1.1 1/2] libfuse: don't use SYNC_INIT unless asked for Message-ID: <20260505164428.GC7739@frogsfrogsfrogs> References: <177795853450.1133476.8692790530314969678.stgit@frogsfrogsfrogs> <177795853473.1133476.16730865173873586203.stgit@frogsfrogsfrogs> Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <177795853473.1133476.16730865173873586203.stgit@frogsfrogsfrogs> From: Darrick J. Wong fuse2fs calls fuse_main, then starts threads from ->init. It doesn't call fuse_daemonize_early_start because I haven't ported it to use any of the new APIs. I don't have io_uring enabled for fuse on my dev box. fuse_main calls fuse_session_mount calls fuse_session_mount_new_api calls session_start_sync_init. At the start of the function, se->want_sync_init, se->uring.enable, and daemonize.active are all false. The first branch is not taken, so we call FUSE_DEV_IOC_SYNC_INIT and enable sync_init even though the user didn't ask for that and didn't prepare for it either. FUSE_DEV_IOC_SYNC_INIT succeeds, so we send the synchronous FUSE_INIT from mount, which calls fuse2fs' init() method. That starts the background threads and returns. Upon return to the kernel, the mount() now succeeds, and the next thing that fuse_main does is call fuse_daemonize(). Since we didn't call fuse_daemonize_early_start, the daemonize forks the process and the threads die with the parent. If we didn't ask for SYNC_INIT, don't enable it. This is needed to maintain compatibility with older fuse servers that only support asynchronous FUSE_INIT. Fixes: 3e1101057aea57 ("fuse mount: Support synchronous FUSE_INIT (privileged daemon)") Signed-off-by: Darrick J. Wong --- v1.1: improve commit message, refine logging logic --- lib/fuse_lowlevel.c | 18 +++++++++++++++--- 1 file changed, 15 insertions(+), 3 deletions(-) diff --git a/lib/fuse_lowlevel.c b/lib/fuse_lowlevel.c index 0e16845d2f14ff..83158d02bb8827 100644 --- a/lib/fuse_lowlevel.c +++ b/lib/fuse_lowlevel.c @@ -4475,9 +4475,21 @@ static int session_start_sync_init(struct fuse_session *se, int fd) { int err, res; - if (!se->want_sync_init && - (se->uring.enable && !fuse_daemonize_is_used())) { - if (se->debug) + if (!se->want_sync_init) { + /* + * SYNC_INIT is required for io_uring to initialize without + * deadlocking the kernel if the fuse server crashes. + * + * !fuse_daemonize_is_used implies the fuse server doesn't know + * about any of the SYNC_INIT APIs, so we don't enable sync + * init or generate log messages. + */ + if (se->uring.enable) + fuse_log(FUSE_LOG_DEBUG, + "fuse: io_uring broken with async init\n"); + else if (!fuse_daemonize_is_used()) + ; /* empty */ + else if (se->debug) fuse_log(FUSE_LOG_DEBUG, "fuse: sync init not enabled\n"); return 0;