From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 7077BC02185 for ; Fri, 17 Jan 2025 07:44:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Transfer-Encoding: MIME-Version:References:In-Reply-To:Message-ID:Date:Subject:Cc:To:From: Reply-To:Content-Type:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=MJqlvj+lu/Tzo60R4fD2XZkdHzGxsT6TPL3RonbMnlI=; b=WMSdzvC8oTzdbMREAJdA6PFRDU UEydmN4rR1X8VdTJ8rK5BUuejrqI412KTtcc5253llbdDW4KW1r7fyDgxXp8qWafypSOPMfP6K0+W RcOAqebJ5bvLvrPhTAcqWAH7Z5mFSuu9CiAM5ENyOx35Wxwe3DbUO2Zcr5AfHHUHs3fgcxkXCB10T kk7jL04kRPqA00quRSEl6FWwJStgEeqCH3DOeDAIVE/10kqxBpV4COqLLuekiAZgXiJh4vcu9njIt 7IRTLFfTDCxykAMmqkhiKt9jzmEZT8HmByg98l/P0ZL/vHVFKa7SfswgN+2NEsyUwxwxzs2RwZvGD lTI1n4Vw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98 #2 (Red Hat Linux)) id 1tYh2B-0000000HEDt-03jP; Fri, 17 Jan 2025 07:44:51 +0000 Received: from 2a02-8389-2341-5b80-41c4-d87f-051e-5808.cable.dynamic.v6.surfer.at ([2a02:8389:2341:5b80:41c4:d87f:51e:5808] helo=localhost) by bombadil.infradead.org with esmtpsa (Exim 4.98 #2 (Red Hat Linux)) id 1tYh28-0000000HECO-38Y1; Fri, 17 Jan 2025 07:44:49 +0000 From: Christoph Hellwig To: Jens Axboe Cc: Ming Lei , linux-block@vger.kernel.org, nbd@other.debian.org, ceph-devel@vger.kernel.org, virtualization@lists.linux.dev, linux-mtd@lists.infradead.org, linux-nvme@lists.infradead.org, linux-scsi@vger.kernel.org Subject: [PATCH 1/2] loop: force GFP_NOIO for underlying file systems allocations Date: Fri, 17 Jan 2025 08:44:07 +0100 Message-ID: <20250117074442.256705-2-hch@lst.de> X-Mailer: git-send-email 2.45.2 In-Reply-To: <20250117074442.256705-1-hch@lst.de> References: <20250117074442.256705-1-hch@lst.de> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-BeenThere: linux-nvme@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "Linux-nvme" Errors-To: linux-nvme-bounces+linux-nvme=archiver.kernel.org@lists.infradead.org File systems can and often do allocate memory in the read-write path. If these allocations are done with __GFP_IO or __GFP_FS set they can recurse into the file system or swap device on top of the loop device and cause deadlocks. Prevent this by forcing a noio scope over the calls into the file system. Signed-off-by: Christoph Hellwig --- drivers/block/loop.c | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/drivers/block/loop.c b/drivers/block/loop.c index 1ec7417c7f00..71eccc5cfffb 100644 --- a/drivers/block/loop.c +++ b/drivers/block/loop.c @@ -1905,6 +1905,15 @@ static void loop_handle_cmd(struct loop_cmd *cmd) int ret = 0; struct mem_cgroup *old_memcg = NULL; const bool use_aio = cmd->use_aio; + unsigned int memflags; + + /* + * We're calling into file system which could do be doing memory + * allocations. Ensure the memory reclaim does not cause I/O, + * because that could end up in the user of this loop devices again and + * deadlock. + */ + memflags = memalloc_noio_save(); if (write && (lo->lo_flags & LO_FLAGS_READ_ONLY)) { ret = -EIO; @@ -1942,6 +1951,7 @@ static void loop_handle_cmd(struct loop_cmd *cmd) if (likely(!blk_should_fake_timeout(rq->q))) blk_mq_complete_request(rq); } + memalloc_noio_restore(memflags); } static void loop_process_work(struct loop_worker *worker, -- 2.45.2