From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933926AbbCDGqW (ORCPT ); Wed, 4 Mar 2015 01:46:22 -0500 Received: from mail.linuxfoundation.org ([140.211.169.12]:43678 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933536AbbCDGVE (ORCPT ); Wed, 4 Mar 2015 01:21:04 -0500 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Tony Battersby , Douglas Gilbert , James Bottomley Subject: [PATCH 3.19 104/175] sg: fix EWOULDBLOCK errors with scsi-mq Date: Tue, 3 Mar 2015 22:14:42 -0800 Message-Id: <20150304061043.330011740@linuxfoundation.org> X-Mailer: git-send-email 2.3.1 In-Reply-To: <20150304061026.134125919@linuxfoundation.org> References: <20150304061026.134125919@linuxfoundation.org> User-Agent: quilt/0.64 MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-15 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.19-stable review patch. If anyone has any objections, please let me know. ------------------ From: Tony Battersby commit 7772855a996ec6e16944b120ab5ce21050279821 upstream. With scsi-mq enabled, userspace programs can get unexpected EWOULDBLOCK (a.k.a. EAGAIN) errors when submitting commands to the SCSI generic driver. Fix by calling blk_get_request() with GFP_KERNEL instead of GFP_ATOMIC. Note: to avoid introducing a potential deadlock, this patch should be applied after the patch titled "sg: fix unkillable I/O wait deadlock with scsi-mq". Signed-off-by: Tony Battersby Acked-by: Douglas Gilbert Tested-by: Douglas Gilbert Signed-off-by: James Bottomley Signed-off-by: Greg Kroah-Hartman --- drivers/scsi/sg.c | 17 ++++++++++++++++- 1 file changed, 16 insertions(+), 1 deletion(-) --- a/drivers/scsi/sg.c +++ b/drivers/scsi/sg.c @@ -1695,7 +1695,22 @@ sg_start_req(Sg_request *srp, unsigned c return -ENOMEM; } - rq = blk_get_request(q, rw, GFP_ATOMIC); + /* + * NOTE + * + * With scsi-mq enabled, there are a fixed number of preallocated + * requests equal in number to shost->can_queue. If all of the + * preallocated requests are already in use, then using GFP_ATOMIC with + * blk_get_request() will return -EWOULDBLOCK, whereas using GFP_KERNEL + * will cause blk_get_request() to sleep until an active command + * completes, freeing up a request. Neither option is ideal, but + * GFP_KERNEL is the better choice to prevent userspace from getting an + * unexpected EWOULDBLOCK. + * + * With scsi-mq disabled, blk_get_request() with GFP_KERNEL usually + * does not sleep except under memory pressure. + */ + rq = blk_get_request(q, rw, GFP_KERNEL); if (IS_ERR(rq)) { kfree(long_cmdp); return PTR_ERR(rq);