From mboxrd@z Thu Jan 1 00:00:00 1970 From: Guenter Roeck Subject: [PATCH] scsi: Fix qemu boot hang problem Date: Sun, 10 Aug 2014 05:54:25 -0700 Message-ID: <1407675265-29192-1-git-send-email-linux@roeck-us.net> Return-path: Received: from mail-pd0-f170.google.com ([209.85.192.170]:65249 "EHLO mail-pd0-f170.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751400AbaHJMyb (ORCPT ); Sun, 10 Aug 2014 08:54:31 -0400 Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-scsi@vger.kernel.org To: "James E.J. Bottomley" Cc: linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org, Guenter Roeck , Christoph Hellwig , Hannes Reinecke , Webb Scales , Jens Axboe The latest kernel fails to boot qemu arm images when using scsi for disk access. Boot gets stuck after the following messages. brd: module loaded sym53c8xx 0000:00:0c.0: enabling device (0100 -> 0103) sym0: <895a> rev 0x0 at pci 0000:00:0c.0 irq 93 sym0: No NVRAM, ID 7, Fast-40, LVD, parity checking sym0: SCSI BUS has been reset. scsi host0: sym-2.2.3 Bisect points to commit 71e75c97f97a ("scsi: convert device_busy to atomic_t"). Code inspection shows the following suspicious change in scsi_request_fn. out_delay: - if (sdev->device_busy == 0 && !scsi_device_blocked(sdev)) + if (atomic_read(&sdev->device_busy) && !scsi_device_blocked(sdev)) blk_delay_queue(q, SCSI_QUEUE_DELAY); } 'sdev->device_busy == 0' was replaced with 'atomic_read(&sdev->device_busy)', meaning the logic was reversed. Changing this expression to '!atomic_read(&sdev->device_busy)' fixes the problem. Cc: Christoph Hellwig Cc: Hannes Reinecke Cc: Webb Scales Cc: Jens Axboe Signed-off-by: Guenter Roeck --- drivers/scsi/scsi_lib.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c index 9c44392..ce62e87 100644 --- a/drivers/scsi/scsi_lib.c +++ b/drivers/scsi/scsi_lib.c @@ -1774,7 +1774,7 @@ static void scsi_request_fn(struct request_queue *q) blk_requeue_request(q, req); atomic_dec(&sdev->device_busy); out_delay: - if (atomic_read(&sdev->device_busy) && !scsi_device_blocked(sdev)) + if (!atomic_read(&sdev->device_busy) && !scsi_device_blocked(sdev)) blk_delay_queue(q, SCSI_QUEUE_DELAY); } -- 1.9.1