From 480cadc2b7e0fa2bbab20141efb547dfe0c3707c Mon Sep 17 00:00:00 2001 From: Guenter Roeck Date: Sun, 10 Aug 2014 05:54:25 -0700 Subject: [PATCH] scsi: Fix qemu boot hang problem 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. Signed-off-by: Guenter Roeck Reviewed-by: Hannes Reinecke Acked-by: Jens Axboe Reviewed-by: Venkatesh Srinivas Reviewed-by: Webb Scales Cc: Christoph Hellwig Signed-off-by: Linus Torvalds --- 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 9c44392b748f..ce62e8798cc8 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); } -- 2.39.2