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    SubjectRe: [PATCH] scsi: Fix qemu boot hang problem
    James, can you please send this on ASAP?  Sitting for oever a week
    on a boot regression that comes with a patch isn't reasonable.

    On Sun, Aug 10, 2014 at 05:54:25AM -0700, Guenter Roeck wrote:
    > 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 <hch@lst.de>
    > Cc: Hannes Reinecke <hare@suse.de>
    > Cc: Webb Scales <webbnh@hp.com>
    > Cc: Jens Axboe <axboe@kernel.dk>
    > Signed-off-by: Guenter Roeck <linux@roeck-us.net>
    > ---
    > 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
    >
    > --
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    ---end quoted text---


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