From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jens Axboe Subject: Re: [PATCH] scsi: Fix qemu boot hang problem Date: Mon, 11 Aug 2014 08:12:17 -0600 Message-ID: <53E8CF41.2050300@kernel.dk> References: <1407675265-29192-1-git-send-email-linux@roeck-us.net> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1407675265-29192-1-git-send-email-linux@roeck-us.net> Sender: linux-kernel-owner@vger.kernel.org To: Guenter Roeck , "James E.J. Bottomley" Cc: linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org, Christoph Hellwig , Hannes Reinecke , Webb Scales List-Id: linux-scsi@vger.kernel.org On 2014-08-10 06:54, 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 > 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); > } > > That's a no-brainer obvious fix! Acked-by: Jens Axboe -- Jens Axboe