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Date: Mon, 11 Aug 2014 08:33:38 -0700 From: Venkatesh Srinivas <venkateshs@...gle.com> To: Jens Axboe <axboe@...nel.dk> Cc: Guenter Roeck <linux@...ck-us.net>, "James E.J. Bottomley" <JBottomley@...allels.com>, linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org, Christoph Hellwig <hch@....de>, Hannes Reinecke <hare@...e.de>, Webb Scales <webbnh@...com> Subject: Re: [PATCH] scsi: Fix qemu boot hang problem Should we wrap the sdev->device_busy read and test in a new scsi_device_busy(), so as to preserve the old polarity? Reviewed-by: Venkatesh Srinivas <venkateshs@...gle.com> On 8/11/14, Jens Axboe <axboe@...nel.dk> wrote: > 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 <hch@....de> >> Cc: Hannes Reinecke <hare@...e.de> >> Cc: Webb Scales <webbnh@...com> >> Cc: Jens Axboe <axboe@...nel.dk> >> Signed-off-by: Guenter Roeck <linux@...ck-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); >> } >> >> > > That's a no-brainer obvious fix! > > Acked-by: Jens Axboe <axboe@...com> > > > -- > Jens Axboe > > -- > To unsubscribe from this list: send the line "unsubscribe linux-scsi" in > the body of a message to majordomo@...r.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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