linux-kernel - Re: kernel BUG at block/blk-timeout.c:178!

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Date:	Thu, 04 Dec 2008 16:06:52 -0500
From:	"Alan D. Brunelle" <Alan.Brunelle@...com>
To:	"Alan D. Brunelle" <Alan.Brunelle@...com>
CC:	Jens Axboe <jens.axboe@...cle.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: kernel BUG at block/blk-timeout.c:178!

Alan D. Brunelle wrote:
> Alan D. Brunelle wrote:
>> Jens Axboe wrote:
>>
>>> Alan, can you try latest -git? feaf3848a813a106f163013af6fcf6c4bfec92d9
>>> or later.
>>>
>> git pull()ed to: feaf3848a813a106f163013af6fcf6c4bfec92d9 and the same
>> problem occurs.
> 
> Maybe not - I've not been to reproduce that problem in subsequent
> reboots. It could be that I booted the wrong kernel first time (rc6
> instead of rc7). Will keep plugging - any idea as to what might have
> "fixed" the problem between rc6 & rc7?
> 
> Alan

It's back - just not as easily reproduced as before.

I'm concerned over this piece of code:

/*
 * hp_sw_tur - Send TEST UNIT READY
 * @sdev: sdev command should be sent to
 *
 * Use the TEST UNIT READY command to determine
 * the path state.
 */
static int hp_sw_tur(struct scsi_device *sdev, struct hp_sw_dh_data *h)
{
        struct request *req;
        int ret;

        req = blk_get_request(sdev->request_queue, WRITE, GFP_NOIO);
        if (!req)
                return SCSI_DH_RES_TEMP_UNAVAIL;

        req->cmd_type = REQ_TYPE_BLOCK_PC;
        req->cmd_flags |= REQ_FAILFAST_DEV | REQ_FAILFAST_TRANSPORT |
                          REQ_FAILFAST_DRIVER;
        req->cmd_len = COMMAND_SIZE(TEST_UNIT_READY);
        req->cmd[0] = TEST_UNIT_READY;
        req->timeout = HP_SW_TIMEOUT;
        req->sense = h->sense;
        memset(req->sense, 0, SCSI_SENSE_BUFFERSIZE);
        req->sense_len = 0;

retry:
        ret = blk_execute_rq(req->q, NULL, req, 1);
        if (ret == -EIO) {
                if (req->sense_len > 0) {
                        ret = tur_done(sdev, h->sense);
                } else {
                        sdev_printk(KERN_WARNING, sdev,
                                    "%s: sending tur failed with %x\n",
                                    HP_SW_NAME, req->errors);
                        ret = SCSI_DH_IO;
                }
        } else {
                h->path_state = HP_SW_PATH_ACTIVE;
                ret = SCSI_DH_OK;
        }
        if (ret == SCSI_DH_IMM_RETRY)
                goto retry;
        if (ret == SCSI_DH_DEV_OFFLINED) {
                h->path_state = HP_SW_PATH_PASSIVE;
                ret = SCSI_DH_OK;
        }

        blk_put_request(req);

        return ret;
}

I've pushed the BUG ON check into blk_execute_rq, and it's finding it
set there. Could we be getting SCSI_DH_IMM_RETRYs and that's causing the
same request to be used without being re-initialized, and on error the
bit is not being cleaned up properly?

I'm checking that out next...

Alan
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