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    SubjectRe: Linux 2.6.14: Badness in as-iosched
    On Thu, Nov 10 2005, Brice Goglin wrote:
    > Hi Jens,
    >
    > I just hit a badness (actually, tons of badness like this) in as-iosched
    > while ripping
    > an audio CD with ripperX (with cdparanoia as a backend).
    > I was using 2.6.14 on an IBM Thinkpad R52. The kernel has been compiled with
    > gcc-4.0.2-2 (Debian testing).
    >
    > The first badness in dmesg is:
    >
    > cdrom: dropping to single frame dma
    > arq->state: 4
    > Badness in as_insert_request at drivers/block/as-iosched.c:1519
    > [<c0237410>] as_insert_request+0x70/0x1d0
    > [<c022dc25>] __elv_add_request+0xa5/0xe0
    > [<c022dc8b>] elv_add_request+0x2b/0x40
    > [<c0230fe6>] blk_execute_rq_nowait+0x46/0x60
    > [<c023107a>] blk_execute_rq+0x7a/0xe0
    > [<c0231310>] blk_end_sync_rq+0x0/0x30
    > [<c0160b77>] bio_phys_segments+0x27/0x30
    > [<c0232610>] blk_rq_bio_prep+0x40/0xb0
    > [<c0230dc7>] blk_rq_map_user+0xb7/0xf0
    > [<c026bc32>] cdrom_read_cdda_bpc+0x182/0x210
    > [<c026bd1b>] cdrom_read_cdda+0x5b/0xc0

    Similar case was posted yesterday (I realize yours is older, just missed
    it the first time around), see my explanation here:

    http://lkml.org/lkml/2005/11/20/119

    And work-around below.

    diff --git a/drivers/cdrom/cdrom.c b/drivers/cdrom/cdrom.c
    index 1539603..7540d27 100644
    --- a/drivers/cdrom/cdrom.c
    +++ b/drivers/cdrom/cdrom.c
    @@ -2089,7 +2089,7 @@ static int cdrom_read_cdda_bpc(struct cd
    int lba, int nframes)
    {
    request_queue_t *q = cdi->disk->queue;
    - struct request *rq;
    + struct request *rq = NULL;
    struct bio *bio;
    unsigned int len;
    int nr, ret = 0;
    @@ -2097,13 +2097,13 @@ static int cdrom_read_cdda_bpc(struct cd
    if (!q)
    return -ENXIO;

    - rq = blk_get_request(q, READ, GFP_KERNEL);
    - if (!rq)
    - return -ENOMEM;
    -
    cdi->last_sense = 0;

    while (nframes) {
    + rq = blk_get_request(q, READ, GFP_KERNEL);
    + if (!rq)
    + return -ENOMEM;
    +
    nr = nframes;
    if (cdi->cdda_method == CDDA_BPC_SINGLE)
    nr = 1;
    @@ -2151,9 +2151,13 @@ static int cdrom_read_cdda_bpc(struct cd
    nframes -= nr;
    lba += nr;
    ubuf += len;
    + blk_put_request(rq);
    + rq = NULL;
    }

    - blk_put_request(rq);
    + if (rq)
    + blk_put_request(rq);
    +
    return ret;
    }

    --
    Jens Axboe

    -
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