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    Subject[PATCH 4.9 093/105] scsi: sd: Do not override max_sectors_kb sysfs setting
    Date
    4.9-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Martin K. Petersen <martin.petersen@oracle.com>

    commit 77082ca503bed061f7fbda7cfd7c93beda967a41 upstream.

    A user may lower the max_sectors_kb setting in sysfs to accommodate
    certain workloads. Previously we would always set the max I/O size to
    either the block layer default or the optional preferred I/O size
    reported by the device.

    Keep the current heuristics for the initial setting of max_sectors_kb.
    For subsequent invocations, only update the current queue limit if it
    exceeds the capabilities of the hardware.

    Reported-by: Don Brace <don.brace@microsemi.com>
    Reviewed-by: Martin Wilck <mwilck@suse.com>
    Tested-by: Don Brace <don.brace@microsemi.com>
    Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    drivers/scsi/sd.c | 19 ++++++++++++++-----
    1 file changed, 14 insertions(+), 5 deletions(-)

    --- a/drivers/scsi/sd.c
    +++ b/drivers/scsi/sd.c
    @@ -2867,8 +2867,6 @@ static int sd_revalidate_disk(struct gen
    sd_read_write_same(sdkp, buffer);
    }

    - sdkp->first_scan = 0;
    -
    /*
    * We now have all cache related info, determine how we deal
    * with flush requests.
    @@ -2883,7 +2881,7 @@ static int sd_revalidate_disk(struct gen
    q->limits.max_dev_sectors = logical_to_sectors(sdp, dev_max);

    /*
    - * Use the device's preferred I/O size for reads and writes
    + * Determine the device's preferred I/O size for reads and writes
    * unless the reported value is unreasonably small, large, or
    * garbage.
    */
    @@ -2897,8 +2895,19 @@ static int sd_revalidate_disk(struct gen
    rw_max = min_not_zero(logical_to_sectors(sdp, dev_max),
    (sector_t)BLK_DEF_MAX_SECTORS);

    - /* Combine with controller limits */
    - q->limits.max_sectors = min(rw_max, queue_max_hw_sectors(q));
    + /* Do not exceed controller limit */
    + rw_max = min(rw_max, queue_max_hw_sectors(q));
    +
    + /*
    + * Only update max_sectors if previously unset or if the current value
    + * exceeds the capabilities of the hardware.
    + */
    + if (sdkp->first_scan ||
    + q->limits.max_sectors > q->limits.max_dev_sectors ||
    + q->limits.max_sectors > q->limits.max_hw_sectors)
    + q->limits.max_sectors = rw_max;
    +
    + sdkp->first_scan = 0;

    set_capacity(disk, logical_to_sectors(sdp, sdkp->capacity));
    sd_config_write_same(sdkp);

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