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    SubjectRe: [PATCH] blk: fix a wrong accounting of hd_struct->in_flight
    Date
    Hello,

    > From: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>
    >
    > /proc/diskstats would display a strange output as follows.
    >
    > $ cat /proc/diskstats |grep sda
    > 8 0 sda 90524 7579 102154 20464 0 0 0 0 0 14096 20089
    > 8 1 sda1 19085 1352 21841 4209 0 0 0 0 4294967064 15689 4293424691
    > ~~~~~~~~~~
    > 8 2 sda2 71252 3624 74891 15950 0 0 0 0 232 23995 1562390
    > 8 3 sda3 54 487 2188 92 0 0 0 0 0 88 92
    > 8 4 sda4 4 0 8 0 0 0 0 0 0 0 0
    > 8 5 sda5 81 2027 2130 138 0 0 0 0 0 87 137

    Hm, this is very nasty and crap.



    > @@ -1268,7 +1270,17 @@ static int __make_request(struct request
    > * not touch req->buffer either...
    > */
    > req->buffer = bio_data(bio);
    > + src_part = disk_map_sector_rcu(req->rq_disk, blk_rq_pos(req));
    > req->__sector = bio->bi_sector;
    > + dst_part = disk_map_sector_rcu(req->rq_disk, blk_rq_pos(req));

    I think this is wrong. disk_map_sector_rcu() require
    rcu read lock held (see function comment). all other call site take
    part_stat_lock() before disk_map_sector_rcu() call.





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