On Fri, 2017-08-04 at 09:04 -0600, Jens Axboe wrote: > Since we introduced blk-mq-sched, the tags->rqs[] array has been > dynamically assigned. So we need to check for NULL when iterating, > since there's a window of time where the bit is set, but we haven't > dynamically assigned the tags->rqs[] array position yet. > > This is perfectly safe, since the memory backing of the request is > never going away while the device is alive. > > Signed-off-by: Jens Axboe <[email protected]> > --- > block/blk-mq-tag.c | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c > index d0be72ccb091..b856b2827157 100644 > --- a/block/blk-mq-tag.c > +++ b/block/blk-mq-tag.c > @@ -214,7 +214,7 @@ static bool bt_iter(struct sbitmap *bitmap, unsigned int > bitnr, void *data) > bitnr += tags->nr_reserved_tags; > rq = tags->rqs[bitnr]; > > - if (rq->q == hctx->queue) > + if (rq && rq->q == hctx->queue) > iter_data->fn(hctx, rq, iter_data->data, reserved); > return true; > } > @@ -249,8 +249,8 @@ static bool bt_tags_iter(struct sbitmap *bitmap, unsigned > int bitnr, void *data) > if (!reserved) > bitnr += tags->nr_reserved_tags; > rq = tags->rqs[bitnr]; > - > - iter_data->fn(rq, iter_data->data, reserved); > + if (rq) > + iter_data->fn(rq, iter_data->data, reserved); > return true; > }
Hello Jens, Should it have been mentioned in the patch description or in a comment that these functions can read tags->rqs[] after the corresponding bit has been set in the bitmap but before the tags->rqs[] pointer is updated? Anyway: Reviewed-by: Bart Van Assche <[email protected]>
