On 08/04/2017 01:34 PM, Bart Van Assche wrote: > 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?
I'll add a comment to that effect. -- Jens Axboe
