allow blk_flush_policy to return REQ_FSEQ_DATA independent of *FLUSH
authorJeff Moyer <jmoyer@redhat.com>
Tue, 9 Aug 2011 18:32:09 +0000 (20:32 +0200)
committerJens Axboe <jaxboe@fusionio.com>
Tue, 9 Aug 2011 18:32:09 +0000 (20:32 +0200)
commitfa1bf42ff9296ac4cf211b0a1b450a6071d26a95
tree0c7f43ca005c70022e64abb8b8d0b0d549b73959
parent4931402a9dd00b2997e95bfbb89409b2a6dbb383
allow blk_flush_policy to return REQ_FSEQ_DATA independent of *FLUSH

blk_insert_flush has the following check:

/*
 * If there's data but flush is not necessary, the request can be
 * processed directly without going through flush machinery.  Queue
 * for normal execution.
 */
if ((policy & REQ_FSEQ_DATA) &&
    !(policy & (REQ_FSEQ_PREFLUSH | REQ_FSEQ_POSTFLUSH))) {
list_add_tail(&rq->queuelist, &q->queue_head);
return;
}

However, blk_flush_policy will not return with policy set to only
REQ_FSEQ_DATA:

static unsigned int blk_flush_policy(unsigned int fflags, struct request *rq)
{
unsigned int policy = 0;

if (fflags & REQ_FLUSH) {
if (rq->cmd_flags & REQ_FLUSH)
policy |= REQ_FSEQ_PREFLUSH;
if (blk_rq_sectors(rq))
policy |= REQ_FSEQ_DATA;
if (!(fflags & REQ_FUA) && (rq->cmd_flags & REQ_FUA))
policy |= REQ_FSEQ_POSTFLUSH;
}
return policy;
}

Notice that REQ_FSEQ_DATA is only set if REQ_FLUSH is set.  Fix this
mismatch by moving the setting of REQ_FSEQ_DATA outside of the REQ_FLUSH
check.

Tejun notes:

  Hmmm... yes, this can become a correctness issue if (and only if)
  blk_queue_flush() is called to change q->flush_flags while requests
  are in-flight; otherwise, requests wouldn't reach the function at all.
  Also, I think it would be a generally good idea to always set
  FSEQ_DATA if the request has data.

Cheers,
Jeff

Signed-off-by: Jeff Moyer <jmoyer@redhat.com>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
block/blk-flush.c