Messages in this thread | | | Date | Fri, 25 Mar 2011 16:50:33 +0100 | From | Jens Axboe <> | Subject | Re: elevator private data for REQ_FLUSH |
| |
On 2011-03-25 16:40, Mike Snitzer wrote: > On Fri, Mar 25 2011 at 11:22am -0400, > Markus Trippelsdorf <markus@trippelsdorf.de> wrote: > >> On 2011.03.25 at 17:15 +0200, Sergey Senozhatsky wrote: >>> Hello, >>> >>> Commit >>> 9d5a4e946ce5352f19400b6370f4cd8e72806278 >>> block: skip elevator data initialization for flush requests >>> >>> Skip elevator initialization for flush requests by passing priv=0 to >>> blk_alloc_request() in get_request(). As such elv_set_request() is >>> never called for flush requests. >>> >>> introduced priv flag, to skip elevator_private data init for FLUSH requests. >>> This, I guess, lead to NULL pointer deref on my machine in cfq_insert_request, >>> which requires elevator_private to be set: >>> >>> 1 [ 78.982169] Call Trace: >>> 2 [ 78.982178] [<ffffffff8122d1fe>] cfq_insert_request+0x4e/0x47d >>> 3 [ 78.982184] [<ffffffff8123e139>] ? do_raw_spin_lock+0x6b/0x122 >> >>> Should we in that case use ELEVATOR_INSERT_FLUSH for REQ_FLUSH | REQ_FUA requests >>> (like below)? >>> >>> --- >>> >>> block/elevator.c | 2 ++ >>> 1 files changed, 2 insertions(+), 0 deletions(-) >>> >>> diff --git a/block/elevator.c b/block/elevator.c >>> index c387d31..b17e577 100644 >>> --- a/block/elevator.c >>> +++ b/block/elevator.c >>> @@ -734,6 +734,8 @@ void __elv_add_request(struct request_queue *q, struct request *rq, int where) >>> q->end_sector = rq_end_sector(rq); >>> q->boundary_rq = rq; >>> } >>> + } else if (rq->cmd_flags & (REQ_FLUSH | REQ_FUA)) { >>> + where = ELEVATOR_INSERT_FLUSH; >>> } else if (!(rq->cmd_flags & REQ_ELVPRIV) && >>> where == ELEVATOR_INSERT_SORT) >>> where = ELEVATOR_INSERT_BACK; >> >> Thanks. That solves all (corruption-) problems that I reported earlier in an other >> thread. > > So the flush-merge changes introduced ELEVATOR_INSERT_FLUSH (via commit > ae1b1539). And the flush bio will now get ELEVATOR_INSERT_FLUSH in > __make_request(). > > So it is interesting that the flush is getting inserted in the elevator > at all. AFAIK that shouldn't be (and historically hasn't been) the > case. > > Combination of onstack plug changes?
It is, it forces a sort insert. I'll fix this up, I'm relieved we have a good handle on this issue now.
-- Jens Axboe
| |