Messages in this thread |  | | | Date | Fri, 25 Mar 2011 11:40:46 -0400 | | From | Mike Snitzer <> | | Subject | Re: elevator private data for REQ_FLUSH |
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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?
1 [ 78.982169] Call Trace: 2 [ 78.982178] [<ffffffff8122d1fe>] cfq_insert_request+0x4e/0x47d 3 [ 78.982184] [<ffffffff8123e139>] ? do_raw_spin_lock+0x6b/0x122 4 [ 78.982189] [<ffffffff81218c4a>] elv_insert+0x212/0x265 5 [ 78.982192] [<ffffffff81218ced>] __elv_add_request+0x50/0x52 6 [ 78.982195] [<ffffffff8121b44a>] flush_plug_list+0xce/0x12f 7 [ 78.982199] [<ffffffff8121b4c0>] __blk_flush_plug+0x15/0x21 8 [ 78.982205] [<ffffffff8146b321>] schedule+0x43e/0xbea Mike
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