Messages in this thread | | | Date | Mon, 21 Aug 2006 08:28:54 +0200 | From | Jens Axboe <> | Subject | Re: [PATCH] fix? current_io_context() vs set_task_ioprio() race |
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On Sun, Aug 20 2006, Oleg Nesterov wrote: > I know nothing about io scheduler, but I suspect set_task_ioprio() is not safe. > > current_io_context() initializes "struct io_context", then sets ->io_context. > set_task_ioprio() running on another cpu may see the changes out of order, so > ->set_ioprio(ioc) may use io_context which was not initialized properly. > > Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru> > > --- 2.6.18-rc4/block/ll_rw_blk.c~3_race 2006-07-16 01:53:08.000000000 +0400 > +++ 2.6.18-rc4/block/ll_rw_blk.c 2006-08-20 19:30:10.000000000 +0400 > @@ -3628,6 +3628,8 @@ struct io_context *current_io_context(gf > ret->nr_batch_requests = 0; /* because this is 0 */ > ret->aic = NULL; > ret->cic_root.rb_node = NULL; > + /* make sure set_task_ioprio() sees the settings above */ > + smp_wmb(); > tsk->io_context = ret; > } > > --- 2.6.18-rc4/fs/ioprio.c~3_race 2006-08-20 19:09:08.000000000 +0400 > +++ 2.6.18-rc4/fs/ioprio.c 2006-08-20 19:57:14.000000000 +0400 > @@ -44,6 +44,9 @@ static int set_task_ioprio(struct task_s > task->ioprio = ioprio; > > ioc = task->io_context; > + /* see wmb() in current_io_context() */ > + smp_read_barrier_depends(); > + > if (ioc && ioc->set_ioprio) > ioc->set_ioprio(ioc, ioprio);
Agree, applied.
-- Jens Axboe
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