From 9f83e45eb54fc7198dc59fc63255341851ba4c48 Mon Sep 17 00:00:00 2001 From: Oleg Nesterov Date: Mon, 21 Aug 2006 08:34:15 +0200 Subject: [PATCH] [PATCH] Fix current_io_context() vs set_task_ioprio() race 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 Signed-off-by: Jens Axboe --- block/ll_rw_blk.c | 2 ++ fs/ioprio.c | 3 +++ 2 files changed, 5 insertions(+) diff --git a/block/ll_rw_blk.c b/block/ll_rw_blk.c index 61d6b3c65b6..ddd9253f9d5 100644 --- a/block/ll_rw_blk.c +++ b/block/ll_rw_blk.c @@ -3628,6 +3628,8 @@ struct io_context *current_io_context(gfp_t gfp_flags) 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; } diff --git a/fs/ioprio.c b/fs/ioprio.c index 3db31038e9a..06578311c63 100644 --- a/fs/ioprio.c +++ b/fs/ioprio.c @@ -44,6 +44,9 @@ static int set_task_ioprio(struct task_struct *task, int ioprio) 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);