[PATCH] Fix current_io_context() vs set_task_ioprio() race (9f83e45e) · Commits · 戴 / test

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> Signed-off-by:

Jens Axboe <axboe@suse.de>

block/ll_rw_blk.c

+2 −0

Original line number	Diff line number	Diff line
		@@ -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;
		}

fs/ioprio.c

+3 −0

Original line number	Diff line number	Diff line
		@@ -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);

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