From: Oleg Nesterov <oleg@tv-sign.ru>
Date: Mon, 21 Aug 2006 06:34:15 +0000 (+0200)
Subject: [PATCH] Fix current_io_context() vs set_task_ioprio() race
X-Git-Tag: v2.6.18-rc5~74^2~2
X-Git-Url: https://err.no/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=9f83e45eb54fc7198dc59fc63255341851ba4c48;p=linux-2.6

[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 <oleg@tv-sign.ru>
Signed-off-by: Jens Axboe <axboe@suse.de>
---

diff --git a/block/ll_rw_blk.c b/block/ll_rw_blk.c
index 61d6b3c65b..ddd9253f9d 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 3db31038e9..06578311c6 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);