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authorTejun Heo <tj@kernel.org>2015-09-08 19:20:22 +0300
committerJens Axboe <axboe@fb.com>2015-10-15 18:53:28 +0300
commitb02176f30cd30acccd3b633ab7d9aed8b5da52ff (patch)
tree96861c4612e0aae3b020c2293d05b7afb67f2557 /mm
parent81c04b943872e0332872df18cec1dec89b178b4d (diff)
downloadlinux-b02176f30cd30acccd3b633ab7d9aed8b5da52ff.tar.xz
block: don't release bdi while request_queue has live references
bdi's are initialized in two steps, bdi_init() and bdi_register(), but destroyed in a single step by bdi_destroy() which, for a bdi embedded in a request_queue, is called during blk_cleanup_queue() which makes the queue invisible and starts the draining of remaining usages. A request_queue's user can access the congestion state of the embedded bdi as long as it holds a reference to the queue. As such, it may access the congested state of a queue which finished blk_cleanup_queue() but hasn't reached blk_release_queue() yet. Because the congested state was embedded in backing_dev_info which in turn is embedded in request_queue, accessing the congested state after bdi_destroy() was called was fine. The bdi was destroyed but the memory region for the congested state remained accessible till the queue got released. a13f35e87140 ("writeback: don't embed root bdi_writeback_congested in bdi_writeback") changed the situation. Now, the root congested state which is expected to be pinned while request_queue remains accessible is separately reference counted and the base ref is put during bdi_destroy(). This means that the root congested state may go away prematurely while the queue is between bdi_dstroy() and blk_cleanup_queue(), which was detected by Andrey's KASAN tests. The root cause of this problem is that bdi doesn't distinguish the two steps of destruction, unregistration and release, and now the root congested state actually requires a separate release step. To fix the issue, this patch separates out bdi_unregister() and bdi_exit() from bdi_destroy(). bdi_unregister() is called from blk_cleanup_queue() and bdi_exit() from blk_release_queue(). bdi_destroy() is now just a simple wrapper calling the two steps back-to-back. While at it, the prototype of bdi_destroy() is moved right below bdi_setup_and_register() so that the counterpart operations are located together. Signed-off-by: Tejun Heo <tj@kernel.org> Fixes: a13f35e87140 ("writeback: don't embed root bdi_writeback_congested in bdi_writeback") Cc: stable@vger.kernel.org # v4.2+ Reported-and-tested-by: Andrey Konovalov <andreyknvl@google.com> Link: http://lkml.kernel.org/g/CAAeHK+zUJ74Zn17=rOyxacHU18SgCfC6bsYW=6kCY5GXJBwGfQ@mail.gmail.com Reviewed-by: Jan Kara <jack@suse.com> Reviewed-by: Jeff Moyer <jmoyer@redhat.com> Signed-off-by: Jens Axboe <axboe@fb.com>
Diffstat (limited to 'mm')
-rw-r--r--mm/backing-dev.c12
1 files changed, 11 insertions, 1 deletions
diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index e92d77937fd3..9e841399041a 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -835,7 +835,7 @@ static void bdi_remove_from_list(struct backing_dev_info *bdi)
synchronize_rcu_expedited();
}
-void bdi_destroy(struct backing_dev_info *bdi)
+void bdi_unregister(struct backing_dev_info *bdi)
{
/* make sure nobody finds us on the bdi_list anymore */
bdi_remove_from_list(bdi);
@@ -847,9 +847,19 @@ void bdi_destroy(struct backing_dev_info *bdi)
device_unregister(bdi->dev);
bdi->dev = NULL;
}
+}
+void bdi_exit(struct backing_dev_info *bdi)
+{
+ WARN_ON_ONCE(bdi->dev);
wb_exit(&bdi->wb);
}
+
+void bdi_destroy(struct backing_dev_info *bdi)
+{
+ bdi_unregister(bdi);
+ bdi_exit(bdi);
+}
EXPORT_SYMBOL(bdi_destroy);
/*