[PATCH 4.14 13/53] mm: bdi: initialize bdi_min_ratio when bdi is unregistered

[Greg Kroah-Hartman]

From: Manjong Lee <mj0123.lee@xxxxxxxxxxx>

commit 3c376dfafbf7a8ea0dea212d095ddd83e93280bb upstream.

Initialize min_ratio if it is set during bdi unregistration.  This can
prevent problems that may occur a when bdi is removed without resetting
min_ratio.

For example.
1) insert external sdcard
2) set external sdcard's min_ratio 70
3) remove external sdcard without setting min_ratio 0
4) insert external sdcard
5) set external sdcard's min_ratio 70 << error occur(can't set)

Because when an sdcard is removed, the present bdi_min_ratio value will
remain.  Currently, the only way to reset bdi_min_ratio is to reboot.

[akpm@xxxxxxxxxxxxxxxxxxxx: tweak comment and coding style]

Link: https://lkml.kernel.org/r/20211021161942.5983-1-mj0123.lee@xxxxxxxxxxx
Signed-off-by: Manjong Lee <mj0123.lee@xxxxxxxxxxx>
Acked-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Cc: Changheun Lee <nanich.lee@xxxxxxxxxxx>
Cc: Jens Axboe <axboe@xxxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: <seunghwan.hyun@xxxxxxxxxxx>
Cc: <sookwan7.kim@xxxxxxxxxxx>
Cc: <yt0928.kim@xxxxxxxxxxx>
Cc: <junho89.kim@xxxxxxxxxxx>
Cc: <jisoo2146.oh@xxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 mm/backing-dev.c |    7 +++++++
 1 file changed, 7 insertions(+)

--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -942,6 +942,13 @@ void bdi_unregister(struct backing_dev_i
 	wb_shutdown(&bdi->wb);
 	cgwb_bdi_unregister(bdi);
 
+	/*
+	 * If this BDI's min ratio has been set, use bdi_set_min_ratio() to
+	 * update the global bdi_min_ratio.
+	 */
+	if (bdi->min_ratio)
+		bdi_set_min_ratio(bdi, 0);
+
 	if (bdi->dev) {
 		bdi_debug_unregister(bdi);
 		device_unregister(bdi->dev);