linux-kernel - [PATCH 5.10 044/132] mm: bdi: initialize bdi_min

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Date:   Mon, 13 Dec 2021 10:29:45 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Manjong Lee <mj0123.lee@...sung.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Changheun Lee <nanich.lee@...sung.com>,
        Jens Axboe <axboe@...nel.dk>,
        Christoph Hellwig <hch@...radead.org>,
        Matthew Wilcox <willy@...radead.org>,
        seunghwan.hyun@...sung.com, sookwan7.kim@...sung.com,
        yt0928.kim@...sung.com, junho89.kim@...sung.com,
        jisoo2146.oh@...sung.com,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH 5.10 044/132] mm: bdi: initialize bdi_min_ratio when bdi is unregistered

From: Manjong Lee <mj0123.lee@...sung.com>

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@...ux-foundation.org: tweak comment and coding style]

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

--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -872,6 +872,13 @@ 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);