Re: [PATCH 1/1] mm: bdi: Initialize bdi_min_ratio when bdi unregister

[Andrew Morton <akpm@linux-foundation.org>]

On Thu, 21 Oct 2021 13:01:30 +0100 Matthew Wilcox <willy@infradead.org> wrote:

> On Thu, Oct 21, 2021 at 04:16:52AM -0700, Christoph Hellwig wrote:
> > On Fri, Oct 22, 2021 at 01:19:43AM +0900, Manjong Lee wrote:
> > > Because when sdcard is removed, bdi_min_ratio value will remain.
> > > Currently, the only way to reset bdi_ min_ratio is to reboot.
> > 
> > But bdis that are unregistered are never re-registered.  What is
> > the problem you're trying to solve?
> 
> The global bdi_min_ratio needs to be adjusted.  See
> bdi_set_min_ratio() in mm/page-writeback.c.

I added cc:stable to this and tweaked the comment & coding style a bit:

--- a/mm/backing-dev.c~mm-bdi-initialize-bdi_min_ratio-when-bdi-unregister-fix
+++ a/mm/backing-dev.c
@@ -947,10 +947,12 @@ void bdi_unregister(struct backing_dev_i
 	wb_shutdown(&bdi->wb);
 	cgwb_bdi_unregister(bdi);
 
-	/* if min ratio doesn't 0, it has to set 0 before unregister */
-	if (bdi->min_ratio) {
+	/*
+	 * 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);
_