[patch 059/192] fs/proc/kcore: use page_offline_(freeze|thaw)

[Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>]

From: David Hildenbrand <david@xxxxxxxxxx>
Subject: fs/proc/kcore: use page_offline_(freeze|thaw)

Let's properly synchronize with drivers that set PageOffline(). 
Unfreeze/thaw every now and then, so drivers that want to set
PageOffline() can make progress.

Link: https://lkml.kernel.org/r/20210526093041.8800-7-david@xxxxxxxxxx
Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
Acked-by: Mike Rapoport <rppt@xxxxxxxxxxxxx>
Reviewed-by: Oscar Salvador <osalvador@xxxxxxx>
Cc: Aili Yao <yaoaili@xxxxxxxxxxxx>
Cc: Alexey Dobriyan <adobriyan@xxxxxxxxx>
Cc: Alex Shi <alex.shi@xxxxxxxxxxxxxxxxx>
Cc: Haiyang Zhang <haiyangz@xxxxxxxxxxxxx>
Cc: Jason Wang <jasowang@xxxxxxxxxx>
Cc: Jiri Bohac <jbohac@xxxxxxx>
Cc: "K. Y. Srinivasan" <kys@xxxxxxxxxxxxx>
Cc: "Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx>
Cc: "Michael S. Tsirkin" <mst@xxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Cc: Naoya Horiguchi <naoya.horiguchi@xxxxxxx>
Cc: Roman Gushchin <guro@xxxxxx>
Cc: Stephen Hemminger <sthemmin@xxxxxxxxxxxxx>
Cc: Steven Price <steven.price@xxxxxxx>
Cc: Wei Liu <wei.liu@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---

 fs/proc/kcore.c |   13 +++++++++++++
 1 file changed, 13 insertions(+)

--- a/fs/proc/kcore.c~fs-proc-kcore-use-page_offline_freezethaw
+++ a/fs/proc/kcore.c
@@ -313,6 +313,7 @@ read_kcore(struct file *file, char __use
 {
 	char *buf = file->private_data;
 	size_t phdrs_offset, notes_offset, data_offset;
+	size_t page_offline_frozen = 1;
 	size_t phdrs_len, notes_len;
 	struct kcore_list *m;
 	size_t tsz;
@@ -322,6 +323,11 @@ read_kcore(struct file *file, char __use
 	int ret = 0;
 
 	down_read(&kclist_lock);
+	/*
+	 * Don't race against drivers that set PageOffline() and expect no
+	 * further page access.
+	 */
+	page_offline_freeze();
 
 	get_kcore_size(&nphdr, &phdrs_len, &notes_len, &data_offset);
 	phdrs_offset = sizeof(struct elfhdr);
@@ -480,6 +486,12 @@ read_kcore(struct file *file, char __use
 			}
 		}
 
+		if (page_offline_frozen++ % MAX_ORDER_NR_PAGES == 0) {
+			page_offline_thaw();
+			cond_resched();
+			page_offline_freeze();
+		}
+
 		if (&m->list == &kclist_head) {
 			if (clear_user(buffer, tsz)) {
 				ret = -EFAULT;
@@ -565,6 +577,7 @@ skip:
 	}
 
 out:
+	page_offline_thaw();
 	up_read(&kclist_lock);
 	if (ret)
 		return ret;
_