linux-kernel - [PATCH v2 6/6] fs/proc/kcore: use page_offline

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Message-Id: <20210514172247.176750-7-david@redhat.com>
Date:   Fri, 14 May 2021 19:22:47 +0200
From:   David Hildenbrand <david@...hat.com>
To:     linux-kernel@...r.kernel.org
Cc:     David Hildenbrand <david@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Mike Rapoport <rppt@...nel.org>,
        "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        Oscar Salvador <osalvador@...e.de>,
        Michal Hocko <mhocko@...e.com>, Roman Gushchin <guro@...com>,
        Alex Shi <alex.shi@...ux.alibaba.com>,
        Steven Price <steven.price@....com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Aili Yao <yaoaili@...gsoft.com>, Jiri Bohac <jbohac@...e.cz>,
        "K. Y. Srinivasan" <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Wei Liu <wei.liu@...nel.org>,
        Naoya Horiguchi <naoya.horiguchi@....com>,
        linux-hyperv@...r.kernel.org,
        virtualization@...ts.linux-foundation.org,
        linux-fsdevel@...r.kernel.org, linux-mm@...ck.org
Subject: [PATCH v2 6/6] 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.

Signed-off-by: David Hildenbrand <david@...hat.com>
---
 fs/proc/kcore.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/fs/proc/kcore.c b/fs/proc/kcore.c
index 92ff1e4436cb..982e694aae77 100644
--- a/fs/proc/kcore.c
+++ b/fs/proc/kcore.c
@@ -313,6 +313,7 @@ read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos)
 {
 	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 __user *buffer, size_t buflen, loff_t *fpos)
 	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 __user *buffer, size_t buflen, loff_t *fpos)
 			}
 		}
 
+		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 @@ read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos)
 	}
 
 out:
+	page_offline_thaw();
 	up_read(&kclist_lock);
 	if (ret)
 		return ret;
-- 
2.31.1