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From:   David Hildenbrand <david@redhat.com>
To:     linux-kernel@vger.kernel.org
Cc:     David Hildenbrand <david@redhat.com>,
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Subject: [PATCH v1 7/7] fs/proc/kcore: use page_offline_(freeze|unfreeze)
Date:   Thu, 29 Apr 2021 14:25:19 +0200
Message-Id: <20210429122519.15183-8-david@redhat.com>
In-Reply-To: <20210429122519.15183-1-david@redhat.com>
References: <20210429122519.15183-1-david@redhat.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

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

Signed-off-by: David Hildenbrand <david@redhat.com>
---
 fs/proc/kcore.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/fs/proc/kcore.c b/fs/proc/kcore.c
index 92ff1e4436cb..3d7531f47389 100644
--- a/fs/proc/kcore.c
+++ b/fs/proc/kcore.c
@@ -311,6 +311,7 @@ static void append_kcore_note(char *notes, size_t *i, const char *name,
 static ssize_t
 read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos)
 {
+	size_t page_offline_frozen = 0;
 	char *buf = file->private_data;
 	size_t phdrs_offset, notes_offset, data_offset;
 	size_t phdrs_len, notes_len;
@@ -509,6 +510,18 @@ read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos)
 			pfn = __pa(start) >> PAGE_SHIFT;
 			page = pfn_to_online_page(pfn);
 
+			/*
+			 * Don't race against drivers that set PageOffline()
+			 * and expect no further page access.
+			 */
+			if (page_offline_frozen == MAX_ORDER_NR_PAGES) {
+				page_offline_unfreeze();
+				page_offline_frozen = 0;
+				cond_resched();
+			}
+			if (!page_offline_frozen++)
+				page_offline_freeze();
+
 			/*
 			 * Don't read offline sections, logically offline pages
 			 * (e.g., inflated in a balloon), hwpoisoned pages,
@@ -565,6 +578,8 @@ read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos)
 	}
 
 out:
+	if (page_offline_frozen)
+		page_offline_unfreeze();
 	up_read(&kclist_lock);
 	if (ret)
 		return ret;
-- 
2.30.2