[PATCH v1 7/7] fs/proc/kcore: use page_offline_(freeze|unfreeze)

David Hildenbrand
2021-04-29T12:27:40Z

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