[PATCH v2 6/6] fs/proc/kcore: use page_offline_(freeze|thaw)

[David Hildenbrand]

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 <da...@redhat.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

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