ceph: check PG_Private flag before accessing page->private
I got lots of NULL pointer dereference Oops when compiling kernel on ceph.
The bug is because the kernel page migration routine replaces some pages
in the page cache with new pages, these new pages' private can be non-zero.
Signed-off-by: Zheng Yan <zheng.z.yan@intel.com>
Signed-off-by: Sage Weil <sage@inktank.com>
diff --git a/fs/ceph/addr.c b/fs/ceph/addr.c
index 173b1d2..8b67304 100644
--- a/fs/ceph/addr.c
+++ b/fs/ceph/addr.c
@@ -54,7 +54,12 @@
(CONGESTION_ON_THRESH(congestion_kb) - \
(CONGESTION_ON_THRESH(congestion_kb) >> 2))
-
+static inline struct ceph_snap_context *page_snap_context(struct page *page)
+{
+ if (PagePrivate(page))
+ return (void *)page->private;
+ return NULL;
+}
/*
* Dirty a page. Optimistically adjust accounting, on the assumption
@@ -142,10 +147,9 @@
{
struct inode *inode;
struct ceph_inode_info *ci;
- struct ceph_snap_context *snapc = (void *)page->private;
+ struct ceph_snap_context *snapc = page_snap_context(page);
BUG_ON(!PageLocked(page));
- BUG_ON(!page->private);
BUG_ON(!PagePrivate(page));
BUG_ON(!page->mapping);
@@ -182,7 +186,6 @@
struct inode *inode = page->mapping ? page->mapping->host : NULL;
dout("%p releasepage %p idx %lu\n", inode, page, page->index);
WARN_ON(PageDirty(page));
- WARN_ON(page->private);
WARN_ON(PagePrivate(page));
return 0;
}
@@ -443,7 +446,7 @@
osdc = &fsc->client->osdc;
/* verify this is a writeable snap context */
- snapc = (void *)page->private;
+ snapc = page_snap_context(page);
if (snapc == NULL) {
dout("writepage %p page %p not dirty?\n", inode, page);
goto out;
@@ -451,7 +454,7 @@
oldest = get_oldest_context(inode, &snap_size);
if (snapc->seq > oldest->seq) {
dout("writepage %p page %p snapc %p not writeable - noop\n",
- inode, page, (void *)page->private);
+ inode, page, snapc);
/* we should only noop if called by kswapd */
WARN_ON((current->flags & PF_MEMALLOC) == 0);
ceph_put_snap_context(oldest);
@@ -591,7 +594,7 @@
clear_bdi_congested(&fsc->backing_dev_info,
BLK_RW_ASYNC);
- ceph_put_snap_context((void *)page->private);
+ ceph_put_snap_context(page_snap_context(page));
page->private = 0;
ClearPagePrivate(page);
dout("unlocking %d %p\n", i, page);
@@ -795,7 +798,7 @@
}
/* only if matching snap context */
- pgsnapc = (void *)page->private;
+ pgsnapc = page_snap_context(page);
if (pgsnapc->seq > snapc->seq) {
dout("page snapc %p %lld > oldest %p %lld\n",
pgsnapc, pgsnapc->seq, snapc, snapc->seq);
@@ -984,7 +987,7 @@
BUG_ON(!ci->i_snap_realm);
down_read(&mdsc->snap_rwsem);
BUG_ON(!ci->i_snap_realm->cached_context);
- snapc = (void *)page->private;
+ snapc = page_snap_context(page);
if (snapc && snapc != ci->i_head_snapc) {
/*
* this page is already dirty in another (older) snap