ocfs2: Fix ocfs2_page_mkwrite()
This patch address two shortcomings in ocfs2_page_mkwrite():
1. Makes the function return better VM_FAULT_* errors.
2. It handles a error that is triggered when a page is dropped from the mapping
due to memory pressure. This patch locks the page to prevent that.
[Patch was cleaned up by Sunil Mushran.]
Signed-off-by: Wengang Wang <wen.gang.wang@oracle.com>
Signed-off-by: Sunil Mushran <sunil.mushran@oracle.com>
diff --git a/fs/ocfs2/aops.c b/fs/ocfs2/aops.c
index c1efe93..ff98c16 100644
--- a/fs/ocfs2/aops.c
+++ b/fs/ocfs2/aops.c
@@ -863,6 +863,12 @@
struct page *w_target_page;
/*
+ * w_target_locked is used for page_mkwrite path indicating no unlocking
+ * against w_target_page in ocfs2_write_end_nolock.
+ */
+ unsigned int w_target_locked:1;
+
+ /*
* ocfs2_write_end() uses this to know what the real range to
* write in the target should be.
*/
@@ -895,6 +901,24 @@
static void ocfs2_free_write_ctxt(struct ocfs2_write_ctxt *wc)
{
+ int i;
+
+ /*
+ * w_target_locked is only set to true in the page_mkwrite() case.
+ * The intent is to allow us to lock the target page from write_begin()
+ * to write_end(). The caller must hold a ref on w_target_page.
+ */
+ if (wc->w_target_locked) {
+ BUG_ON(!wc->w_target_page);
+ for (i = 0; i < wc->w_num_pages; i++) {
+ if (wc->w_target_page == wc->w_pages[i]) {
+ wc->w_pages[i] = NULL;
+ break;
+ }
+ }
+ mark_page_accessed(wc->w_target_page);
+ page_cache_release(wc->w_target_page);
+ }
ocfs2_unlock_and_free_pages(wc->w_pages, wc->w_num_pages);
brelse(wc->w_di_bh);
@@ -1132,20 +1156,17 @@
*/
lock_page(mmap_page);
+ /* Exit and let the caller retry */
if (mmap_page->mapping != mapping) {
+ WARN_ON(mmap_page->mapping);
unlock_page(mmap_page);
- /*
- * Sanity check - the locking in
- * ocfs2_pagemkwrite() should ensure
- * that this code doesn't trigger.
- */
- ret = -EINVAL;
- mlog_errno(ret);
+ ret = -EAGAIN;
goto out;
}
page_cache_get(mmap_page);
wc->w_pages[i] = mmap_page;
+ wc->w_target_locked = true;
} else {
wc->w_pages[i] = find_or_create_page(mapping, index,
GFP_NOFS);
@@ -1160,6 +1181,8 @@
wc->w_target_page = wc->w_pages[i];
}
out:
+ if (ret)
+ wc->w_target_locked = false;
return ret;
}
@@ -1817,11 +1840,23 @@
*/
ret = ocfs2_grab_pages_for_write(mapping, wc, wc->w_cpos, pos, len,
cluster_of_pages, mmap_page);
- if (ret) {
+ if (ret && ret != -EAGAIN) {
mlog_errno(ret);
goto out_quota;
}
+ /*
+ * ocfs2_grab_pages_for_write() returns -EAGAIN if it could not lock
+ * the target page. In this case, we exit with no error and no target
+ * page. This will trigger the caller, page_mkwrite(), to re-try
+ * the operation.
+ */
+ if (ret == -EAGAIN) {
+ BUG_ON(wc->w_target_page);
+ ret = 0;
+ goto out_quota;
+ }
+
ret = ocfs2_write_cluster_by_desc(mapping, data_ac, meta_ac, wc, pos,
len);
if (ret) {