[Ocfs2-devel] [PATCH 16/16] ocfs2: Fix ocfs2_page_mkwrite()
Sunil Mushran
sunil.mushran at oracle.com
Thu Jul 14 15:50:27 PDT 2011
From: Wengang Wang <wen.gang.wang at oracle.com>
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 at oracle.com>
Signed-off-by: Sunil Mushran <sunil.mushran at oracle.com>
---
fs/ocfs2/aops.c | 51 +++++++++++++++++++++++++++++++++++++++++++--------
fs/ocfs2/mmap.c | 53 ++++++++++++++++++++++++-----------------------------
2 files changed, 67 insertions(+), 37 deletions(-)
diff --git a/fs/ocfs2/aops.c b/fs/ocfs2/aops.c
index ac97bca..92e363b 100644
--- a/fs/ocfs2/aops.c
+++ b/fs/ocfs2/aops.c
@@ -865,6 +865,12 @@ struct ocfs2_write_ctxt {
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.
*/
@@ -897,6 +903,24 @@ void ocfs2_unlock_and_free_pages(struct page **pages, int num_pages)
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);
@@ -1134,20 +1158,17 @@ static int ocfs2_grab_pages_for_write(struct address_space *mapping,
*/
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);
@@ -1162,6 +1183,8 @@ static int ocfs2_grab_pages_for_write(struct address_space *mapping,
wc->w_target_page = wc->w_pages[i];
}
out:
+ if (ret)
+ wc->w_target_locked = false;
return ret;
}
@@ -1819,11 +1842,23 @@ try_again:
*/
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) {
diff --git a/fs/ocfs2/mmap.c b/fs/ocfs2/mmap.c
index 3e9393c..9cd4108 100644
--- a/fs/ocfs2/mmap.c
+++ b/fs/ocfs2/mmap.c
@@ -61,7 +61,7 @@ static int ocfs2_fault(struct vm_area_struct *area, struct vm_fault *vmf)
static int __ocfs2_page_mkwrite(struct file *file, struct buffer_head *di_bh,
struct page *page)
{
- int ret;
+ int ret = VM_FAULT_NOPAGE;
struct inode *inode = file->f_path.dentry->d_inode;
struct address_space *mapping = inode->i_mapping;
loff_t pos = page_offset(page);
@@ -71,32 +71,25 @@ static int __ocfs2_page_mkwrite(struct file *file, struct buffer_head *di_bh,
void *fsdata;
loff_t size = i_size_read(inode);
- /*
- * Another node might have truncated while we were waiting on
- * cluster locks.
- * We don't check size == 0 before the shift. This is borrowed
- * from do_generic_file_read.
- */
last_index = (size - 1) >> PAGE_CACHE_SHIFT;
- if (unlikely(!size || page->index > last_index)) {
- ret = -EINVAL;
- goto out;
- }
/*
- * The i_size check above doesn't catch the case where nodes
- * truncated and then re-extended the file. We'll re-check the
- * page mapping after taking the page lock inside of
- * ocfs2_write_begin_nolock().
+ * There are cases that lead to the page no longer bebongs to the
+ * mapping.
+ * 1) pagecache truncates locally due to memory pressure.
+ * 2) pagecache truncates when another is taking EX lock against
+ * inode lock. see ocfs2_data_convert_worker.
+ *
+ * The i_size check doesn't catch the case where nodes truncated and
+ * then re-extended the file. We'll re-check the page mapping after
+ * taking the page lock inside of ocfs2_write_begin_nolock().
+ *
+ * Let VM retry with these cases.
*/
- if (!PageUptodate(page) || page->mapping != inode->i_mapping) {
- /*
- * the page has been umapped in ocfs2_data_downconvert_worker.
- * So return 0 here and let VFS retry.
- */
- ret = 0;
+ if ((page->mapping != inode->i_mapping) ||
+ (!PageUptodate(page)) ||
+ (page_offset(page) >= size))
goto out;
- }
/*
* Call ocfs2_write_begin() and ocfs2_write_end() to take
@@ -116,17 +109,21 @@ static int __ocfs2_page_mkwrite(struct file *file, struct buffer_head *di_bh,
if (ret) {
if (ret != -ENOSPC)
mlog_errno(ret);
+ if (ret == -ENOMEM)
+ ret = VM_FAULT_OOM;
+ else
+ ret = VM_FAULT_SIGBUS;
goto out;
}
- ret = ocfs2_write_end_nolock(mapping, pos, len, len, locked_page,
- fsdata);
- if (ret < 0) {
- mlog_errno(ret);
+ if (!locked_page) {
+ ret = VM_FAULT_NOPAGE;
goto out;
}
+ ret = ocfs2_write_end_nolock(mapping, pos, len, len, locked_page,
+ fsdata);
BUG_ON(ret != len);
- ret = 0;
+ ret = VM_FAULT_LOCKED;
out:
return ret;
}
@@ -168,8 +165,6 @@ static int ocfs2_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
out:
ocfs2_unblock_signals(&oldset);
- if (ret)
- ret = VM_FAULT_SIGBUS;
return ret;
}
--
1.7.4.1
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