This patch checks for and prevents the deadlock with a page in
journalled writeback in __ext4_journalled_writepage().
It turns out that __ext4_journalled_writepage() may race with itself
in another task (e.g., two tasks set the same mmap'ed page dirty and
called msync(), one after the other), so we have to check/handle it.
Signed-off-by: Mauricio Faria de Oliveira <mfo@xxxxxxxxxxxxx>
---
fs/ext4/inode.c | 16 +++++++++++++++-
1 file changed, 15 insertions(+), 1 deletion(-)
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 574a062b8bcd..401313be8a5b 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -1910,6 +1910,7 @@ static noinline int __ext4_journalled_writepage(struct page *page,
*/
ejwp = kmem_cache_alloc(ext4_journalled_wb_page_cachep, GFP_KERNEL);
+retry_journal:
handle = ext4_journal_start(inode, EXT4_HT_WRITE_PAGE,
ext4_writepage_trans_blocks(inode));
if (IS_ERR(handle)) {
@@ -1948,7 +1949,20 @@ static noinline int __ext4_journalled_writepage(struct page *page,
goto out;
}
- /* Data integrity writeback; have to wait and do it. */
+ /*
+ * Data integrity writeback; have to wait and do it.
+ *
+ * Check for deadlock with page in journalled writeback
+ * (i.e. another task running/ran this function as well)
+ */
+ if (ext4_check_journalled_writeback(handle, page)) {
+ get_page(page);
+ unlock_page(page);
+ ext4_journal_stop(handle);
+ ext4_start_commit_datasync(inode);
+ wait_on_page_writeback(page);
+ goto retry_journal;
+ }
wait_on_page_writeback(page);
}
--
2.20.1
