ext4: warn if direct reclaim tries to writeback pages

Direct reclaim should never writeback pages.  Warn if an attempt is made.

Signed-off-by: Mel Gorman <mgorman@suse.de>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Johannes Weiner <jweiner@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Minchan Kim <minchan.kim@gmail.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Alex Elder <aelder@sgi.com>
Cc: Theodore Ts'o <tytso@mit.edu>
Cc: Chris Mason <chris.mason@oracle.com>
Cc: Dave Hansen <dave@linux.vnet.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 5 insertions, 1 deletions

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 986e2388f031..0defe0bfe019 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -1811,8 +1811,12 @@ static int ext4_writepage(struct page *page,
                  * We don't want to do block allocation, so redirty
                  * the page and return.  We may reach here when we do
                  * a journal commit via journal_submit_inode_data_buffers.
-                 * We can also reach here via shrink_page_list
+                 * We can also reach here via shrink_page_list but it
+                 * should never be for direct reclaim so warn if that
+                 * happens
                  */
+                WARN_ON_ONCE((current->flags & (PF_MEMALLOC|PF_KSWAPD)) ==
+                                                                PF_MEMALLOC);
                 goto redirty_page;
         }
         if (commit_write)