gfs2: Don't start unnecessary transactions during log flush

Commit 8d39197 ("gfs2: Remove __gfs2_writepage()") changed the log
flush code in gfs2_ail1_start_one() to call aops->writepages() instead
of aops->writepage().  For jdata inodes, this means that we will now try
to reserve log space and start a transaction before we can determine
that the pages in question have already been journaled.  When this
happens in the context of gfs2_logd(), it can now appear that not enough
log space is available for freeing up log space, and we will lock up.

Fix that by issuing journal writes directly instead of going through
aops->writepages() in the log flush code.

Fixes: 8d39197 ("gfs2: Remove __gfs2_writepage()")
Signed-off-by: Andreas Gruenbacher <[email protected]>

Author: Andreas Gruenbacher

fs/gfs2/aops.c

@@ -117,6 +117,37 @@ static int __gfs2_jdata_write_folio(struct folio *folio,
 	return gfs2_write_jdata_folio(folio, wbc);
 }
 
+/**
+ * gfs2_jdata_writeback - Write jdata folios to the log
+ * @mapping: The mapping to write
+ * @wbc: The writeback control
+ *
+ * Returns: errno
+ */
+int gfs2_jdata_writeback(struct address_space *mapping, struct writeback_control *wbc)
+{
+	struct inode *inode = mapping->host;
+	struct gfs2_inode *ip = GFS2_I(inode);
+	struct gfs2_sbd *sdp = GFS2_SB(mapping->host);
+	struct folio *folio = NULL;
+	int error;
+
+	BUG_ON(current->journal_info);
+	if (gfs2_assert_withdraw(sdp, ip->i_gl->gl_state == LM_ST_EXCLUSIVE))
+		return 0;
+
+	while ((folio = writeback_iter(mapping, wbc, folio, &error))) {
+		if (folio_test_checked(folio)) {
+			folio_redirty_for_writepage(wbc, folio);
+			folio_unlock(folio);
+			continue;
+		}
+		error = __gfs2_jdata_write_folio(folio, wbc);
+	}
+
+	return error;
+}
+
 /**
  * gfs2_writepages - Write a bunch of dirty pages back to disk
  * @mapping: The mapping to write

fs/gfs2/aops.h

@@ -9,5 +9,6 @@
 #include "incore.h"
 
 void adjust_fs_space(struct inode *inode);
+int gfs2_jdata_writeback(struct address_space *mapping, struct writeback_control *wbc);
 
 #endif /* __AOPS_DOT_H__ */

fs/gfs2/log.c

@@ -31,6 +31,7 @@
 #include "dir.h"
 #include "trace_gfs2.h"
 #include "trans.h"
+#include "aops.h"
 
 static void gfs2_log_shutdown(struct gfs2_sbd *sdp);
 
@@ -131,7 +132,11 @@ __acquires(&sdp->sd_ail_lock)
 		if (!mapping)
 			continue;
 		spin_unlock(&sdp->sd_ail_lock);
-		ret = mapping->a_ops->writepages(mapping, wbc);
+		BUG_ON(GFS2_SB(mapping->host) != sdp);
+		if (gfs2_is_jdata(GFS2_I(mapping->host)))
+			ret = gfs2_jdata_writeback(mapping, wbc);
+		else
+			ret = mapping->a_ops->writepages(mapping, wbc);
 		if (need_resched()) {
 			blk_finish_plug(plug);
 			cond_resched();