[PATCH] gfs2: do not evict glocks with populated address spaces

[Guilherme Giacomo Simoes <trintaeoitogc@gmail.com>]

Metadata glocks may have associated address spaces used as caches. Avoid
reclaiming such glocks under memory pressure while their mappings are
still populated or their state is not unlocked, as this can lead to
invalid page cache state and GLOCK_BUG_ON().

Signed-off-by: Guilherme Giacomo Simoes <trintaeoitogc@gmail.com>
---
 fs/gfs2/glock.h | 30 ++++++++++++++++++++++++++++++
 fs/gfs2/super.c |  3 +++
 2 files changed, 33 insertions(+)

diff --git a/fs/gfs2/glock.h b/fs/gfs2/glock.h
index 55d5985f32a0..12f57461f687 100644
--- a/fs/gfs2/glock.h
+++ b/fs/gfs2/glock.h
@@ -305,4 +305,34 @@ static inline bool glock_needs_demote(struct gfs2_glock *gl)
 		test_bit(GLF_PENDING_DEMOTE, &gl->gl_flags));
 }
 
+/*
+ * gfs2_glock_not_evictable - check if a glock is not evictable
+ * @gl:	The glock to check
+ *
+ * Glocks which do not represent normal filesystem inodes (e.g. statfs, quota, rindex)
+ * may have associated address spaces used as metadata caches. These glocks must not
+ * be reclaimed under memory pressure while their mappings are still populated or their
+ * state is not unlocked.
+ */
+
+static inline bool gfs2_glock_not_evictable(struct gfs2_glock *gl)
+{
+	if (gl->gl_name.ln_type == LM_TYPE_INODE)
+		return false;
+
+	if (gl->gl_ops->go_flags & GLOF_ASPACE) {
+		struct gfs2_glock_aspace *gla;
+
+		gla = container_of(gl, struct gfs2_glock_aspace, glock);
+
+		if (!mapping_empty(&gla->mapping))
+			return true;
+	}
+
+	if (gl->gl_state != LM_ST_UNLOCKED)
+		return true;
+
+	return false;
+}
+
 #endif /* __GLOCK_DOT_H__ */
diff --git a/fs/gfs2/super.c b/fs/gfs2/super.c
index f6cd907b3ec6..86544cdafe53 100644
--- a/fs/gfs2/super.c
+++ b/fs/gfs2/super.c
@@ -1164,6 +1164,9 @@ static int gfs2_show_options(struct seq_file *s, struct dentry *root)
 
 static void gfs2_glock_put_eventually(struct gfs2_glock *gl)
 {
+	if (gfs2_glock_not_evictable(gl))
+		return;
+
 	if (current->flags & PF_MEMALLOC)
 		gfs2_glock_put_async(gl);
 	else
-- 
2.34.1