[PATCH v5 08/24] fsverity: add per-sb workqueue for post read processing

[Andrey Albershteyn <aalbersh@redhat.com>]

For XFS, fsverity's global workqueue is not really suitable due to:

1. High priority workqueues are used within XFS to ensure that data
   IO completion cannot stall processing of journal IO completions.
   Hence using a WQ_HIGHPRI workqueue directly in the user data IO
   path is a potential filesystem livelock/deadlock vector.

2. The fsverity workqueue is global - it creates a cross-filesystem
   contention point.

This patch adds per-filesystem, per-cpu workqueue for fsverity
work. This allows iomap to add verification work in the read path on
BIO completion.

Signed-off-by: Andrey Albershteyn <aalbersh@redhat.com>
---
 fs/super.c               |  7 +++++++
 include/linux/fs.h       |  2 ++
 include/linux/fsverity.h | 22 ++++++++++++++++++++++
 3 files changed, 31 insertions(+)

diff --git a/fs/super.c b/fs/super.c
index d6efeba0d0ce..03795ee4d9b9 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -637,6 +637,13 @@ void generic_shutdown_super(struct super_block *sb)
 			sb->s_dio_done_wq = NULL;
 		}
 
+#ifdef CONFIG_FS_VERITY
+		if (sb->s_read_done_wq) {
+			destroy_workqueue(sb->s_read_done_wq);
+			sb->s_read_done_wq = NULL;
+		}
+#endif
+
 		if (sop->put_super)
 			sop->put_super(sb);
 
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 1fbc72c5f112..5863519ffd51 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1223,6 +1223,8 @@ struct super_block {
 #endif
 #ifdef CONFIG_FS_VERITY
 	const struct fsverity_operations *s_vop;
+	/* Completion queue for post read verification */
+	struct workqueue_struct *s_read_done_wq;
 #endif
 #if IS_ENABLED(CONFIG_UNICODE)
 	struct unicode_map *s_encoding;
diff --git a/include/linux/fsverity.h b/include/linux/fsverity.h
index 0973b521ac5a..45b7c613148a 100644
--- a/include/linux/fsverity.h
+++ b/include/linux/fsverity.h
@@ -241,6 +241,22 @@ void fsverity_enqueue_verify_work(struct work_struct *work);
 void fsverity_invalidate_block(struct inode *inode,
 		struct fsverity_blockbuf *block);
 
+static inline int fsverity_set_ops(struct super_block *sb,
+				   const struct fsverity_operations *ops)
+{
+	sb->s_vop = ops;
+
+	/* Create per-sb workqueue for post read bio verification */
+	struct workqueue_struct *wq = alloc_workqueue(
+		"pread/%s", (WQ_FREEZABLE | WQ_MEM_RECLAIM), 0, sb->s_id);
+	if (!wq)
+		return -ENOMEM;
+
+	sb->s_read_done_wq = wq;
+
+	return 0;
+}
+
 #else /* !CONFIG_FS_VERITY */
 
 static inline struct fsverity_info *fsverity_get_info(const struct inode *inode)
@@ -318,6 +334,12 @@ static inline void fsverity_enqueue_verify_work(struct work_struct *work)
 	WARN_ON_ONCE(1);
 }
 
+static inline int fsverity_set_ops(struct super_block *sb,
+				   const struct fsverity_operations *ops)
+{
+	return -EOPNOTSUPP;
+}
+
 #endif	/* !CONFIG_FS_VERITY */
 
 static inline bool fsverity_verify_folio(struct folio *folio)
-- 
2.42.0