[PATCH v4 13/25] xfs: introduce workqueue for post read IO work

[Andrey Albershteyn <aalbersh@xxxxxxxxxx>]

As noted by Dave there are two problems with using fs-verity's
workqueue in XFS:

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.

Signed-off-by: Andrey Albershteyn <aalbersh@xxxxxxxxxx>
---
 fs/xfs/xfs_aops.c  | 15 +++++++++++++--
 fs/xfs/xfs_linux.h |  1 +
 fs/xfs/xfs_mount.h |  1 +
 fs/xfs/xfs_super.c |  9 +++++++++
 4 files changed, 24 insertions(+), 2 deletions(-)

diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c
index 7a6627404160..70e444c151b2 100644
--- a/fs/xfs/xfs_aops.c
+++ b/fs/xfs/xfs_aops.c
@@ -548,19 +548,30 @@ xfs_vm_bmap(
 	return iomap_bmap(mapping, block, &xfs_read_iomap_ops);
 }
 
+static inline struct workqueue_struct *
+xfs_fsverity_wq(
+	struct address_space	*mapping)
+{
+	if (fsverity_active(mapping->host))
+		return XFS_I(mapping->host)->i_mount->m_postread_workqueue;
+	return NULL;
+}
+
 STATIC int
 xfs_vm_read_folio(
 	struct file		*unused,
 	struct folio		*folio)
 {
-	return iomap_read_folio(folio, &xfs_read_iomap_ops, NULL);
+	return iomap_read_folio(folio, &xfs_read_iomap_ops,
+				xfs_fsverity_wq(folio->mapping));
 }
 
 STATIC void
 xfs_vm_readahead(
 	struct readahead_control	*rac)
 {
-	iomap_readahead(rac, &xfs_read_iomap_ops, NULL);
+	iomap_readahead(rac, &xfs_read_iomap_ops,
+			xfs_fsverity_wq(rac->mapping));
 }
 
 static int
diff --git a/fs/xfs/xfs_linux.h b/fs/xfs/xfs_linux.h
index d7873e0360f0..9c76e025b5d8 100644
--- a/fs/xfs/xfs_linux.h
+++ b/fs/xfs/xfs_linux.h
@@ -64,6 +64,7 @@ typedef __u32			xfs_nlink_t;
 #include <linux/xattr.h>
 #include <linux/mnt_idmapping.h>
 #include <linux/debugfs.h>
+#include <linux/fsverity.h>
 
 #include <asm/page.h>
 #include <asm/div64.h>
diff --git a/fs/xfs/xfs_mount.h b/fs/xfs/xfs_mount.h
index 503fe3c7edbf..f64bf75f50d6 100644
--- a/fs/xfs/xfs_mount.h
+++ b/fs/xfs/xfs_mount.h
@@ -109,6 +109,7 @@ typedef struct xfs_mount {
 	struct xfs_mru_cache	*m_filestream;  /* per-mount filestream data */
 	struct workqueue_struct *m_buf_workqueue;
 	struct workqueue_struct	*m_unwritten_workqueue;
+	struct workqueue_struct	*m_postread_workqueue;
 	struct workqueue_struct	*m_reclaim_workqueue;
 	struct workqueue_struct	*m_sync_workqueue;
 	struct workqueue_struct *m_blockgc_wq;
diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
index 5a2512d20bd0..b2b6c1f24c42 100644
--- a/fs/xfs/xfs_super.c
+++ b/fs/xfs/xfs_super.c
@@ -553,6 +553,12 @@ xfs_init_mount_workqueues(
 	if (!mp->m_unwritten_workqueue)
 		goto out_destroy_buf;
 
+	mp->m_postread_workqueue = alloc_workqueue("xfs-pread/%s",
+			XFS_WQFLAGS(WQ_FREEZABLE | WQ_MEM_RECLAIM),
+			0, mp->m_super->s_id);
+	if (!mp->m_postread_workqueue)
+		goto out_destroy_postread;
+
 	mp->m_reclaim_workqueue = alloc_workqueue("xfs-reclaim/%s",
 			XFS_WQFLAGS(WQ_FREEZABLE | WQ_MEM_RECLAIM),
 			0, mp->m_super->s_id);
@@ -586,6 +592,8 @@ xfs_init_mount_workqueues(
 	destroy_workqueue(mp->m_reclaim_workqueue);
 out_destroy_unwritten:
 	destroy_workqueue(mp->m_unwritten_workqueue);
+out_destroy_postread:
+	destroy_workqueue(mp->m_postread_workqueue);
 out_destroy_buf:
 	destroy_workqueue(mp->m_buf_workqueue);
 out:
@@ -601,6 +609,7 @@ xfs_destroy_mount_workqueues(
 	destroy_workqueue(mp->m_inodegc_wq);
 	destroy_workqueue(mp->m_reclaim_workqueue);
 	destroy_workqueue(mp->m_unwritten_workqueue);
+	destroy_workqueue(mp->m_postread_workqueue);
 	destroy_workqueue(mp->m_buf_workqueue);
 }
 
-- 
2.42.0