[PATCH 13/29] xfs: make xfs_trans_alloc() support nowait semantics

[Hao Xu <hao.xu@xxxxxxxxx>]

From: Hao Xu <howeyxu@xxxxxxxxxxx>

There are locks in xfs_trans_alloc(), spot them and apply trylock logic.
Make them return -EAGAIN when it would block. To achieve this, add
nowait parameter for those functions in the path. Besides, add a generic
transaction flag XFS_TRANS_NOWAIT to deliver nowait info.

Signed-off-by: Hao Xu <howeyxu@xxxxxxxxxxx>
---
 fs/xfs/libxfs/xfs_shared.h |  2 ++
 fs/xfs/xfs_iops.c          |  3 ++-
 fs/xfs/xfs_trans.c         | 21 ++++++++++++++++++---
 3 files changed, 22 insertions(+), 4 deletions(-)

diff --git a/fs/xfs/libxfs/xfs_shared.h b/fs/xfs/libxfs/xfs_shared.h
index c4381388c0c1..0ba3d6f53405 100644
--- a/fs/xfs/libxfs/xfs_shared.h
+++ b/fs/xfs/libxfs/xfs_shared.h
@@ -83,6 +83,8 @@ void	xfs_log_get_max_trans_res(struct xfs_mount *mp,
  * made then this algorithm will eventually find all the space it needs.
  */
 #define XFS_TRANS_LOWMODE	0x100	/* allocate in low space mode */
+/* Transaction should follow nowait semantics */
+#define XFS_TRANS_NOWAIT		(1u << 9)
 
 /*
  * Field values for xfs_trans_mod_sb.
diff --git a/fs/xfs/xfs_iops.c b/fs/xfs/xfs_iops.c
index 5fa391083de9..47b4fd5f8f5c 100644
--- a/fs/xfs/xfs_iops.c
+++ b/fs/xfs/xfs_iops.c
@@ -1054,7 +1054,8 @@ xfs_vn_update_time(
 	if (nowait)
 		old_pflags = memalloc_noio_save();
 
-	error = xfs_trans_alloc(mp, &M_RES(mp)->tr_fsyncts, 0, 0, 0, &tp);
+	error = xfs_trans_alloc(mp, &M_RES(mp)->tr_fsyncts, 0, 0,
+				nowait ? XFS_TRANS_NOWAIT : 0, &tp);
 	if (error)
 		goto out;
 
diff --git a/fs/xfs/xfs_trans.c b/fs/xfs/xfs_trans.c
index 8c0bfc9a33b1..dbec685f4f4a 100644
--- a/fs/xfs/xfs_trans.c
+++ b/fs/xfs/xfs_trans.c
@@ -251,6 +251,9 @@ xfs_trans_alloc(
 	struct xfs_trans	*tp;
 	bool			want_retry = true;
 	int			error;
+	bool			nowait = flags & XFS_TRANS_NOWAIT;
+	gfp_t			gfp_flags = GFP_KERNEL |
+					    (nowait ? 0 : __GFP_NOFAIL);
 
 	/*
 	 * Allocate the handle before we do our freeze accounting and setting up
@@ -258,9 +261,21 @@ xfs_trans_alloc(
 	 * by doing GFP_KERNEL allocations inside sb_start_intwrite().
 	 */
 retry:
-	tp = kmem_cache_zalloc(xfs_trans_cache, GFP_KERNEL | __GFP_NOFAIL);
-	if (!(flags & XFS_TRANS_NO_WRITECOUNT))
-		sb_start_intwrite(mp->m_super);
+	tp = kmem_cache_zalloc(xfs_trans_cache, gfp_flags);
+	if (!tp)
+		return -EAGAIN;
+	if (!(flags & XFS_TRANS_NO_WRITECOUNT)) {
+		if (nowait) {
+			bool locked = sb_start_intwrite_trylock(mp->m_super);
+
+			if (!locked) {
+				xfs_trans_cancel(tp);
+				return -EAGAIN;
+			}
+		} else {
+			sb_start_intwrite(mp->m_super);
+		}
+	}
 	xfs_trans_set_context(tp);
 
 	/*
-- 
2.25.1