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[26/29] xfs: return -EAGAIN when nowait meets sync in transaction commit

Message ID 20230825135431.1317785-27-hao.xu@linux.dev
State New
Headers show
Series io_uring getdents | expand

Commit Message

Hao Xu Aug. 25, 2023, 1:54 p.m. UTC 
From: Hao Xu <howeyxu@tencent.com>

if the log transaction is a sync one, let's fail the nowait try and
return -EAGAIN directly since sync transaction means blocked by IO.

Signed-off-by: Hao Xu <howeyxu@tencent.com>
---
 fs/xfs/xfs_trans.c | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

Comments

Dave Chinner Aug. 25, 2023, 9:58 p.m. UTC | #1 
On Fri, Aug 25, 2023 at 09:54:28PM +0800, Hao Xu wrote:
> From: Hao Xu <howeyxu@tencent.com>
> 
> if the log transaction is a sync one, let's fail the nowait try and
> return -EAGAIN directly since sync transaction means blocked by IO.
> 
> Signed-off-by: Hao Xu <howeyxu@tencent.com>
> ---
>  fs/xfs/xfs_trans.c | 14 +++++++++++++-
>  1 file changed, 13 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/xfs/xfs_trans.c b/fs/xfs/xfs_trans.c
> index 7988b4c7f36e..f1f84a3dd456 100644
> --- a/fs/xfs/xfs_trans.c
> +++ b/fs/xfs/xfs_trans.c
> @@ -968,12 +968,24 @@ __xfs_trans_commit(
>  	xfs_csn_t		commit_seq = 0;
>  	int			error = 0;
>  	int			sync = tp->t_flags & XFS_TRANS_SYNC;
> +	bool			nowait = tp->t_flags & XFS_TRANS_NOWAIT;
> +	bool			perm_log = tp->t_flags & XFS_TRANS_PERM_LOG_RES;
>  
>  	trace_xfs_trans_commit(tp, _RET_IP_);
>  
> +	if (nowait && sync) {
> +		/*
> +		 * Currently nowait is only from xfs_vn_update_time()
> +		 * so perm_log is always false here, but let's make
> +		 * code general.
> +		 */
> +		if (perm_log)
> +			xfs_defer_cancel(tp);
> +		goto out_unreserve;
> +	}

This is fundamentally broken.  We cannot about a transaction commit
with dirty items at this point with shutting down the filesystem.

This points to XFS_TRANS_NOWAIT being completely broken, too,
because we don't call xfs_trans_set_sync() until just before we
commit the transaction. At this point, it is -too late- for
nowait+sync to be handled gracefully, and it will *always* go bad.

IOWs, the whole transaction "nowait" semantics as designed and
implemented is not a workable solution....

-Dave.
diff mbox series

Patch

diff --git a/fs/xfs/xfs_trans.c b/fs/xfs/xfs_trans.c
index 7988b4c7f36e..f1f84a3dd456 100644
--- a/fs/xfs/xfs_trans.c
+++ b/fs/xfs/xfs_trans.c
@@ -968,12 +968,24 @@  __xfs_trans_commit(
 	xfs_csn_t		commit_seq = 0;
 	int			error = 0;
 	int			sync = tp->t_flags & XFS_TRANS_SYNC;
+	bool			nowait = tp->t_flags & XFS_TRANS_NOWAIT;
+	bool			perm_log = tp->t_flags & XFS_TRANS_PERM_LOG_RES;
 
 	trace_xfs_trans_commit(tp, _RET_IP_);
 
+	if (nowait && sync) {
+		/*
+		 * Currently nowait is only from xfs_vn_update_time()
+		 * so perm_log is always false here, but let's make
+		 * code general.
+		 */
+		if (perm_log)
+			xfs_defer_cancel(tp);
+		goto out_unreserve;
+	}
 	error = xfs_trans_run_precommits(tp);
 	if (error) {
-		if (tp->t_flags & XFS_TRANS_PERM_LOG_RES)
+		if (perm_log)
 			xfs_defer_cancel(tp);
 		goto out_unreserve;
 	}