diff mbox series

[24/29] xfs: support nowait for xfs_buf_read_map()

Message ID 20230825135431.1317785-25-hao.xu@linux.dev (mailing list archive)
State New, archived
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>

This causes xfstests generic/232 hung in umount process, waiting for ail
push, so I comment it for now, need some hints from xfs folks.
Not a real patch.

Signed-off-by: Hao Xu <howeyxu@tencent.com>
---
 fs/xfs/xfs_buf.c | 7 +++++++
 1 file changed, 7 insertions(+)

Comments

Dave Chinner Aug. 25, 2023, 9:53 p.m. UTC | #1
On Fri, Aug 25, 2023 at 09:54:26PM +0800, Hao Xu wrote:
> From: Hao Xu <howeyxu@tencent.com>
> 
> This causes xfstests generic/232 hung in umount process, waiting for ail
> push, so I comment it for now, need some hints from xfs folks.
> Not a real patch.
> 
> Signed-off-by: Hao Xu <howeyxu@tencent.com>
> ---
>  fs/xfs/xfs_buf.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
> index cdad80e1ae25..284962a9f31a 100644
> --- a/fs/xfs/xfs_buf.c
> +++ b/fs/xfs/xfs_buf.c
> @@ -828,6 +828,13 @@ xfs_buf_read_map(
>  	trace_xfs_buf_read(bp, flags, _RET_IP_);
>  
>  	if (!(bp->b_flags & XBF_DONE)) {
> +//		/*
> +//		 * Let's bypass the _xfs_buf_read() for now
> +//		 */
> +//		if (flags & XBF_NOWAIT) {
> +//			xfs_buf_relse(bp);
> +//			return -EAGAIN;
> +//		}

This is *fundamentally broken*, and apart from anything else breaks
readahead.

IF we asked for a read, we cannot instantiate the buffer and then
*not issue any IO on it* and release it. That leaves an
uninitialised buffer in memory, and there's every chance that
something then trips over it and bad things happen.

A buffer like this *must* be errored out and marked stale so that
the next access to it will then re-initialise the buffer state and
trigger any preparatory work that needs to be done for the new
operation.

This comes back to my first comments that XBF_TRYLOCK cannot simpy
be replaced with XBF_NOWAIT semantics...

-Dave.
diff mbox series

Patch

diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
index cdad80e1ae25..284962a9f31a 100644
--- a/fs/xfs/xfs_buf.c
+++ b/fs/xfs/xfs_buf.c
@@ -828,6 +828,13 @@  xfs_buf_read_map(
 	trace_xfs_buf_read(bp, flags, _RET_IP_);
 
 	if (!(bp->b_flags & XBF_DONE)) {
+//		/*
+//		 * Let's bypass the _xfs_buf_read() for now
+//		 */
+//		if (flags & XBF_NOWAIT) {
+//			xfs_buf_relse(bp);
+//			return -EAGAIN;
+//		}
 		/* Initiate the buffer read and wait. */
 		XFS_STATS_INC(target->bt_mount, xb_get_read);
 		bp->b_ops = ops;