Re: [PATCH] md: remove REQ_NOWAIT support

[yu kuai]

Hi,

在 2026/6/28 22:27, Abd-Alrhman Masalkhi 写道:
> REQ_NOWAIT support in md is fundamentally incomplete. While reads can
> avoid some blocking paths, write requests can still encounter cases
> where one mirror succeeds while another returns -EAGAIN. At that point
> md cannot distinguish queue pressure from a real device failure, so it
> can neither record a bad block nor safely retry the write without
> REQ_NOWAIT, leaving mirrors with divergent data.
>
> Rather than continue advertising REQ_NOWAIT support that cannot be
> implemented correctly, remove it from md and its raid personalities.
> This simplifies the waiting paths and avoids exposing incorrect
> non-blocking semantics.
>
> Fixes: bf2c411bb1cf ("md: raid456 add nowait support")
> Fixes: c9aa889b035f ("md: raid10 add nowait support")
> Fixes: 5aa705039c4f ("md: raid1 add nowait support")
> Fixes: f51d46d0e7cb ("md: add support for REQ_NOWAIT")
> Suggested-by: Yu Kuai<yukuai@xxxxxxx>
> Signed-off-by: Abd-Alrhman Masalkhi<abd.masalkhi@xxxxxxxxx>
> ---
>   drivers/md/md-bitmap.c   |  9 +---
>   drivers/md/md-bitmap.h   |  2 +-
>   drivers/md/md-llbitmap.c | 10 +----
>   drivers/md/md.c          | 15 ++-----
>   drivers/md/raid1-10.c    |  8 ++--
>   drivers/md/raid1.c       | 91 +++++++++-------------------------------
>   drivers/md/raid10.c      | 80 +++++++++--------------------------
>   drivers/md/raid5.c       | 13 ------
>   8 files changed, 51 insertions(+), 177 deletions(-)

Applied to md-7.3 with a few changes, please check:

md: remove REQ_NOWAIT support from raid1/10/456 - 
kernel/git/mdraid/linux.git - song's fork of linux.git <https://git.kernel.org/pub/scm/linux/kernel/git/mdraid/linux.git/commit/?h=md-7.3&id=3fe5b7c9fb72ccc29bfd0f955b124892af7e3674>

- rebase raid1/raid10 with latest code;
- keep nowait for raid0/linear;
- keep nowait for md_handle_request, as raid0/linear will need it;

-- 
Thanks,
Kuai