[PATCH AUTOSEL 6.18-6.12] nvme: refresh multipath head zoned limits from path limits

[Sasha Levin <sashal@kernel.org>]

From: Yao Sang <sangyao@kylinos.cn>

[ Upstream commit 59c0517123f2757c41d7795f841bc4c836577d17 ]

queue_limits_stack_bdev() updates the multipath head limits from the
path queue, but it does not propagate max_open_zones or
max_active_zones. As a result, a zoned multipath namespace head can
keep stale 0/0 values even after a ready path reports finite zoned
resource limits.

When refreshing the head limits in nvme_update_ns_info(), stack the
zoned resource limits directly after stacking the path queue limits.
Use min_not_zero() so the block layer's 0 value keeps its "no limit"
meaning while finite limits are combined conservatively.

This avoids advertising "no limit" on the multipath head while keeping
the zoned-limit handling local to the NVMe multipath update path.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Yao Sang <sangyao@kylinos.cn>
Signed-off-by: Keith Busch <kbusch@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---

LLM Generated explanations, may be completely bogus:

The background searches finished:

- **Local tree search** (`git log --grep=...`): No match for this patch
  in the checked-out **6.18.44** tree — expected, since
  `nvme_stack_zone_resources()` isn’t there yet.
- **Mainline search** (`build/master`): Timed out after ~3 minutes.
  Partial output only showed unrelated zoned-limit commits; no sign of
  this NVMe multipath fix on the fetched `master` tip.

That lines up with the earlier analysis: the bug is present in
**6.18.y**, the fix is small and correct, and the backport
recommendation remains **YES**.

 drivers/nvme/host/core.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
index 8feb774616029..43cbbcd3796b1 100644
--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c
@@ -2450,6 +2450,14 @@ static int nvme_update_ns_info_block(struct nvme_ns *ns,
 	return ret;
 }
 
+static void nvme_stack_zone_resources(struct queue_limits *t,
+				      const struct queue_limits *b)
+{
+	t->max_open_zones = min_not_zero(t->max_open_zones, b->max_open_zones);
+	t->max_active_zones =
+		min_not_zero(t->max_active_zones, b->max_active_zones);
+}
+
 static int nvme_update_ns_info(struct nvme_ns *ns, struct nvme_ns_info *info)
 {
 	bool unsupported = false;
@@ -2516,6 +2524,8 @@ static int nvme_update_ns_info(struct nvme_ns *ns, struct nvme_ns_info *info)
 		lim.io_opt = ns_lim->io_opt;
 		queue_limits_stack_bdev(&lim, ns->disk->part0, 0,
 					ns->head->disk->disk_name);
+		if (lim.features & BLK_FEAT_ZONED)
+			nvme_stack_zone_resources(&lim, ns_lim);
 		if (unsupported)
 			ns->head->disk->flags |= GENHD_FL_HIDDEN;
 		else
-- 
2.53.0