[PATCH V4 3/9] nvme: fix race condition between connected uevent and STARTED_ONCE flag

[Maurizio Lombardi]

When a controller connects, nvme_start_ctrl() emits the
"NVME_EVENT=connected" uevent and sets the NVME_CTRL_STARTED_ONCE flag.
Currently, the uevent is emitted before the flag is set.

This creates a race condition for userspace tools (like udev rules)
that might rely on the "connected" event to configure sysfs attributes.
Specifically, if a udev rule attempts to set the newly introduced
`admin_timeout` attribute immediately after receiving the uevent,
the sysfs store function might evaluate the NVME_CTRL_STARTED_ONCE
bit before it is actually set, resulting in spurious -EBUSY error.

Swap the order of operations in nvme_start_ctrl() so that the
NVME_CTRL_STARTED_ONCE flag is set before the uevent is sent.
This guarantees that the admin_timeout can already be changed
when userspace is notified.

Signed-off-by: Maurizio Lombardi <mlombard at redhat.com>
---
 drivers/nvme/host/core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
index b1bfcd0a0e5b..22be8cf5e982 100644
--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c
@@ -5039,8 +5039,8 @@ void nvme_start_ctrl(struct nvme_ctrl *ctrl)
 		nvme_mpath_update(ctrl);
 	}
 
-	nvme_change_uevent(ctrl, "NVME_EVENT=connected");
 	set_bit(NVME_CTRL_STARTED_ONCE, &ctrl->flags);
+	nvme_change_uevent(ctrl, "NVME_EVENT=connected");
 }
 EXPORT_SYMBOL_GPL(nvme_start_ctrl);
 
-- 
2.54.0