Re: [PATCH v5 2/2] nvme-multipath: add fail_on_ctrl_loss sysfs attribute

[Nilay Shroff <nilay@linux.ibm.com>]

On 10/8/26 7:44 PM, Krishna Iyer wrote:
> When no usable path exists, I/O on a multipath namespace is queued
> until a path returns. With ctrl_loss_tmo=-1 that can be forever:
> during a long fabric outage any process waiting on the I/O is stuck in
> D state. We hit this on virtualization hosts, where a SIGKILLed VM
> process cannot exit while draining I/O to an unreachable NVMe/TCP
> target.
> 
> Nothing can fail this I/O without tearing something down: controller
> deletion takes every namespace on the controller with it.
> 
> Add a fail_on_ctrl_loss attribute on the ns-head disk: a persistent
> per-namespace policy to fail parked and newly arriving I/O instead of
> queueing it when no usable path exists. It is the namespace-scoped
> counterpart to the controller-scoped fast_io_fail_tmo: the trigger is
> an event userspace observes (a consumer known to be gone, for us a
> SIGKILLed VM the host must reap), not a duration picked up front, and
> sibling namespaces behind the same controllers keep queueing and ride
> out the outage.
> 
> A CONNECTING controller stops counting as an available path, and with
> no controllers left the policy overrides the delayed_removal_secs
> queue-if-no-path window; the two are opposites, so fail_on_ctrl_loss
> takes precedence when both are set. ANA change and controller resetting
> still queue, since both are transient. Controller state is untouched and
> reconnects continue. Like dm-multipath, the policy is transport
> agnostic.
> 
> Assisted-by: Claude:claude-fable-5
> Signed-off-by: Krishna Iyer<kiyer@crusoe.ai>

Looks good to me:

Reviewed-by: Nilay Shroff <nilay@linux.ibm.com>