Re: [PATCH v2] nvme: remove stale namespaces by NSID range during scan

[Mohamed Khalfella <mkhalfella@purestorage.com>]

On Mon 2026-08-24 17:21:26 -0700, Randy Jennings wrote:
> On Sat, Aug 22, 2026 at 5:47 PM Mohamed Khalfella
> <mkhalfella@purestorage.com> wrote:
> >
> > nvme_scan_ns_list() drops the stale namespaces in each gap in the
> > reported NSID list one NSID at a time. Every iteration calls
> > nvme_find_get_ns() to look the namespace up and removes it if it is
> > present. The loop runs once per NSID in the gap rather than once per
> > namespace actually present.
> >
> > NSIDs are 32-bit, so a target with a sparse NSID space can make a
> > single gap spin the loop billions of times with nothing to remove.
> >
> >   watchdog: BUG: soft lockup - CPU#4 stuck for 26s!
> >   Workqueue: nvme-wq nvme_scan_work [nvme_core]
> >   RIP: 0010:__srcu_read_unlock+0xb/0x20
> >   Call Trace:
> >    nvme_find_get_ns+0x7d/0xb0 [nvme_core]
> >    nvme_scan_ns_list+0xe8/0x280 [nvme_core]
> >    nvme_scan_work+0x18a/0x280 [nvme_core]
> >    process_one_work+0x197/0x380
> >    worker_thread+0x2fe/0x410
> >    kthread+0xe0/0x100
> >
> > Rename nvme_remove_invalid_namespaces() to nvme_remove_nsid_range()
> > and give it an open (start, end) NSID range. ctrl->namespaces is
> > sorted by NSID, so the whole gap is dropped in a single walk that
> > stops once end is reached. This bounds the work by the namespaces
> > that are present instead of by the size of the gap.
> >
> > Fixes: 540c801c65eb ("NVMe: Implement namespace list scanning")
> > Signed-off-by: Mohamed Khalfella <mkhalfella@purestorage.com>
> > Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
> Reviewed-by: Randy Jennings <randyj@purestorage.com>
> 
> > ---
> >  drivers/nvme/host/core.c | 18 +++++++++---------
> 
> > -static void nvme_remove_invalid_namespaces(struct nvme_ctrl *ctrl,
> > -                                       unsigned nsid)
> > +static void nvme_remove_nsid_range(struct nvme_ctrl *ctrl, u32 start, u32 end)
> It is not intuitive to me that start is non-inclusive.  May we add
> a comment to that effect?

Yes, it is not intuitive. [start, end) makes more sense IMO. That is
said, this is how nvme_remove_invalid_namespaces() worked and I decided
not to change that because it is not part of the fix. I do not think a
comment will make a big difference here. The next person who works on
this code will read the nvme_remove_nsid_range(), it is a short
function, and figure out how it works.

> 
> >  {
> >         struct nvme_ns *ns, *next;
> >         LIST_HEAD(rm_list);
> >
> >         mutex_lock(&ctrl->namespaces_lock);
> >         list_for_each_entry_safe(ns, next, &ctrl->namespaces, list) {
> > -               if (ns->head->ns_id > nsid) {
> > +               if (ns->head->ns_id >= end)
> > +                       break;
> > +               if (ns->head->ns_id > start) {
> >                         list_del_rcu(&ns->list);