Re: [PATCH v5 3/5] liveupdate: block session mutations during reboot

[Pratyush Yadav]

On Mon, May 18 2026, Pasha Tatashin wrote:

> During the reboot() syscall, user processes may still be running
> concurrently and attempting to mutate sessions (e.g., creating,
> retrieving, or releasing sessions). To prevent this, introduce
> luo_session_serialize_rwsem to synchronize mutations with the
> serialization process.
>
> All session mutation operations (create, retrieve, release, ioctl) take
> the read lock. The serialization process (luo_session_serialize) takes
> the write lock and holds it indefinitely on success. This effectively
> freezes the LUO session subsystem during the transition to the new
> kernel. If serialization fails, the lock is released to allow recovery.

Good idea I think.

But, do we need a new mutex? Can't we use luo_session_header->rwsem?
Session creation and release take the header rwsem at one point anyway,
so perhaps we can just reuse that?

Also, do we need to block incoming sessions? They won't participate in
serialization, so perhaps we can leave those alone, and all the outgoing
sessions get protected by the outgoing session header rwsem?

>
> Fixes: 0153094d03df ("liveupdate: luo_session: add sessions support")
> Reported-by: Oskar Gerlicz Kowalczuk <oskar@gerlicz.space>
> Acked-by: Mike Rapoport (Microsoft) <rppt@xxxxxxxxxx>
> Signed-off-by: Pasha Tatashin <pasha.tatashin@xxxxxxxxxx>

-- 
Regards,
Pratyush Yadav