Re: [PATCH v3 2/2] liveupdate: initialize incoming FLB state before finish

[Andrew Morton]

On Fri, 03 Apr 2026 09:04:25 +0000 Pratyush Yadav <pratyush@xxxxxxxxxx> wrote:

> On Thu, Apr 02 2026, Andrew Morton wrote:
> 
> > On Thu, 02 Apr 2026 13:28:33 +0000 Pratyush Yadav <pratyush@xxxxxxxxxx> wrote:
> >
> >> The state of an incoming FLB object is initialized when it is first
> >> used. The initialization is done via luo_flb_retrieve_one(), which looks
> >> at all the incoming FLBs, matches the FLB to its serialized entry, and
> >> initializes the incoming data and count.
> >> 
> >> luo_flb_file_finish_one() is called when finish is called for a file
> >> registered with this FLB. If no file handler has used the FLB by this
> >> point, the count stays un-initialized at 0. luo_flb_file_finish_one()
> >> then decrements this un-initialized count, leading to an underflow. This
> >> results in the FLB finish never being called since the count has
> >> underflowed to a very large value.
> >> 
> >> Fix this by making sure the FLB is retrieved before using its count.
> >
> > I like that the above tells people what the actual bug is!
> >
> > I still have both Leo's patches in mm.git, in wait-and-see mode.  What
> > to do here?  Should I upstream [1/2] and drop [2/2]?  Drop both and
> > revisit after -rc1?
> 
> These are independent fixes, so I would suggest keeping 1/2 regardless
> of what we do with 2/2. For 2/2, I would suggest replacing it with the
> version I sent in <2vxzmrzlfq4e.fsf@xxxxxxxxxx>.

OK, thanks.  I removed [2/2] "liveupdate: initialize incoming FLB state
before finish" from mm.git.

I added cc:stable to [1/1] "liveupdate: propagate file deserialization
failures" and altered its changelog to present it as a singleton patch
(no "Patch series..." header, no "This patch (of 2)", etc.  Below.

> Mike/Pasha/Leo, if you could review my version then that would be great.
> 
> Also Leo, please help with testing. I don't have a setup ready for
> testing this corner case. I can set something up mid next week, but it
> would be great if you can test this before that.
> 
> >
> > Also, did we consider cc:stable for these two?  Perhaps add the
> > cc:stable if we decide to attend to this after -rc1?
> 
> FLB landed in v7.0-rc1 so no need for cc:stable for patch 2/2. For patch
> 1/2, I think cc:stable does make sense, but it only landed in v6.19 so
> not super important given it is not LTS.

OK.  When considering cc:stable I personally don't pay attention to LTS
release cadence - I believe others do so.

Because it could be that some downstream people are using non-LTS Linus
kernels.  But then they should be looking at the Fixes: tags.



From: Leo Timmins <leotimmins1974@xxxxxxxxx>
Subject: liveupdate: propagate file deserialization failures
Date: Wed, 25 Mar 2026 12:46:07 +0800

luo_session_deserialize() ignored the return value from
luo_file_deserialize().  As a result, a session could be left partially
restored even though the /dev/liveupdate open path treats deserialization
failures as fatal.

Propagate the error so a failed file deserialization aborts session
deserialization instead of silently continuing.

Link: https://lkml.kernel.org/r/20260325044608.8407-1-leotimmins1974@xxxxxxxxx
Link: https://lkml.kernel.org/r/20260325044608.8407-2-leotimmins1974@xxxxxxxxx
Fixes: 16cec0d26521 ("liveupdate: luo_session: add ioctls for file preservation")
Signed-off-by: Leo Timmins <leotimmins1974@xxxxxxxxx>
Reviewed-by: Pasha Tatashin <pasha.tatashin@xxxxxxxxxx>
Reviewed-by: Pratyush Yadav <pratyush@xxxxxxxxxx>
Cc: Mike Rapoport <rppt@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---

 kernel/liveupdate/luo_session.c |    9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

--- a/kernel/liveupdate/luo_session.c~liveupdate-propagate-file-deserialization-failures
+++ a/kernel/liveupdate/luo_session.c
@@ -558,8 +558,13 @@ int luo_session_deserialize(void)
 		}
 
 		scoped_guard(mutex, &session->mutex) {
-			luo_file_deserialize(&session->file_set,
-					     &sh->ser[i].file_set_ser);
+			err = luo_file_deserialize(&session->file_set,
+						   &sh->ser[i].file_set_ser);
+		}
+		if (err) {
+			pr_warn("Failed to deserialize files for session [%s] %pe\n",
+				session->name, ERR_PTR(err));
+			return err;
 		}
 	}
 
_