[PATCH 2/2] liveupdate: Remember FLB retrieve() status

[David Matlack <dmatlack@google.com>]

LUO keeps track of successful retrieve attempts on an FLB. It does so
to avoid multiple retrievals of the same FLB. Multiple retrievals cause
problems because once the FLB is retrieved, the serialized data
structures are likely freed and the FLB is likely in a very different
state from what the code expects.

All this works well when retrieve succeeds. When it fails,
luo_flb_retrieve_one() returns the error immediately, without ever
storing anywhere that a retrieve was attempted or what its error code
was. If the user attempts to retrieve another file registered with the
same FLB, LUO will attempt to call the FLB's retrieve() callback again.

The retry is problematic for much of the same reasons listed above. The
FLB is likely in a very different state than what the retrieve logic
normally expects (e.g. some KHO pages may have already been restored and
freed).

There is no sane way of attempting the retrieve again. Remember the
error retrieve returned and directly return it on a retry.

This is done by changing the retrieved bool to a retrieve_status
integer. A value of 0 means retrieve was never attempted, a positive
value means it succeeded, and a negative value means it failed and the
error code is the value.

This is similar to commit f85b1c6af5bc ("liveupdate: luo_file: remember
retrieve() status") which did the same for LUO files.

Fixes: cab056f2aae7 ("liveupdate: luo_flb: introduce File-Lifecycle-Bound global state")
Assisted-by: Gemini:gemini-3-pro-preview
Signed-off-by: David Matlack <dmatlack@google.com>
---
 include/linux/liveupdate.h  |  6 ++++--
 kernel/liveupdate/luo_flb.c | 10 +++++++---
 2 files changed, 11 insertions(+), 5 deletions(-)

diff --git a/include/linux/liveupdate.h b/include/linux/liveupdate.h
index c344bf987b63..63ea5417de84 100644
--- a/include/linux/liveupdate.h
+++ b/include/linux/liveupdate.h
@@ -173,7 +173,9 @@ struct liveupdate_flb_ops {
  * @lock:      A mutex that protects all fields within this structure, providing
  *             the synchronization service for the FLB's ops.
  * @finished:  True once the FLB's finish() callback has run.
- * @retrieved: True once the FLB's retrieve() callback has run.
+ * @retrieve_status: Status code indicating whether retrieve() has been
+ *                   attempted. 0 means not attempted, 1 means successful,
+ *                   and negative value means it failed with that error code.
  */
 struct luo_flb_private_state {
 	refcount_t count;
@@ -181,7 +183,7 @@ struct luo_flb_private_state {
 	void *obj;
 	struct mutex lock;
 	bool finished;
-	bool retrieved;
+	int retrieve_status;
 };
 
 /*
diff --git a/kernel/liveupdate/luo_flb.c b/kernel/liveupdate/luo_flb.c
index 7ddef552ff6b..f8852f7e62e5 100644
--- a/kernel/liveupdate/luo_flb.c
+++ b/kernel/liveupdate/luo_flb.c
@@ -170,7 +170,10 @@ static int luo_flb_retrieve_one(struct liveupdate_flb *flb)
 	if (private->incoming.finished)
 		return -ENODATA;
 
-	if (private->incoming.retrieved)
+	if (private->incoming.retrieve_status < 0)
+		return private->incoming.retrieve_status;
+
+	if (private->incoming.retrieve_status > 0)
 		return 0;
 
 	if (!fh->active)
@@ -196,12 +199,13 @@ static int luo_flb_retrieve_one(struct liveupdate_flb *flb)
 
 	err = flb->ops->retrieve(&args);
 	if (err) {
+		private->incoming.retrieve_status = err;
 		module_put(flb->ops->owner);
 		return err;
 	}
 
 	private->incoming.obj = args.obj;
-	private->incoming.retrieved = true;
+	private->incoming.retrieve_status = 1;
 
 	return 0;
 }
@@ -215,7 +219,7 @@ void liveupdate_flb_put_incoming(struct liveupdate_flb *flb)
 		if (!refcount_dec_and_test(&private->incoming.count))
 			return;
 
-		if (!private->incoming.retrieved) {
+		if (private->incoming.retrieve_status <= 0) {
 			int err = luo_flb_retrieve_one(flb);
 
 			if (WARN_ON(err))
-- 
2.54.0.823.g6e5bcc1fc9-goog