[PATCH v2 06/10] mm/shmem_luo: Don't make early retrieve failures permanent

[David Matlack <dmatlack@google.com>]

If shmem_luo_retrieve() fails before it starts restoring the folios,
mark the failure as retryable and return the error without freeing the
serialized state. Nothing has consumed the preserved state at that
point, so the retrieve can be tried again. If no retrieve succeeds,
finish() frees the preserved folios, like it does for a file that was
never retrieved.

This fixes leaking the preserved folios when one of these early steps
fails, e.g. because the file has seals that this kernel doesn't support.
The retrieve freed the serialized state but not the folios, and finish()
then skipped the file because its retrieve had failed.

Assisted-by: LLM
Signed-off-by: David Matlack <dmatlack@google.com>
---
 mm/shmem_luo.c | 33 ++++++++++++++++++++-------------
 1 file changed, 20 insertions(+), 13 deletions(-)

diff --git a/mm/shmem_luo.c b/mm/shmem_luo.c
index b8d86055912d..bcac1bbb3db3 100644
--- a/mm/shmem_luo.c
+++ b/mm/shmem_luo.c
@@ -390,9 +390,9 @@ static void shmem_luo_finish(struct liveupdate_file_op_args *args)
 	struct shmem_luo_ser *ser;
 
 	/*
-	 * If retrieve was successful, nothing to do. If it failed, retrieve()
-	 * already cleaned up everything it could. So nothing to do there
-	 * either. Only need to clean up when retrieve was not called.
+	 * If retrieve was successful, nothing to do. If it failed permanently,
+	 * retrieve() already cleaned up everything it could. So nothing to do
+	 * there either. Only need to clean up when the file was not retrieved.
 	 */
 	if (args->retrieve_status)
 		return;
@@ -526,11 +526,16 @@ static int shmem_luo_retrieve(struct liveupdate_file_op_args *args)
 	if (!ser)
 		return -EINVAL;
 
+	/*
+	 * Nothing has consumed the preserved state until the folios are
+	 * restored below, so failures before that can be retried. If no
+	 * retrieve succeeds, finish() frees the preserved state.
+	 */
+	args->retryable = true;
+
 	/* Make sure the file only has seals supported by this version. */
-	if (ser->seals & ~SHMEM_LUO_ALL_SEALS) {
-		err = -EOPNOTSUPP;
-		goto free_ser;
-	}
+	if (ser->seals & ~SHMEM_LUO_ALL_SEALS)
+		return -EOPNOTSUPP;
 
 	/*
 	 * The seals are preserved. Allow sealing here so they can be added
@@ -539,8 +544,7 @@ static int shmem_luo_retrieve(struct liveupdate_file_op_args *args)
 	file = memfd_alloc_file("", MFD_ALLOW_SEALING);
 	if (IS_ERR(file)) {
 		pr_err("failed to setup file: %pe\n", file);
-		err = PTR_ERR(file);
-		goto free_ser;
+		return PTR_ERR(file);
 	}
 
 	err = memfd_add_seals(file, ser->seals);
@@ -552,17 +556,20 @@ static int shmem_luo_retrieve(struct liveupdate_file_op_args *args)
 	vfs_setpos(file, ser->pos, MAX_LFS_FILESIZE);
 	i_size_write(file_inode(file), ser->size);
 
+	/* The preserved state is consumed from here on. */
+	args->retryable = false;
+
 	if (ser->nr_folios) {
 		folios_ser = kho_restore_vmalloc(&ser->folios);
 		if (!folios_ser) {
 			err = -EINVAL;
-			goto put_file;
+			goto free_ser;
 		}
 
 		err = shmem_luo_retrieve_folios(file, folios_ser, ser->nr_folios);
 		vfree(folios_ser);
 		if (err)
-			goto put_file;
+			goto free_ser;
 	}
 
 	args->file = file;
@@ -570,10 +577,10 @@ static int shmem_luo_retrieve(struct liveupdate_file_op_args *args)
 
 	return 0;
 
-put_file:
-	fput(file);
 free_ser:
 	kho_restore_free(ser);
+put_file:
+	fput(file);
 	return err;
 }
 
-- 
2.56.0.257.gf7497c7d27-goog