On Sat, Dec 07, 2019 at 11:40:17AM +0800, Herbert Xu wrote:
>
> > Also, some comments (e.g. for struct crypto_spawn and crypto_remove_spawns())
> > would be really helpful to understand what's going on here.
>
> crypto_remove_spawns is performing a depth-first walk on cra_users
> without recursion. In the specific case of a spawn removal triggered
> by a new registration, we will halt the walk when we hit the
> newly registered algorithm, and undo any actions that we did
> on the path leading to that object. The function crypto_more_spawns
> performs the undo action.
>
> I'll add this to crypto_remove_spawns.
Here is the patch:
---8<---
This patch explains the logic behind crypto_remove_spawns and its
underling crypto_more_spawns.
Signed-off-by: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
diff --git a/crypto/algapi.c b/crypto/algapi.c
index adb516380be9..8ef771ab0ee3 100644
--- a/crypto/algapi.c
+++ b/crypto/algapi.c
@@ -82,6 +82,15 @@ static void crypto_destroy_instance(struct crypto_alg *alg)
crypto_tmpl_put(tmpl);
}
+/*
+ * This function adds a spawn to the list secondary_spawns which
+ * will be used at the end of crypto_remove_spawns to unregister
+ * instances, unless the spawn happens to be one that is depended
+ * on by the new algorithm (nalg in crypto_remove_spawns).
+ *
+ * This function is also responsible for resurrecting any algorithms
+ * in the dependency chain of nalg by unsetting n->dead.
+ */
static struct list_head *crypto_more_spawns(struct crypto_alg *alg,
struct list_head *stack,
struct list_head *top,
@@ -128,6 +137,12 @@ static void crypto_remove_instance(struct crypto_instance *inst,
BUG_ON(!list_empty(&inst->alg.cra_users));
}
+/*
+ * Given an algorithm alg, remove all algorithms that depend on it
+ * through spawns. If nalg is not null, then exempt any algorithms
+ * that is depended on by nalg. This is useful when nalg itself
+ * depends on alg.
+ */
void crypto_remove_spawns(struct crypto_alg *alg, struct list_head *list,
struct crypto_alg *nalg)
{
@@ -146,6 +161,11 @@ void crypto_remove_spawns(struct crypto_alg *alg, struct list_head *list,
list_move(&spawn->list, &top);
}
+ /*
+ * Perform a depth-first walk starting from alg through
+ * the cra_users tree. The list stack records the path
+ * from alg to the current spawn.
+ */
spawns = ⊤
do {
while (!list_empty(spawns)) {
@@ -180,6 +200,11 @@ void crypto_remove_spawns(struct crypto_alg *alg, struct list_head *list,
} while ((spawns = crypto_more_spawns(alg, &stack, &top,
&secondary_spawns)));
+ /*
+ * Remove all instances that are marked as dead. Also
+ * complete the resurrection of the others by moving them
+ * back to the cra_users list.
+ */
list_for_each_entry_safe(spawn, n, &secondary_spawns, list) {
if (!spawn->dead)
list_move(&spawn->list, &spawn->alg->cra_users);
--
Email: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
