Subject: Re: proto_unregister sleeps while atomic

From: Patrick McHardy <[email-masked]>
Date: Wed, 07 Sep 2005 01:02:01 +0200

Daniele Orlandi wrote:
> I'm looking at proto_unregister() in linux-2.6.13:
> 
> Il calls kmem_cache_destroy() while holding proto_list_lock:
> 
> void proto_unregister(struct proto *prot)
> {
>         write_lock(&proto_list_lock);
> 
>         if (prot->slab != NULL) {
>                 kmem_cache_destroy(prot->slab);
> 
> 
> However, kmem_cache_destroy() may sleep:
> 
>         /* Find the cache in the chain of caches. */
>         down(&cache_chain_sem);
>         ^^^^^^^^^^^^^^^^^^^^^^^
> 
> Am I seeing it right?

You're right, good catch. This patch fixes it by moving the lock
down to the list-operation which it is supposed to protect.
[NET]: proto_unregister: fix sleeping while atomic

proto_unregister holds a lock while calling kmem_cache_destroy, which can
sleep.

Noticed by Daniele Orlandi <[email-masked]>.

Signed-off-by: Patrick McHardy <[email-masked]>

---
commit 90fdf8bc78b52d40190766c5496a3d8c24903be8
tree 54048218d981ab263b37e0de09ad52f4bd49a000
parent 591bd554f58b7d363167760a606d2a84696772da
author Patrick McHardy <[email-masked]> Wed, 07 Sep 2005 01:00:00 +0200
committer Patrick McHardy <[email-masked]> Wed, 07 Sep 2005 01:00:00 +0200

 net/core/sock.c |    3 +--
 1 files changed, 1 insertions(+), 2 deletions(-)

diff --git a/net/core/sock.c b/net/core/sock.c
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -1528,8 +1528,6 @@ EXPORT_SYMBOL(proto_register);
 
 void proto_unregister(struct proto *prot)
 {
-	write_lock(&proto_list_lock);
-
 	if (prot->slab != NULL) {
 		kmem_cache_destroy(prot->slab);
 		prot->slab = NULL;
@@ -1551,6 +1549,7 @@ void proto_unregister(struct proto *prot
 		prot->twsk_slab = NULL;
 	}
 
+	write_lock(&proto_list_lock);
 	list_del(&prot->node);
 	write_unlock(&proto_list_lock);
 }