Subject: Re: proto_unregister sleeps while atomic

From: Patrick McHardy <[email-masked]>
Date: Wed, 07 Sep 2005 01:42:48 +0200

David S. Miller wrote:
> From: Patrick McHardy <[email-masked]>
> Date: Wed, 07 Sep 2005 01:02:01 +0200
> 
> 
>>You're right, good catch. This patch fixes it by moving the lock
>>down to the list-operation which it is supposed to protect.
> 
> 
> I think we need to unlink from the list first if you're
> going to do it this way.  Otherwise someone can find the
> protocol via lookup, and then bogusly try to use the SLAB
> cache we're freeing up.
> 
> Or does something else prevent this?

The only other user of proto_list besides proto_register, which
doesn't care, are the seqfs functions. They use the slab pointer,
but in a harmless way:

                    proto->slab == NULL ? "no" : "yes",

Anyway, I've moved it up to the top.
[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 d68b08edb26dfb58d18ab6c555d011572f9115a6
tree 1d14cf91ca5db6878b6af3953f85a34a6fe12a91
parent 591bd554f58b7d363167760a606d2a84696772da
author Patrick McHardy <[email-masked]> Wed, 07 Sep 2005 01:35:19 +0200
committer Patrick McHardy <[email-masked]> Wed, 07 Sep 2005 01:35:19 +0200

 net/core/sock.c |    5 ++---
 1 files changed, 2 insertions(+), 3 deletions(-)

diff --git a/net/core/sock.c b/net/core/sock.c
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -1529,6 +1529,8 @@ EXPORT_SYMBOL(proto_register);
 void proto_unregister(struct proto *prot)
 {
 	write_lock(&proto_list_lock);
+	list_del(&prot->node);
+	write_unlock(&proto_list_lock);
 
 	if (prot->slab != NULL) {
 		kmem_cache_destroy(prot->slab);
@@ -1550,9 +1552,6 @@ void proto_unregister(struct proto *prot
 		kfree(name);
 		prot->twsk_slab = NULL;
 	}
-
-	list_del(&prot->node);
-	write_unlock(&proto_list_lock);
 }
 
 EXPORT_SYMBOL(proto_unregister);