Re: [PATCH] IPC: fix error case when idr-cache is empty in ipcget()

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Pierre Peiffer wrote:
With the use of idr to store the ipc, the case where the idr cache is
empty, when idr_get_new is called (this may happen even if we call
idr_pre_get() before), is not well handled: it lets semget()/shmget()/msgget()
return ENOSPC when this cache is empty, what 1. does not reflect the facts
and 2. does not conform to the man(s).

This patch fixes this by retrying the whole process of allocation in this case.

Note: we could directly return ENOMEM if idr_pre_get() fails, but it does not
mean that the cache is empty...


Pierre,

I agree with everythying, but not on idr_pre_get() failure: I think we should give up in that case: the tests on idr_pre_get() return code should remain IMHO (see after).


<snip>

@@ -309,17 +309,20 @@ int ipc_addid(struct ipc_ids* ids, struc
 int ipcget_new(struct ipc_namespace *ns, struct ipc_ids *ids,
 		struct ipc_ops *ops, struct ipc_params *params)
 {
-	int err;
-
-	err = idr_pre_get(&ids->ipcs_idr, GFP_KERNEL);
-
-	if (!err)
-		return -ENOMEM;
+	int err, alloc;
+retry:
+	alloc = idr_pre_get(&ids->ipcs_idr, GFP_KERNEL);
mutex_lock(&ids->mutex);
 	err = ops->getnew(ns, params);
 	mutex_unlock(&ids->mutex);
+ if (err == -EAGAIN) {
+		if (alloc)
+			goto retry;
+		else
+			err = -ENOMEM;
+	}
 	return err;
 }


ops->getnew will call idr_get_new() that should not be called if idr_pre_get() has failed. So I think that we should give up if idr_pre_get() fails and the test on idr_pre_get() return code should not be removed.

@@ -372,9 +375,9 @@ int ipcget_public(struct ipc_namespace *
 {
 	struct kern_ipc_perm *ipcp;
 	int flg = params->flg;
-	int err;
-
-	err = idr_pre_get(&ids->ipcs_idr, GFP_KERNEL);
+	int err, alloc;
+retry:
+	alloc = idr_pre_get(&ids->ipcs_idr, GFP_KERNEL);
mutex_lock(&ids->mutex);
 	ipcp = ipc_findkey(ids, params->key);
@@ -382,8 +385,6 @@ int ipcget_public(struct ipc_namespace *
 		/* key not used */
 		if (!(flg & IPC_CREAT))
 			err = -ENOENT;
-		else if (!err)
-			err = -ENOMEM;
 		else
 			err = ops->getnew(ns, params);

Same remark as above:
ops->getnew will call idr_get_new() that should not be called if idr_pre_get() has failed. So I think that we should give up if idr_pre_get() fails and this this test should not be removed.


Regards,
Nadia




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