Logically dead code at fs/afs/cell.c:206

Logically dead code at fs/afs/cell.c:206

[Gustavo A. R. Silva]

Hi David,

Today Coverity reported a "Logically dead code" issue at fs/afs/cell.c:206:

        if (!excl) {
                rcu_read_lock();
                cell = afs_lookup_cell_rcu(net, name, namesz);
                rcu_read_unlock();
                if (!IS_ERR(cell)) {
                        if (excl) {
                                afs_put_cell(net, cell);
                                return ERR_PTR(-EEXIST);
                        }
                        goto wait_for_cell;
                }
        }

The problem is that when this code block is executed, the code block starting at line 211 makes no sense, as _excl_ can never be true.

I was wondering if the original intention was to null check _cell_ instead of checking _excl_. So I took a look into function afs_lookup_cell_rcu to see if _cell_ can be returned as a null pointer and at the same time the if condition at line 210 be true, but I couldn't see how that could be possible. It seems to me that when _ret_ is equal to zero, _cell_ cannot be null in afs_lookup_cell_rcu. But is case I'm wrong here and _cell_ could be null at line 210, then I think line 211 should be changed as follows:

diff --git a/fs/afs/cell.c b/fs/afs/cell.c
index 1858c91..a69a11f 100644
--- a/fs/afs/cell.c
+++ b/fs/afs/cell.c
@@ -208,7 +208,7 @@ struct afs_cell *afs_lookup_cell(struct afs_net *net,
                cell = afs_lookup_cell_rcu(net, name, namesz);
                rcu_read_unlock();
                if (!IS_ERR(cell)) {
-                       if (excl) {
+                       if (cell) {
                                afs_put_cell(net, cell);
                                return ERR_PTR(-EEXIST);
                        }

But I'm suspicious about it.

What do you think?

Thanks
--
Gustavo A. R. Silva

Re: Logically dead code at fs/afs/cell.c:206

[David Howells]

Gustavo A. R. Silva <garsilva@embeddedor.com> wrote:

> Today Coverity reported a "Logically dead code" issue at fs/afs/cell.c:206:
> 
>         if (!excl) {
>                 rcu_read_lock();
>                 cell = afs_lookup_cell_rcu(net, name, namesz);
>                 rcu_read_unlock();
>                 if (!IS_ERR(cell)) {
>                         if (excl) {
>                                 afs_put_cell(net, cell);
>                                 return ERR_PTR(-EEXIST);
>                         }
>                         goto wait_for_cell;
>                 }
>         }
> 
> The problem is that when this code block is executed, the code block
> starting at line 211 makes no sense, as _excl_ can never be true.

Good catch.  The interior "if (excl) { ... }" statement and body needs
removing entirely.  Originally the outer "if (!excl)" wrapping it wasn't
there.

David

Re: Logically dead code at fs/afs/cell.c:206

[Gustavo A. R. Silva]

Quoting David Howells <dhowells@redhat.com>:

> Gustavo A. R. Silva <garsilva@embeddedor.com> wrote:
>
>> Today Coverity reported a "Logically dead code" issue at fs/afs/cell.c:206:
>>
>>         if (!excl) {
>>                 rcu_read_lock();
>>                 cell = afs_lookup_cell_rcu(net, name, namesz);
>>                 rcu_read_unlock();
>>                 if (!IS_ERR(cell)) {
>>                         if (excl) {
>>                                 afs_put_cell(net, cell);
>>                                 return ERR_PTR(-EEXIST);
>>                         }
>>                         goto wait_for_cell;
>>                 }
>>         }
>>
>> The problem is that when this code block is executed, the code block
>> starting at line 211 makes no sense, as _excl_ can never be true.
>
> Good catch.  The interior "if (excl) { ... }" statement and body needs
> removing entirely.  Originally the outer "if (!excl)" wrapping it wasn't
> there.
>

I'll send a patch to remove that code.

Thanks for clarifying.
--
Gustavo A. R. Silva