On 1/10/21 9:14 PM, Nathan Chancellor wrote:
> On Sun, Jan 10, 2021 at 01:57:26PM -0800, trix@xxxxxxxxxx wrote:
>> From: Tom Rix <trix@xxxxxxxxxx>
>>
>> clang static analysis reports this problem
>>
>> rnbd-clt.c:1212:11: warning: Branch condition evaluates to a
>> garbage value
>> else if (!first)
>> ^~~~~~
> Ah, is it complaining that the 'if (IS_ERR(sess)) {' section in
> find_or_create_sess() does not initialize first even though that will be
> caught by the 'if (sess == ERR_PTR(-ENOMEM))' in
> find_and_get_or_create_sess() because alloc_sess() only returns an
> -ENOMEM error pointer?
Reviewing the code, failure looks like it returns only -ENOMEM.
So the check is correct but brittle.
>
>> This is triggered in the find_and_get_or_create_sess() call
>> because the variable first is not initialized and the
>> earlier check is specifically for
>>
>> if (sess == ERR_PTR(-ENOMEM))
>>
>> This is false positive.
>>
>> But the if-check can be reduced by initializing first to
>> false and then returning if the call to find_or_creat_sess()
>> does not set it to true. When it remains false, either
>> sess will be valid or not. The not case is caught by
>> find_and_get_or_create_sess()'s caller rnbd_clt_map_device()
>>
>> sess = find_and_get_or_create_sess(...);
>> if (IS_ERR(sess))
>> return ERR_CAST(sess);
>>
>> Since find_and_get_or_create_sess() initializes first to false
>> setting it in find_or_create_sess() is not needed.
>>
>> Signed-off-by: Tom Rix <trix@xxxxxxxxxx>
> Every maintainer has their preference for where and how stuff gets
> initialized but this makes sense to me. I am not sure the commit above
> find_or_create_sess() is needed but again, personal preference.
Mostly this removes two unneeded branches at the cost of initializing a variable.
Secondary, the static analysis complaint is resolved.
Tom
>
> Reviewed-by: Nathan Chancellor <natechancellor@xxxxxxxxx>
>
>> ---
>> drivers/block/rnbd/rnbd-clt.c | 10 ++++------
>> 1 file changed, 4 insertions(+), 6 deletions(-)
>>
>> diff --git a/drivers/block/rnbd/rnbd-clt.c b/drivers/block/rnbd/rnbd-clt.c
>> index 96e3f9fe8241..251f747cf10d 100644
>> --- a/drivers/block/rnbd/rnbd-clt.c
>> +++ b/drivers/block/rnbd/rnbd-clt.c
>> @@ -919,6 +919,7 @@ static struct rnbd_clt_session *__find_and_get_sess(const char *sessname)
>> return NULL;
>> }
>>
>> +/* caller is responsible for initializing 'first' to false */
>> static struct
>> rnbd_clt_session *find_or_create_sess(const char *sessname, bool *first)
>> {
>> @@ -934,8 +935,7 @@ rnbd_clt_session *find_or_create_sess(const char *sessname, bool *first)
>> }
>> list_add(&sess->list, &sess_list);
>> *first = true;
>> - } else
>> - *first = false;
>> + }
>> mutex_unlock(&sess_lock);
>>
>> return sess;
>> @@ -1203,13 +1203,11 @@ find_and_get_or_create_sess(const char *sessname,
>> struct rnbd_clt_session *sess;
>> struct rtrs_attrs attrs;
>> int err;
>> - bool first;
>> + bool first = false;
>> struct rtrs_clt_ops rtrs_ops;
>>
>> sess = find_or_create_sess(sessname, &first);
>> - if (sess == ERR_PTR(-ENOMEM))
>> - return ERR_PTR(-ENOMEM);
>> - else if (!first)
>> + if (!first)
>> return sess;
>>
>> if (!path_cnt) {
>> --
>> 2.27.0
>>
