Re: [PATCH] migration: use parameters.mode in cpr_state_save

[Steven Sistare <steven.sistare@oracle.com>]

On 2/5/2025 4:52 PM, Steven Sistare wrote:
> On 2/5/2025 4:28 PM, Peter Xu wrote:
>> On Wed, Feb 05, 2025 at 12:54:01PM -0800, Steve Sistare wrote:
>>> qmp_migrate guarantees that cpr_channel is not null for
>>> MIG_MODE_CPR_TRANSFER when cpr_state_save is called:
>>>
>>>      qmp_migrate()
>>>          if (s->parameters.mode == MIG_MODE_CPR_TRANSFER && !cpr_channel) {
>>>              return;
>>>          }
>>>          cpr_state_save(cpr_channel)
>>>
>>> but cpr_state_save checks for mode differently before using channel,
>>> and Coverity cannot infer that they are equivalent in outgoing QEMU,
>>> and warns that channel may be NULL:
>>>
>>>      cpr_state_save(channel)
>>>          MigMode mode = migrate_mode();
>>>          if (mode == MIG_MODE_CPR_TRANSFER) {
>>>              f = cpr_transfer_output(channel, errp);
>>>
>>> To make Coverity happy, use parameters.mode in cpr_state_save.
>>>
>>> Resolves: Coverity CID 1590980
>>> Reported-by: Peter Maydell <peter.maydell@linaro.org>
>>> Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
>>> ---
>>>   migration/cpr.c | 3 ++-
>>>   1 file changed, 2 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/migration/cpr.c b/migration/cpr.c
>>> index 584b0b9..7f20bd5 100644
>>> --- a/migration/cpr.c
>>> +++ b/migration/cpr.c
>>> @@ -8,6 +8,7 @@
>>>   #include "qemu/osdep.h"
>>>   #include "qapi/error.h"
>>>   #include "migration/cpr.h"
>>> +#include "migration/migration.h"
>>>   #include "migration/misc.h"
>>>   #include "migration/options.h"
>>>   #include "migration/qemu-file.h"
>>> @@ -132,7 +133,7 @@ int cpr_state_save(MigrationChannel *channel, Error **errp)
>>>   {
>>>       int ret;
>>>       QEMUFile *f;
>>> -    MigMode mode = migrate_mode();
>>> +    MigMode mode = migrate_get_current()->parameters.mode;
>>
>> Are we sure this can make coverity happy?
> 
> It should, based on Peter Maydell's analysis, but I would appreciate
> if he could apply and test the fix.
> 
>> Another more straightforward change is caching migrate mode in
>> qmp_migrate() and also check that before invoking cpr_state_save().
> 
> Surely anyone would consider my one-line change to be straight forward.


Given that Coverity complains about channel, and not mode, this is the
most direct fix:

----------------------------------------
diff --git a/migration/cpr.c b/migration/cpr.c
index 59644e8..224b6ff 100644
--- a/migration/cpr.c
+++ b/migration/cpr.c
@@ -160,6 +160,7 @@ int cpr_state_save(MigrationChannel *channel, Error **errp)
      trace_cpr_state_save(MigMode_str(mode));

      if (mode == MIG_MODE_CPR_TRANSFER) {
+        g_assert(channel);
          f = cpr_transfer_output(channel, errp);
      } else {
          return 0;
-------------------------------

- Steve