[DPDK/ethdev Bug 1876] enic: pthread mutex in shared memory missing PTHREAD_PROCESS_SHARED (

[bugzilla@dpdk.org]

http://bugs.dpdk.org/show_bug.cgi?id=1876

            Bug ID: 1876
           Summary: enic: pthread mutex in shared memory missing
                    PTHREAD_PROCESS_SHARED (
           Product: DPDK
           Version: 25.11
          Hardware: All
                OS: All
            Status: UNCONFIRMED
          Severity: normal
          Priority: Normal
         Component: ethdev
          Assignee: dev@dpdk.org
          Reporter: stephen@networkplumber.org
  Target Milestone: ---

This the enic driver portion of existing bug 662

The enic driver has a pthread mutex in shared memory that is initialized
without `PTHREAD_PROCESS_SHARED`, which causes undefined behavior when used
across multiple processes.

### Affected Mutex

1. **`enic->admin_chan_lock`** (`drivers/net/enic/enic_sriov.c`, line 352)
   - Location: `struct enic` (device private data)
   - Purpose: Protects SR-IOV admin channel operations between VF and PF

### Why This Is a Problem

The `struct enic` is the device private data accessed via
`eth_dev->data->dev_private`, which resides in shared memory accessible by both
primary and secondary processes.

The mutex is initialized in `enic_enable_vf_admin_chan()`:
```c
pthread_mutex_init(&enic->admin_chan_lock, NULL);
```

And used to protect admin channel operations:
```c
static void lock_admin_chan(struct enic *enic)
{
    pthread_mutex_lock(&enic->admin_chan_lock);
}

static void unlock_admin_chan(struct enic *enic)
{
    pthread_mutex_unlock(&enic->admin_chan_lock);
}
```

Per POSIX, mutexes in shared memory accessed by multiple processes must be
initialized with `PTHREAD_PROCESS_SHARED` attribute. Without this,
synchronization between processes is undefined behavior.

### Suggested Fix

Initialize the mutex with `PTHREAD_PROCESS_SHARED`:

```c
static void
enic_init_shared_mutex(pthread_mutex_t *mutex)
{
    pthread_mutexattr_t attr;

    pthread_mutexattr_init(&attr);
    pthread_mutexattr_setpshared(&attr, PTHREAD_PROCESS_SHARED);
    pthread_mutex_init(mutex, &attr);
    pthread_mutexattr_destroy(&attr);
}
```

Then replace:
```c
pthread_mutex_init(&enic->admin_chan_lock, NULL);
```

With:
```c
enic_init_shared_mutex(&enic->admin_chan_lock);
```

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