### Reasoning Steps for Generating the Patch

#### Step 1: Root Cause Analysis

1. **Understanding the Code Context**:
   - The function `hpsa_get_pdisk_of_ioaccel2` is responsible for obtaining physical disk information.
   - It allocates memory for `physicals` using `kzalloc` and then calls `hpsa_scsi_do_report_phys_luns` with this allocated memory.

2. **Identifying the Vulnerability**:
   - The vulnerability is identified as CWE-476: NULL Pointer Dereference.
   - The line in question is:
     ```c
     if (hpsa_scsi_do_report_phys_luns(h, (ReportLUNdata *)physicals, reportsize, extended))
     ```
   - This line uses `physicals` without checking if the memory allocation was successful.

3. **Potential Vulnerable Behavior**:
   - If `kzalloc` fails, it returns `NULL`.
   - Dereferencing a `NULL` pointer in the function `hpsa_scsi_do_report_phys_luns` can lead to a crash or undefined behavior.

#### Step 2: Fixing Strategy

1. **Adding a NULL Check**:
   - To prevent the NULL pointer dereference, we need to check if `physicals` is `NULL` after the `kzalloc` call.
   - If `physicals` is `NULL`, the function should handle this gracefully, typically by returning an error code or a specific value indicating failure.

2. **Implementing the Patch**:
   - Insert a check right after the `kzalloc` call to verify if `physicals` is `NULL`.
   - If `physicals` is `NULL`, return an appropriate value (in this case, `0`).

### Conclusion

The patch ensures that the function does not proceed with a `NULL` pointer, thus preventing the NULL pointer dereference vulnerability. The steps to generate the patch are as follows:

1. **Original Code**:
   ```c
   physicals = kzalloc(reportsize, GFP_KERNEL);
   if (hpsa_scsi_do_report_phys_luns(h, (ReportLUNdata *)physicals, reportsize, extended))
   ```

2. **Patched Code**:
   ```c
   physicals = kzalloc(reportsize, GFP_KERNEL);
   if (physicals == NULL)
   {
       return 0;
   }
   if (hpsa_scsi_do_report_phys_luns(h, (ReportLUNdata *)physicals, reportsize, extended))
   ```

### Detailed Steps for the Patch

1. **Memory Allocation**:
   - Allocate memory for `physicals` using `kzalloc`.
   - `physicals = kzalloc(reportsize, GFP_KERNEL);`

2. **NULL Check**:
   - Immediately check if `physicals` is `NULL`.
   - `if (physicals == NULL)`

3. **Handle NULL Case**:
   - If `physicals` is `NULL`, return `0` to indicate failure.
   - ```c
     {
         return 0;
     }
     ```

4. **Proceed with Function Call**:
   - If `physicals` is not `NULL`, proceed with the function call.
   - `if (hpsa_scsi_do_report_phys_luns(h, (ReportLUNdata *)physicals, reportsize, extended))`

By following these steps, the patch ensures that the function handles memory allocation failures gracefully, preventing potential crashes or undefined behavior due to NULL pointer dereference.