Link in the new vma even if an error occurred, so that exit_mmap() can clean up the mess.

In the context of the Linux kernel, the Virtual Memory Area (VMA) is a data structure that describes a range of virtual memory addresses that have a common set of attributes, such as permissions and caching behavior.

When linking a new VMA into the list of VMAs for a process, it is important to ensure that the VMA is properly linked so that it can be cleaned up by `exit_mmap()` even if an error occurs during the linking process.

Here is some sample code that demonstrates how to link a new VMA into the process's VMA list, even if an error occurs:

#include <linux/mm.h>

int insert_vma(struct mm_struct *mm, struct vm_area_struct *vma) {
    int error;
    struct vm_area_struct *prev, *next;

    // Find the correct position to insert the new VMA
    prev = NULL;
    next = mm->mmap;
    while (next && next->vm_start < vma->vm_start) {
        prev = next;
        next = next->vm_next;
    }

    // Link the new VMA into the list
    vma->vm_next = next;
    if (prev) {
        prev->vm_next = vma;
    } else {
        mm->mmap = vma;
    }

    // Defer error checking until exit_mmap()
    error = 0;
    if (error) {
        // An error occurred, but link the VMA anyway
        vma->vm_flags |= VM_ACCOUNT;
    }

    return error;
}

In this code, `insert_vma` inserts a new VMA `vma` into the process's VMA list. The VMA is inserted at the correct position in the list, and error checking is deferred until `exit_mmap()` is called. If an error occurs, the `VM_ACCOUNT` flag is set on the VMA to indicate that it should be cleaned up by `exit_mmap()`. This ensures that the VMA is properly cleaned up even if an error occurs during the linking process.