On 07/03, Colin Cross wrote:
>
> The names of named anonymous vmas are shown in /proc/pid/maps
> as [anon:<name>]. The name of all named vmas are shown in
> /proc/pid/smaps in a new "Name" field that is only present
> for named vmas.
And this is the only purpose, yes?
> static long madvise_behavior(struct vm_area_struct * vma,
> struct vm_area_struct **prev,
> - unsigned long start, unsigned long end, int behavior)
> + unsigned long start, unsigned long end, int behavior,
> + void *arg, size_t arg_len)
> {
> struct mm_struct * mm = vma->vm_mm;
> int error = 0;
> pgoff_t pgoff;
> unsigned long new_flags = vma->vm_flags;
> + struct vma_name *new_name = vma->vm_name;
>
> switch (behavior) {
> case MADV_NORMAL:
> @@ -93,16 +97,28 @@ static long madvise_behavior(struct vm_area_struct * vma,
> if (error)
> goto out;
> break;
> + case MADV_NAME:
> + if (arg) {
> + new_name = vma_name_get_from_str(arg, arg_len);
> + if (!new_name) {
> + error = -ENOMEM;
> + goto out;
> + }
> + } else {
> + new_name = NULL;
> + }
> + break;
> }
>
> - if (new_flags == vma->vm_flags) {
> + if (new_flags == vma->vm_flags && new_name == vma->vm_name) {
> *prev = vma;
> goto out;
> }
>
> pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
> *prev = vma_merge(mm, *prev, start, end, new_flags, vma->anon_vma,
> - vma->vm_file, pgoff, vma_policy(vma));
> + vma->vm_file, pgoff, vma_policy(vma),
> + new_name);
> if (*prev) {
> vma = *prev;
> goto success;
> @@ -127,8 +143,17 @@ success:
> * vm_flags is protected by the mmap_sem held in write mode.
> */
> vma->vm_flags = new_flags;
> + if (vma->vm_name != new_name) {
> + if (vma->vm_name)
> + vma_name_put(vma->vm_name);
> + if (new_name)
> + vma_name_get(new_name);
> + vma->vm_name = new_name;
> + }
So we change vma->vm_name after vma_merge(). But given that is_mergeable_vma()
checks vma->vm_name with this patch, this means that we can have 2 vma's with
the same ->vm_name which should be merged?
IOW. Suppose that we have vma with vm_start = START, end = START + 2 * PAGE_SIZE.
Suppose that an application does
MADV_NAME(START, PAGE_SIZE, "MY_NAME");
MADV_NAME(START + PAGE_SIZE, PAGE_SIZE, "MY_NAME");
The 1st MADV_NAME will split this vma, the 2nd won't merge. Not that I think
this is buggy, just a bit inconsistent imho.
And I guess vma_name_get(new_name) is not needed, you can simply nullify it
after changing ->vm_name to avoid vma_name_put() below.
Oleg.
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