On 06/13, Ingo Molnar wrote:
>
> @@ -169,29 +169,40 @@ void sync_global_pgds(unsigned long start, unsigned long end, int removed)
>
> for (address = start; address <= end; address += PGDIR_SIZE) {
> const pgd_t *pgd_ref = pgd_offset_k(address);
> - struct page *page;
> + struct task_struct *g, *p;
>
> /*
> - * When it is called after memory hot remove, pgd_none()
> - * returns true. In this case (removed == 1), we must clear
> - * the PGD entries in the local PGD level page.
> + * When this function is called after memory hot remove,
> + * pgd_none() already returns true, but only the reference
> + * kernel PGD has been cleared, not the process PGDs.
> + *
> + * So clear the affected entries in every process PGD as well:
> */
> if (pgd_none(*pgd_ref) && !removed)
> continue;
>
> - spin_lock(&pgd_lock);
> - list_for_each_entry(page, &pgd_list, lru) {
> + spin_lock(&pgd_lock); /* Implies rcu_read_lock() for the task list iteration: */
^^^^^^^^^^^^^^^^^^^^^^^
Hmm, but it doesn't if PREEMPT_RCU? No, no, I do not pretend I understand
how it actually works ;) But, say, rcu_check_callbacks() can be called from
irq and since spin_lock() doesn't increment current->rcu_read_lock_nesting
this can lead to rcu_preempt_qs()?
> + for_each_process_thread(g, p) {
> + struct mm_struct *mm;
> pgd_t *pgd;
> spinlock_t *pgt_lock;
>
> - pgd = (pgd_t *)page_address(page) + pgd_index(address);
> - /* the pgt_lock only for Xen */
> - pgt_lock = &pgd_page_get_mm(page)->page_table_lock;
> + task_lock(p);
> + mm = p->mm;
> + if (!mm) {
> + task_unlock(p);
> + continue;
> + }
Again, you can simplify this code and avoid for_each_process_thread() if
you use for_each_process() + find_lock_task_mm().
Oleg.
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