The memory hotplug code uses sync_global_pgds() to synchronize updates
to the global (&init_mm) kernel PGD and the task PGDs. It does this
by iterating over the pgd_list - which list closely tracks task
creation/destruction via fork/clone.
But we want to remove this list, so that it does not have to be
maintained from fork()/exit(), so convert the memory hotplug code
to use the task list to iterate over all pgds in the system.
Also improve the comments a bit, to make this function easier
to understand.
Only lightly tested, as I don't have a memory hotplug setup.
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Brian Gerst <brgerst@xxxxxxxxx>
Cc: Denys Vlasenko <dvlasenk@xxxxxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Waiman Long <Waiman.Long@xxxxxx>
Cc: linux-mm@xxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
arch/x86/mm/init_64.c | 38 +++++++++++++++++++++++++-------------
1 file changed, 25 insertions(+), 13 deletions(-)
diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
index 3fba623e3ba5..527d5d4d020c 100644
--- a/arch/x86/mm/init_64.c
+++ b/arch/x86/mm/init_64.c
@@ -160,8 +160,8 @@ static int __init nonx32_setup(char *str)
__setup("noexec32=", nonx32_setup);
/*
- * When memory was added/removed make sure all the processes MM have
- * suitable PGD entries in the local PGD level page.
+ * When memory was added/removed make sure all the process MMs have
+ * matching PGD entries in the local PGD level page as well.
*/
void sync_global_pgds(unsigned long start, unsigned long end, int removed)
{
@@ -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: */
+
+ 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;
+ }
+
+ pgd = mm->pgd;
+
+ /* The pgt_lock is only used by Xen: */
+ pgt_lock = &mm->page_table_lock;
spin_lock(pgt_lock);
if (!pgd_none(*pgd_ref) && !pgd_none(*pgd))
- BUG_ON(pgd_page_vaddr(*pgd)
- != pgd_page_vaddr(*pgd_ref));
+ BUG_ON(pgd_page_vaddr(*pgd) != pgd_page_vaddr(*pgd_ref));
if (removed) {
if (pgd_none(*pgd_ref) && !pgd_none(*pgd))
@@ -202,6 +213,7 @@ void sync_global_pgds(unsigned long start, unsigned long end, int removed)
}
spin_unlock(pgt_lock);
+ task_unlock(p);
}
spin_unlock(&pgd_lock);
}
--
2.1.4
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