On Wed, May 11, 2022 at 11:01:01AM -0700, Minchan Kim wrote:
On Sun, May 08, 2022 at 07:47:02PM -0700, Sultan Alsawaf wrote:
Cc: stable@vger.kernel.org Fixes: 48b4800a1c6a ("zsmalloc: page migration support")
Shouldn't the fix be Fixes: 77ff465799c6 ("zsmalloc: zs_page_migrate: skip unnecessary loops but not return -EBUSY if zspage is not inuse)? Because we didn't migrate ZS_EMPTY pages before.
Hi,
Yeah, 77ff465799c6 indeed seems like the commit that introduced the bug.
I couldn't get the point here. Why couldn't we simple lock zspage migration?
diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c index 9152fbde33b5..05ff2315b7b1 100644 --- a/mm/zsmalloc.c +++ b/mm/zsmalloc.c @@ -1987,7 +1987,10 @@ static void async_free_zspage(struct work_struct *work) list_for_each_entry_safe(zspage, tmp, &free_pages, list) { list_del(&zspage->list);
migrate_read_lock(zspage); lock_zspage(zspage);migrate_read_unlock(zspage);get_zspage_mapping(zspage, &class_idx, &fullness); VM_BUG_ON(fullness != ZS_EMPTY);
There are two problems with this: 1. migrate_read_lock() is a rwlock and lock_page() can sleep. 2. This will cause a deadlock because it violates the lock ordering in zs_page_migrate(), since zs_page_migrate() takes migrate_write_lock() under the page lock.
Sultan