Messages in this thread Patch in this message | | | Date | Thu, 19 Jun 2008 18:13:59 +0900 | From | KOSAKI Motohiro <> | Subject | [-mm][PATCH 2/5] migration_entry_wait fix. |
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From: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
In speculative page cache lookup protocol, page_count(page) is set to 0 while radix-tree modification is going on, truncation, migration, etc...
While page migration, a page fault to page under migration should wait unlock_page() and migration_entry_wait() waits for the page from its pte entry. It does get_page() -> wait_on_page_locked() -> put_page() now.
In page migration, page_freeze_refs() -> page_unfreeze_refs() is called.
Here, page_unfreeze_refs() expects page_count(page) == 0 and panics if page_count(page) != 0. To avoid this, we shouldn't touch page_count() if it is zero. This patch uses page_cache_get_speculative() to avoid the panic.
Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> Acked-by: Nick Piggin <npiggin@suse.de>
--- mm/migrate.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-)
Index: b/mm/migrate.c =================================================================== --- a/mm/migrate.c +++ b/mm/migrate.c @@ -243,7 +243,15 @@ void migration_entry_wait(struct mm_stru page = migration_entry_to_page(entry); - get_page(page); + /* + * Once radix-tree replacement of page migration started, page_count + * *must* be zero. And, we don't want to call wait_on_page_locked() + * against a page without get_page(). + * So, we use get_page_unless_zero(), here. Even failed, page fault + * will occur again. + */ + if (!get_page_unless_zero(page)) + goto out; pte_unmap_unlock(ptep, ptl); wait_on_page_locked(page); put_page(page);
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