On Thu, 2008-06-12 at 19:13 -0700, Andrew Morton wrote: > On Fri, 13 Jun 2008 10:44:44 +0900 KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> wrote: > > > This is reproducer of panic. "quick fix" is attached. > > Thanks - I put that in > ftp://ftp.kernel.org/pub/linux/kernel/people/akpm/patches/2.6/2.6.26-rc5/2.6.26-rc5-mm3/hot-fixes/ > > > But I think putback_lru_page() should be re-designed. > > Yes, it sounds that way. Here's a proposed replacement patch that reworks putback_lru_page() slightly and cleans up the call sites. I still want to balance the get_page() in isolate_lru_page() with a put_page() in putback_lru_page() for the primary users--vmscan and page migration. So, I need to drop the lock before the put_page() when handed a page with null mapping and a single reference count as the page will be freed on put_page() and a locked page would bug out in free_pages_check()/bad_page(). Lee PATCH fix page unlocking protocol for putback_lru_page() Against: 2.6.26-rc5-mm3 Replaces Kame-san's hotfix: fix-double-unlock_page-in-2626-rc5-mm3-kernel-bug-at-mm-filemapc-575.patch Applies at end of vmscan/unevictable/mlock series to avoid patch conflicts. 1) modified putback_lru_page() to drop page lock only if both page_mapping() NULL and page_count() == 1 [rather than VM_BUG_ON(page_count(page) != 1]. I want to balance the put_page() from isolate_lru_page() here for vmscan and, e.g., page migration rather than requiring explicit checks of the page_mapping() and explicit put_page() in these areas. However, the page could be truncated while one of these subsystems holds it isolated from the LRU. So, need to handle this case. Callers of putback_lru_page() need to be aware of this and only call it with a page with NULL page_mapping() when they will no longer reference the page afterwards. This is the case for vmscan and page migration. 2) m[un]lock_vma_page() already will not be called for page with NULL mapping. Added VM_BUG_ON() to assert this. 3) modified clear_page_lock() to skip the isolate/putback shuffle for pages with NULL mapping, as they are being truncated/freed. Thus, any future callers of clear_page_lock() need not be concerned about the putback_lru_page() semantics for truncated pages. Signed-off-by: Lee Schermerhorn <lee.schermerhorn@xxxxxx> mm/mlock.c | 29 +++++++++++++++++++---------- mm/vmscan.c | 12 +++++++----- 2 files changed, 26 insertions(+), 15 deletions(-) Index: linux-2.6.26-rc5-mm3/mm/mlock.c =================================================================== --- linux-2.6.26-rc5-mm3.orig/mm/mlock.c 2008-06-12 11:42:59.000000000 -0400 +++ linux-2.6.26-rc5-mm3/mm/mlock.c 2008-06-13 09:47:14.000000000 -0400 @@ -59,27 +59,33 @@ void __clear_page_mlock(struct page *pag dec_zone_page_state(page, NR_MLOCK); count_vm_event(NORECL_PGCLEARED); - if (!isolate_lru_page(page)) { - putback_lru_page(page); - } else { - /* - * Page not on the LRU yet. Flush all pagevecs and retry. - */ - lru_add_drain_all(); - if (!isolate_lru_page(page)) + if (page->mapping) { /* truncated ? */ + if (!isolate_lru_page(page)) { putback_lru_page(page); - else if (PageUnevictable(page)) - count_vm_event(NORECL_PGSTRANDED); + } else { + /* + * Page not on the LRU yet. + * Flush all pagevecs and retry. + */ + lru_add_drain_all(); + if (!isolate_lru_page(page)) + putback_lru_page(page); + else if (PageUnevictable(page)) + count_vm_event(NORECL_PGSTRANDED); + } } } /* * Mark page as mlocked if not already. * If page on LRU, isolate and putback to move to unevictable list. + * + * Called with page locked and page_mapping() != NULL. */ void mlock_vma_page(struct page *page) { BUG_ON(!PageLocked(page)); + VM_BUG_ON(!page_mapping(page)); if (!TestSetPageMlocked(page)) { inc_zone_page_state(page, NR_MLOCK); @@ -92,6 +98,8 @@ void mlock_vma_page(struct page *page) /* * called from munlock()/munmap() path with page supposedly on the LRU. * + * Called with page locked and page_mapping() != NULL. + * * Note: unlike mlock_vma_page(), we can't just clear the PageMlocked * [in try_to_munlock()] and then attempt to isolate the page. We must * isolate the page to keep others from messing with its unevictable @@ -110,6 +118,7 @@ void mlock_vma_page(struct page *page) static void munlock_vma_page(struct page *page) { BUG_ON(!PageLocked(page)); + VM_BUG_ON(!page_mapping(page)); if (TestClearPageMlocked(page)) { dec_zone_page_state(page, NR_MLOCK); Index: linux-2.6.26-rc5-mm3/mm/vmscan.c =================================================================== --- linux-2.6.26-rc5-mm3.orig/mm/vmscan.c 2008-06-12 11:39:09.000000000 -0400 +++ linux-2.6.26-rc5-mm3/mm/vmscan.c 2008-06-13 09:44:44.000000000 -0400 @@ -1,4 +1,4 @@ -/* + /* * linux/mm/vmscan.c * * Copyright (C) 1991, 1992, 1993, 1994 Linus Torvalds @@ -488,6 +488,9 @@ int remove_mapping(struct address_space * lru_lock must not be held, interrupts must be enabled. * Must be called with page locked. * + * If page truncated [page_mapping() == NULL] and we hold the last reference, + * the page will be freed here. For vmscan and page migration. + * * return 1 if page still locked [not truncated], else 0 */ int putback_lru_page(struct page *page) @@ -502,12 +505,11 @@ int putback_lru_page(struct page *page) lru = !!TestClearPageActive(page); was_unevictable = TestClearPageUnevictable(page); /* for page_evictable() */ - if (unlikely(!page->mapping)) { + if (unlikely(!page->mapping && page_count(page) == 1)) { /* - * page truncated. drop lock as put_page() will - * free the page. + * page truncated and we hold last reference. + * drop lock as put_page() will free the page. */ - VM_BUG_ON(page_count(page) != 1); unlock_page(page); ret = 0; } else if (page_evictable(page, NULL)) { -- To unsubscribe from this list: send the line "unsubscribe kernel-testers" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
