Lee Schermerhorn wrote: > 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. > Hi Lee, Thanks, After applying the patch, the kernel does not panic's while bootup. Tested-by: Kamalesh Babulal <kamalesh@xxxxxxxxxxxxxxxxxx> > 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)) { > > -- Thanks & Regards, Kamalesh Babulal, Linux Technology Center, IBM, ISTL. -- 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
