Messages in this thread | | | Date | Sat, 20 Jun 2009 20:26:08 +0100 | From | Mel Gorman <> | Subject | Re: [BUG] Bad page flags when process using mlock()ed memory exits |
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On Fri, Jun 19, 2009 at 07:45:02PM +0200, Johannes Weiner wrote: > On Fri, Jun 19, 2009 at 02:11:21PM +1000, Peter Chubb wrote: > > > > In recent kernels I've been seeing many mesages of the form: > > > > BUG: Bad page state in process reiserfsck pfn:79c58 > > page:c3d03b00 flags:8050000c count:0 mapcount:0 mapping:(null) index:8095 > > Pid: 3927, comm: reiserfsck Not tainted 2.6.30-test-05456-gda456f1 #60 > > Call Trace: > > [<c134a67c>] ? printk+0xf/0x13 > > [<c10774dc>] bad_page+0xc9/0xe2 > > [<c1078041>] free_hot_cold_page+0x5c/0x204 > > [<c1078206>] __pagevec_free+0x1d/0x25 > > [<c107ac3e>] release_pages+0x14e/0x18e) > > [<c108ef8a>] free_pages_and_swap_cache+0x69/0x82 > > [<c1089458>] exit_mmap+0xf6/0x11f > > [<c102afcd>] mmput+0x39/0xaf > > [<c102e534>] exit_mm+0xe5/0xed > > [<c102fa66>] do_exit+0x13f/0x578 > > [<c102fefd>] do_group_exit+0x5e/0x85 > > [<c102ff37>] sys_exit_group+0x13/0x17 > > [<c10031ef>] sysenter_do_call+0x12/0x3c > > Disabling lock debugging due to kernel taint > > > > This appears to have been introduced by patch > > da456f14d2f2d7350f2b9440af79c85a34c7eed5 > > page allocator: do not disable interrupts in free_page_mlock() > > > > That patch removed the free_page_mlock() from free_pages_check(), so > > if free_hot_cold_page() is called on an Mlocked page (e.g., if a > > process that used mlock() calls exit()) free_pages_check() will always > > barf, whereas before it would just unlock the page. > > I prepared a fix, thanks for chasing it down. > > Mel, to keep this simple I just used the atomic test-clear, but if I > am not mistaken we should not need any atomicity here, so we could > probably add a __TestClearPage version and use this instead...? >
It should not need to be atomic as there should be no other user of the page. If __TestClearPage existed, it would be usable here.
> --- > From 493b74e8615db4e3323b5b169b0b8265dfd7c3f4 Mon Sep 17 00:00:00 2001 > From: Johannes Weiner <hannes@cmpxchg.org> > Date: Fri, 19 Jun 2009 19:30:56 +0200 > Subject: [patch] mm: page_alloc: clear PG_locked before checking flags on free > > da456f1 "page allocator: do not disable interrupts in free_page_mlock()" moved > the PG_mlocked clearing after the flag sanity checking which makes mlocked > pages always trigger 'bad page'. Fix this by clearing the bit up front. > > Reported-by: Peter Chubb <peter.chubb@nicta.com.au> > Debugged-by: Peter Chubb <peter.chubb@nicta.com.au> > Signed-off-by: Johannes Weiner <hannes@cmpxchg.org> > Cc: Mel Gorman <mel@csn.ul.ie>
The patch looks ok and I see no problem with clearing the bit without disabling interrupts. The disabling of interrupts was for updating the counters so;
Acked-by: Mel Gorman <mel@csn.ul.ie>
Thanks Peter for catching this and thanks Johannes for fixing it up.
My apologies for the long delay in responding. I was offline for two days at a conference. I thought I would have internet access but no such luck. Am playing catch-up now in a rush.
> --- > mm/page_alloc.c | 9 ++++----- > 1 files changed, 4 insertions(+), 5 deletions(-) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 6f0753f..30d5093 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -488,7 +488,6 @@ static inline void __free_one_page(struct page *page, > */ > static inline void free_page_mlock(struct page *page) > { > - __ClearPageMlocked(page); > __dec_zone_page_state(page, NR_MLOCK); > __count_vm_event(UNEVICTABLE_MLOCKFREED); > } > @@ -558,7 +557,7 @@ static void __free_pages_ok(struct page *page, unsigned int order) > unsigned long flags; > int i; > int bad = 0; > - int clearMlocked = PageMlocked(page); > + int wasMlocked = TestClearPageMlocked(page); > > kmemcheck_free_shadow(page, order); > > @@ -576,7 +575,7 @@ static void __free_pages_ok(struct page *page, unsigned int order) > kernel_map_pages(page, 1 << order, 0); > > local_irq_save(flags); > - if (unlikely(clearMlocked)) > + if (unlikely(wasMlocked)) > free_page_mlock(page); > __count_vm_events(PGFREE, 1 << order); > free_one_page(page_zone(page), page, order, > @@ -1022,7 +1021,7 @@ static void free_hot_cold_page(struct page *page, int cold) > struct zone *zone = page_zone(page); > struct per_cpu_pages *pcp; > unsigned long flags; > - int clearMlocked = PageMlocked(page); > + int wasMlocked = TestClearPageMlocked(page); > > kmemcheck_free_shadow(page, 0); > > @@ -1041,7 +1040,7 @@ static void free_hot_cold_page(struct page *page, int cold) > pcp = &zone_pcp(zone, get_cpu())->pcp; > set_page_private(page, get_pageblock_migratetype(page)); > local_irq_save(flags); > - if (unlikely(clearMlocked)) > + if (unlikely(wasMlocked)) > free_page_mlock(page); > __count_vm_event(PGFREE); > > -- > 1.6.3 > > >
-- Mel Gorman Part-time Phd Student Linux Technology Center University of Limerick IBM Dublin Software Lab
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