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42ef73fe13
On -rt we were seeing spurious bad page states like: Bad page state in process 'firefox' page:c1bc2380 flags:0x40000000 mapping:c1bc2390 mapcount:0 count:0 Trying to fix it up, but a reboot is needed Backtrace: Pid: 503, comm: firefox Not tainted 2.6.26.8-rt13 #3 [<c043d0f3>] ? printk+0x14/0x19 [<c0272d4e>] bad_page+0x4e/0x79 [<c0273831>] free_hot_cold_page+0x5b/0x1d3 [<c02739f6>] free_hot_page+0xf/0x11 [<c0273a18>] __free_pages+0x20/0x2b [<c027d170>] __pte_alloc+0x87/0x91 [<c027d25e>] handle_mm_fault+0xe4/0x733 [<c043f680>] ? rt_mutex_down_read_trylock+0x57/0x63 [<c043f680>] ? rt_mutex_down_read_trylock+0x57/0x63 [<c0218875>] do_page_fault+0x36f/0x88a This is the case where a concurrent fault already installed the PTE and we get to free the newly allocated one. This is due to pgtable_page_ctor() doing the spin_lock_init(&page->ptl) which is overlaid with the {private, mapping} struct. union { struct { unsigned long private; struct address_space *mapping; }; spinlock_t ptl; struct kmem_cache *slab; struct page *first_page; }; Normally the spinlock is small enough to not stomp on page->mapping, but PREEMPT_RT=y has huge 'spin'locks. But lockdep kernels should also be able to trigger this splat, as the lock tracking code grows the spinlock to cover page->mapping. The obvious fix is calling pgtable_page_dtor() like the regular pte free path __pte_free_tlb() does. It seems all architectures except x86 and nm10300 already do this, and nm10300 doesn't seem to use pgtable_page_ctor(), which suggests it doesn't do SMP or simply doesnt do MMU at all or something. Signed-off-by: Peter Zijlstra <a.p.zijlsta@chello.nl> Signed-off-by: Ingo Molnar <mingo@elte.hu> Cc: <stable@kernel.org> |
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