Messages in this thread Patch in this message | | | Date | Thu, 20 Jan 2005 21:34:17 +0800 | From | zhan rongkai <> | Subject | [PATCH]: fix the bug of __free_pages() of mm/page_alloc.c |
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[PATCH]: fix the bug of __free_pages() of mm/page_alloc.c =========================================================
The buddy allocator's __free_pages() function seems to be buggy.
The following codes are from kernel 2.6.10:
fastcall void __free_pages(struct page *page, unsigned int order) { if (!PageReserved(page) && put_page_testzero(page)) { if (order == 0) free_hot_page(page); else __free_pages_ok(page, order); } }
As you know, before truely freeing all pages, this function calls put_page_testzero(page) to drop the refcount of the pages.
But, in fact the macro put_page_testzero(page) **only** drops **one** page's refcount. Therefore, if (order > 0), the refcounts of (page+1) .. (page+(1<<order)-1) are unchanged! This will cause __free_pages_ok() to dump stack, because it finds some pages' page_count() are not zero!
The following is the OOPS of this bug (I make kernel print verbose info):
slab cache: size-32768 is to be destroyed! __free_pages: order=3, we are freeing page: 001d8740-001d8858 page 001d8740 count: 1 page 001d8768 count: 1 page 001d8790 count: 1 page 001d87b8 count: 1 page 001d87e0 count: 1 page 001d8808 count: 1 page 001d8830 count: 1 page 001d8858 count: 1 put_page_testzero() has been called! page 001d8740 count: 0 page 001d8768 count: 1 page 001d8790 count: 1 page 001d87b8 count: 1 page 001d87e0 count: 1 page 001d8808 count: 1 page 001d8830 count: 1 page 001d8858 count: 1 Bad page state at __free_pages_ok (in process 'hello', mem_map 00139000, order 3, page 001d8768, i 1) flags:0x20000000 mapping:00000000 mapped:0 count:1 Backtrace: Call Trace: [<00034b9c>] __free_pages_ok+0x12c/0x1f0 [<000358d0>] __free_pages+0xd0/0x1a0 [<000359f4>] free_pages+0x54/0x70 [<00038df4>] slab_destroy+0x114/0x1e0 [<0003a0b4>] reap_timer_fnc+0x194/0x300 [<0001e058>] do_timer+0x58/0x600 [<0001de7c>] run_timer_softirq+0x10c/0x200 [<0001ace4>] do_softirq+0xb4/0x140 [<00124548>] init_bio+0x8/0x200 [<0000be68>] do_IRQ+0x208/0x280 [<00124548>] init_bio+0x8/0x200 [<000e22f8>] handle_IRQ+0x58/0x60 [<000d7344>] blkdev_ioctl+0x304/0x8f0 [<00122ca0>] free_bootmem_core+0xa0/0xf0 [<00124548>] init_bio+0x8/0x200 [<0001101c>] try_to_wake_up+0x14c/0x250 [<00011140>] wake_up_process+0x20/0x30 [<000370a0>] pdflush_operation+0xc0/0xe0 [<00036ab4>] wb_timer_fn+0x24/0x70 [<0001de7c>] run_timer_softirq+0x10c/0x200 [<00123a88>] free_area_init_node+0x158/0x450 [<00090bb8>] group_reserve_blocks+0x8/0x90 [<0000ee00>] do_gettimeofday+0xb0/0x160 ......
Please confirm me! This is a patch to fix this bug: ---------------------------------------------------
--- linux-2.6.10.orig/mm/page_alloc.c 2004-12-25 05:33:51.000000000 +0800 +++ linux-2.6.10/mm/page_alloc.c 2005-01-20 21:31:07.000000000 +0800 @@ -786,9 +786,19 @@ free_hot_cold_page(pvec->pages[i], pvec->cold); } +static inline int drop_pages_testzero(struct page *page, unsigned int order) +{ + int i, ret = 1; + struct page *pg = page; + + for (i = 0; i < (1 << order); i++, pg++) + ret &= put_page_testzero(pg); + return ret; +} + fastcall void __free_pages(struct page *page, unsigned int order) { - if (!PageReserved(page) && put_page_testzero(page)) { + if (!PageReserved(page) && drop_pages_testzero(page, order)) { if (order == 0) free_hot_page(page); else
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