On 10/06/2015 11:23 AM, Kirill A. Shutemov wrote: > This patch adds implementation of split_huge_page() for new > refcountings. > > Unlike previous implementation, new split_huge_page() can fail if > somebody holds GUP pin on the page. It also means that pin on page > would prevent it from bening split under you. It makes situation in > many places much cleaner. > > The basic scheme of split_huge_page(): > > - Check that sum of mapcounts of all subpage is equal to page_count() > plus one (caller pin). Foll off with -EBUSY. This way we can avoid > useless PMD-splits. > > - Freeze the page counters by splitting all PMD and setup migration > PTEs. > > - Re-check sum of mapcounts against page_count(). Page's counts are > stable now. -EBUSY if page is pinned. > > - Split compound page. > > - Unfreeze the page by removing migration entries. > > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> > Tested-by: Sasha Levin <sasha.levin@xxxxxxxxxx> > Tested-by: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxxxxxxx> > Acked-by: Jerome Marchand <jmarchan@xxxxxxxxxx> Hey Kirill, I saw the following while fuzzing: [ 3400.024040] ================================================================== [ 3400.024040] BUG: KASAN: slab-out-of-bounds in unfreeze_page+0x706/0xbf0 at addr ffff880670dbc0c0 [ 3400.024040] Read of size 8 by task run_vmtests/10752 [ 3400.024040] ============================================================================= [ 3400.024040] BUG vm_area_struct (Not tainted): kasan: bad access detected [ 3400.024040] ----------------------------------------------------------------------------- [ 3400.024040] [ 3400.024040] Disabling lock debugging due to kernel taint [ 3400.024040] INFO: Allocated in copy_process+0x2d6d/0x5b00 age=18600 cpu=28 pid=9566 [ 3400.024040] ___slab_alloc+0x434/0x5b0 [ 3400.024040] __slab_alloc.isra.37+0x79/0xd0 [ 3400.024040] kmem_cache_alloc+0x103/0x330 [ 3400.024040] copy_process+0x2d6d/0x5b00 [ 3400.024040] _do_fork+0x180/0xbb0 [ 3400.024040] SyS_clone+0x3c/0x50 [ 3400.024040] tracesys_phase2+0x88/0x8d [ 3400.024040] INFO: Freed in remove_vma+0x170/0x180 age=18613 cpu=10 pid=21787 [ 3400.024040] __slab_free+0x64/0x260 [ 3400.024040] kmem_cache_free+0x1e1/0x3b0 [ 3400.024040] remove_vma+0x170/0x180 [ 3400.024040] exit_mmap+0x30a/0x3c0 [ 3400.024040] mmput+0x98/0x240 [ 3400.024040] do_exit+0xbe5/0x2830 [ 3400.024040] do_group_exit+0x1b5/0x300 [ 3400.024040] SyS_exit_group+0x22/0x30 [ 3400.024040] tracesys_phase2+0x88/0x8d [ 3400.024040] INFO: Slab 0xffffea0019c36f00 objects=33 used=33 fp=0x (null) flags=0x12fffff80004080 [ 3400.024040] INFO: Object 0xffff880670dbc000 @offset=0 fp=0x00007f6bff4e7000 [ 3400.024040] [ 3400.024040] Object ffff880670dbc000: 00 70 4e ff 6b 7f 00 00 00 90 80 ff 6b 7f 00 00 .pN.k.......k... [ 3400.024040] Object ffff880670dbc010: f0 e0 db 70 06 88 ff ff e0 03 80 02 18 88 ff ff ...p............ [ 3400.024040] Object ffff880670dbc020: 01 04 80 02 18 88 ff ff 00 00 00 00 00 00 00 00 ................ [ 3400.024040] Object ffff880670dbc030: 00 00 00 00 00 00 00 00 00 70 ce 7e 3f 7f 00 00 .........p.~?... [ 3400.024040] Object ffff880670dbc040: 00 f0 83 a6 06 88 ff ff 25 00 00 00 00 00 00 80 ........%....... [ 3400.024040] Object ffff880670dbc050: 73 00 10 08 00 00 00 00 00 00 00 00 00 00 00 00 s............... [ 3400.024040] Object ffff880670dbc060: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ [ 3400.024040] Object ffff880670dbc070: 00 00 00 00 00 00 00 00 90 dc cf a4 06 88 ff ff ................ [ 3400.024040] Object ffff880670dbc080: 10 d8 cf a4 06 88 ff ff b8 d1 ee 24 08 88 ff ff ...........$.... [ 3400.024040] Object ffff880670dbc090: 00 00 00 00 00 00 00 00 e7 f4 bf f6 07 00 00 00 ................ [ 3400.024040] Object ffff880670dbc0a0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ [ 3400.024040] Object ffff880670dbc0b0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ [ 3400.024040] CPU: 20 PID: 10752 Comm: run_vmtests Tainted: G B 4.3.0-next-20151115-sasha-00042-g0f5ce29 #2641 [ 3400.024040] 0000000000000014 0000000076bf224e ffff880ef1b7ee70 ffffffffabe427db [ 3400.024040] ffff880182342000 ffff880670dbc000 ffff880670dbc000 ffff880ef1b7eea0 [ 3400.024040] ffffffffaa792a7a ffff880182342000 ffffea0019c36f00 ffff880670dbc000 [ 3400.024040] Call Trace: [ 3400.024040] dump_stack (lib/dump_stack.c:52) [ 3400.024040] print_trailer (mm/slub.c:655) [ 3400.024040] object_err (mm/slub.c:662) [ 3400.024040] kasan_report_error (mm/kasan/report.c:138 mm/kasan/report.c:236) [ 3400.024040] __asan_report_load8_noabort (mm/kasan/report.c:280) [ 3400.024040] unfreeze_page (mm/huge_memory.c:3062 mm/huge_memory.c:3099) [ 3400.024040] split_huge_page_to_list (include/linux/compiler.h:218 mm/huge_memory.c:3208 mm/huge_memory.c:3291) [ 3400.024040] deferred_split_scan (mm/huge_memory.c:3378) [ 3400.024040] shrink_slab (mm/vmscan.c:352 mm/vmscan.c:444) [ 3400.024040] shrink_zone (mm/vmscan.c:2444) [ 3400.024040] do_try_to_free_pages (mm/vmscan.c:2595 mm/vmscan.c:2645) [ 3400.024040] try_to_free_pages (mm/vmscan.c:2853) [ 3400.024040] __alloc_pages_nodemask (mm/page_alloc.c:2864 mm/page_alloc.c:2882 mm/page_alloc.c:3150 mm/page_alloc.c:3261) [ 3400.024040] alloc_fresh_huge_page (include/linux/gfp.h:415 include/linux/gfp.h:428 mm/hugetlb.c:1330 mm/hugetlb.c:1348) [ 3400.024040] __nr_hugepages_store_common (include/linux/spinlock.h:302 mm/hugetlb.c:2164 mm/hugetlb.c:2279) [ 3400.024040] hugetlb_sysctl_handler_common (mm/hugetlb.c:2784) [ 3400.024040] hugetlb_sysctl_handler (mm/hugetlb.c:2796) [ 3400.024040] proc_sys_call_handler (fs/proc/proc_sysctl.c:543) [ 3400.024040] proc_sys_write (fs/proc/proc_sysctl.c:562) [ 3400.024040] __vfs_write (fs/read_write.c:489) [ 3400.024040] vfs_write (fs/read_write.c:538) [ 3400.024040] SyS_write (fs/read_write.c:585 fs/read_write.c:577) [ 3400.024040] tracesys_phase2 (arch/x86/entry/entry_64.S:273) [ 3400.024040] Memory state around the buggy address: [ 3400.024040] ffff880670dbbf80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 [ 3400.024040] ffff880670dbc000: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 [ 3400.024040] >ffff880670dbc080: 00 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc [ 3400.024040] ^ [ 3400.024040] ffff880670dbc100: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc [ 3400.024040] ffff880670dbc180: fc fc fc fc fc fc fc fc fc fc fc fc fc fc 00 00 [ 3400.024040] ================================================================== Thanks, Sasha -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. 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