Re: mm: shmem: freeing mlocked page

[Sasha Levin]

On 11/06/2014 11:27 PM, Sasha Levin wrote:
> Hi all,
> 
> While fuzzing with trinity inside a KVM tools guest running the latest -next
> kernel, I've stumbled on the following spew:
> 
> [ 1441.564471] BUG: Bad page state in process trinity-c612  pfn:12593a
> [ 1441.564476] page:ffffea0006e175c0 count:0 mapcount:0 mapping:          (null) index:
> 0x49
> [ 1441.564488] flags: 0xafffff8028000c(referenced|uptodate|swapbacked|mlocked)
> [ 1441.564491] page dumped because: PAGE_FLAGS_CHECK_AT_FREE flag(s) set
> [ 1441.564493] bad because of flags:
> [ 1441.564498] flags: 0x200000(mlocked)
> [ 1441.564503] Modules linked in:
> [ 1441.564511] CPU: 2 PID: 11657 Comm: trinity-c612 Not tainted 3.18.0-rc3-next-20141106-sasha-00054-g09b7ccf-dirty #1447
> [ 1441.564519]  0000000000000000 0000000000000000 1ffffffff3b44e48 ffff8805c969b868
> [ 1441.564526]  ffffffff9c085024 0000000000000000 ffffea0006e175c0 ffff8805c969b898
> [ 1441.564532]  ffffffff925fd0a1 ffffea0006e17628 dfffe90000000000 0000000000000000
> [ 1441.564534] Call Trace:
> [ 1441.568496] dump_stack (lib/dump_stack.c:52)
> [ 1441.568516] bad_page (mm/page_alloc.c:338)
> [ 1441.568523] free_pages_prepare (mm/page_alloc.c:649 mm/page_alloc.c:755)
> [ 1441.568531] free_hot_cold_page (mm/page_alloc.c:1436)
> [ 1441.568541] free_hot_cold_page_list (mm/page_alloc.c:1482 (discriminator 3))
> [ 1441.568555] release_pages (mm/swap.c:961)
> [ 1441.568566] __pagevec_release (include/linux/pagevec.h:44 mm/swap.c:978)
> [ 1441.568579] shmem_undo_range (include/linux/pagevec.h:69 mm/shmem.c:451)
> [ 1441.568591] shmem_truncate_range (mm/shmem.c:546)
> [ 1441.568599] shmem_fallocate (include/linux/spinlock.h:309 mm/shmem.c:2092)
> [ 1441.568612] ? __sb_start_write (fs/super.c:1208)
> [ 1441.568622] ? __sb_start_write (fs/super.c:1208)
> [ 1441.568633] do_fallocate (fs/open.c:297)
> [ 1441.568648] SyS_madvise (mm/madvise.c:332 mm/madvise.c:381 mm/madvise.c:531 mm/madvise.c:462)
> [ 1441.568660] ? syscall_trace_enter_phase1 (include/linux/context_tracking.h:27 arch/x86/kernel/ptrace.c:1486)
> [ 1441.568672] tracesys_phase2 (arch/x86/kernel/entry_64.S:529)
> 
> I'm slightly confused here, because the page is mapcount==0, not LOCKED but still MLOCKED...

So I got this as well:

[ 1026.988043] BUG: Bad page state in process trinity-c374  pfn:23f70
[ 1026.989684] page:ffffea0000b3d300 count:0 mapcount:0 mapping:          (null) index:0x5b
[ 1026.991151] flags: 0x1fffff8028000c(referenced|uptodate|swapbacked|mlocked)
[ 1026.992410] page dumped because: PAGE_FLAGS_CHECK_AT_FREE flag(s) set
[ 1026.993479] bad because of flags:
[ 1026.994125] flags: 0x200000(mlocked)
[ 1026.994816] Modules linked in:
[ 1026.995378] CPU: 7 PID: 7879 Comm: trinity-c374 Not tainted 3.18.0-rc4-next-20141113-sasha-00047-gd1763ce-dirty #1455
[ 1026.996123] FAULT_INJECTION: forcing a failure.
[ 1026.996123] name failslab, interval 100, probability 30, space 0, times -1
[ 1026.999050]  0000000000000000 0000000000000000 0000000000b3d300 ffff88061295bbd8
[ 1027.000676]  ffffffff92f71097 0000000000000000 ffffea0000b3d300 ffff88061295bc08
[ 1027.002020]  ffffffff8197ef7a ffffea0000b3d300 ffffffff942dd148 dfffe90000000000
[ 1027.003359] Call Trace:
[ 1027.003831] dump_stack (lib/dump_stack.c:52)
[ 1027.004725] bad_page (mm/page_alloc.c:338)
[ 1027.005623] free_pages_prepare (mm/page_alloc.c:657 mm/page_alloc.c:763)
[ 1027.006761] free_hot_cold_page (mm/page_alloc.c:1438)
[ 1027.007772] ? __page_cache_release (mm/swap.c:66)
[ 1027.008815] put_page (mm/swap.c:270)
[ 1027.009665] page_cache_pipe_buf_release (fs/splice.c:93)
[ 1027.010888] __splice_from_pipe (fs/splice.c:784 fs/splice.c:886)
[ 1027.011917] ? might_fault (./arch/x86/include/asm/current.h:14 mm/memory.c:3734)
[ 1027.012856] ? pipe_lock (fs/pipe.c:69)
[ 1027.013728] ? write_pipe_buf (fs/splice.c:1534)
[ 1027.014756] vmsplice_to_user (fs/splice.c:1574)
[ 1027.015725] ? rcu_read_lock_held (kernel/rcu/update.c:169)
[ 1027.016757] ? __fget_light (include/linux/fdtable.h:80 fs/file.c:684)
[ 1027.017782] SyS_vmsplice (fs/splice.c:1656 fs/splice.c:1639)
[ 1027.018863] tracesys_phase2 (arch/x86/kernel/entry_64.S:529)

Which makes me suspect I blamed shmem for nothing.


Thanks,
Sasha

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