Hello Michal,
On (06/02/16 11:21), Michal Hocko wrote:
[..]
> > [ 2856.323052] INFO: task cc1:4582 blocked for more than 21 seconds.
> > [ 2856.323055] Not tainted
> > 4.7.0-rc1-next-20160601-dbg-00012-g52c180e-dirty #453
> > [ 2856.323056] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables
> > this message.
> > [ 2856.323059] cc1 D ffff880057e9fd78 0 4582 4575
> > 0x00000000
> > [ 2856.323062] ffff880057e9fd78 ffff880057e08000 ffff880057e9fd90
> > ffff880057ea0000
> > [ 2856.323065] ffff88005dc3dc68 ffffffff00000001 ffff880057e09500
> > ffff88005dc3dc80
> > [ 2856.323067] ffff880057e9fd90 ffffffff81441e33 ffff88005dc3dc68
> > ffff880057e9fe00
> > [ 2856.323068] Call Trace:
> > [ 2856.323074] [<ffffffff81441e33>] schedule+0x83/0x98
> > [ 2856.323077] [<ffffffff81443d9b>] rwsem_down_write_failed+0x18e/0x1d3
> > [ 2856.323080] [<ffffffff810a87cf>] ? unlock_page+0x2b/0x2d
> > [ 2856.323083] [<ffffffff811bdb77>] call_rwsem_down_write_failed+0x17/0x30
> > [ 2856.323084] [<ffffffff811bdb77>] ?
> > call_rwsem_down_write_failed+0x17/0x30
> > [ 2856.323086] [<ffffffff81443630>] down_write+0x1f/0x2e
> > [ 2856.323089] [<ffffffff810ea4f3>] __khugepaged_exit+0x104/0x11a
> > [ 2856.323091] [<ffffffff8103702a>] mmput+0x29/0xc5
> > [ 2856.323093] [<ffffffff8103bbd8>] do_exit+0x34c/0x894
> > [ 2856.323095] [<ffffffff8102f9e0>] ? __do_page_fault+0x2f7/0x399
> > [ 2856.323097] [<ffffffff8103c188>] do_group_exit+0x3c/0x98
> > [ 2856.323099] [<ffffffff8103c1f3>] SyS_exit_group+0xf/0xf
> > [ 2856.323101] [<ffffffff81444cdb>] entry_SYSCALL_64_fastpath+0x13/0x8f
>
> down_write in the exit path is certainly not nice. It is hard to tell
> who is blocking the mmap_sem but it is clear that __khugepaged_exit
> waits for the khugepaged to release its mmap_sem. Do you hapen to have a
> trace of khugepaged? Note that the lock holder might be another writer
> which just hasn't pinned mm_users so khugepaged might be blocked on read
> lock as well. Or khugepaged might be just stuck somewhere...
sorry, no. this is all I have. the kernel was compiled with almost no
debugging functionality enabled (no lockdep, no lock debug, nothing)
for zram performance testing purposes.
I'll try to reproduce the problem; and give your patch some testing.
thanks.
-ss
