Messages in this thread | | | Date | Tue, 17 Apr 2012 08:53:16 -0700 | From | "Paul E. McKenney" <> | Subject | Re: New RCU related warning due to rcu_preempt_depth() changes |
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On Tue, Apr 17, 2012 at 05:36:59PM +0200, Sasha Levin wrote: > On Tue, Apr 17, 2012 at 5:05 PM, Paul E. McKenney > <paulmck@linux.vnet.ibm.com> wrote: > > On Tue, Apr 17, 2012 at 10:42:47AM +0200, Sasha Levin wrote: > >> Hi Paul, > >> > >> It looks like commit 7298b03 ("rcu: Move __rcu_read_lock() and > >> __rcu_read_unlock() to per-CPU variables") is causing the following > >> warning (I've added the extra fields on the second line): > >> > >> [ 77.330920] BUG: sleeping function called from invalid context at > >> mm/memory.c:3933 > >> [ 77.336571] in_atomic(): 0, irqs_disabled(): 0, preempt count: 0, > >> preempt offset: 0, rcu depth: 1, pid: 5669, name: trinity > >> [ 77.344135] no locks held by trinity/5669. > >> [ 77.349644] Pid: 5669, comm: trinity Tainted: G W > >> 3.4.0-rc3-next-20120417-sasha-dirty #83 > >> [ 77.354401] Call Trace: > >> [ 77.355956] [<ffffffff810e83f3>] __might_sleep+0x1f3/0x210 > >> [ 77.358811] [<ffffffff81198eaf>] might_fault+0x2f/0xa0 > >> [ 77.361997] [<ffffffff810e3228>] schedule_tail+0x88/0xb0 > >> [ 77.364671] [<ffffffff826a01d3>] ret_from_fork+0x13/0x80 > >> > >> As you can see, rcu_preempt_depth() returns 1 when running in that > >> context, which looks pretty odd. > > > > Ouch!!! > > > > So it looks like I missed a place where I need to save and restore > > the new per-CPU rcu_read_lock_nesting and rcu_read_unlock_special > > variables. My (probably hopelessly naive) guess is that I need to add > > a rcu_switch_from() and rcu_switch_to() into schedule_tail(), but to > > make rcu_switch_from() take the task_struct pointer as an argument, > > passing in prev. > > > > Does this make sense, or am I still missing something here? > > I've let the test run for a bit more, and it appears that I'm getting > this warning from lots of different sources, would this > schedule_tail() fix all of them?
If I understand the failure correctly, yes. If the task switches without RCU paying attention, the nesting count for both the outgoing and the incoming tasks can get messed up. The messed-up counts could easily cause problems downstream.
Of course, there might well be additional bugs.
I will put a speculative patch together and send it along.
Thanx, Paul
> Here's several traces for reference: > > [ 223.068875] [<ffffffff810e83f3>] __might_sleep+0x1f3/0x210 > [ 223.070719] [<ffffffff810b2a05>] close_files+0x1d5/0x220 > [ 223.072531] [<ffffffff810b2830>] ? find_new_reaper+0x230/0x230 > [ 223.076325] [<ffffffff810b4811>] put_files_struct+0x21/0x1b0 > [ 223.080649] [<ffffffff8269eb20>] ? _raw_spin_unlock+0x30/0x60 > [ 223.084455] [<ffffffff810b4a5d>] exit_files+0x4d/0x60 > [ 223.087967] [<ffffffff810b51ac>] do_exit+0x28c/0x470 > [ 223.091369] [<ffffffff810e44d1>] ? get_parent_ip+0x11/0x50 > [ 223.093190] [<ffffffff810b5473>] do_group_exit+0xa3/0xe0 > [ 223.095061] [<ffffffff810c4759>] get_signal_to_deliver+0x389/0x400 > [ 223.098400] [<ffffffff8104bce2>] do_signal+0x42/0x120 > [ 223.100222] [<ffffffff8104c4d7>] ? do_divide_error+0xa7/0xb0 > [ 223.102267] [<ffffffff8269fa7f>] ? retint_signal+0x11/0x92 > [ 223.104145] [<ffffffff8104be34>] do_notify_resume+0x54/0xa0 > [ 223.106033] [<ffffffff8269fabb>] retint_signal+0x4d/0x92 > > [ 176.217632] [<ffffffff810e83f3>] __might_sleep+0x1f3/0x210 > [ 176.223583] [<ffffffff81081b83>] do_page_fault+0x243/0x4f0 > [ 176.229932] [<ffffffff811151ca>] ? __lock_release+0x1ba/0x1d0 > [ 176.233651] [<ffffffff8269ec1b>] ? _raw_spin_unlock_irq+0x2b/0x80 > [ 176.239389] [<ffffffff810e44d1>] ? get_parent_ip+0x11/0x50 > [ 176.242507] [<ffffffff810e469e>] ? sub_preempt_count+0xae/0xe0 > [ 176.248795] [<ffffffff8269ec41>] ? _raw_spin_unlock_irq+0x51/0x80 > [ 176.255454] [<ffffffff81079e51>] do_async_page_fault+0x31/0xa0 > [ 176.260342] [<ffffffff8269fcd5>] async_page_fault+0x25/0x30 > > [ 173.587864] [<ffffffff810e83f3>] __might_sleep+0x1f3/0x210 > [ 173.593134] [<ffffffff811f5542>] ? __d_alloc+0x32/0x1a0 > [ 173.603730] [<ffffffff811c0f8d>] kmem_cache_alloc+0x4d/0x160 > [ 173.604746] [<ffffffff811f5e40>] ? __d_lookup_rcu+0x240/0x240 > [ 173.608932] [<ffffffff811f5542>] __d_alloc+0x32/0x1a0 > [ 173.612444] [<ffffffff811f56f3>] d_alloc+0x23/0x80 > [ 173.616887] [<ffffffff811e773b>] __lookup_hash+0x9b/0x110 > [ 173.621488] [<ffffffff811e77c4>] lookup_hash+0x14/0x20 > [ 173.624395] [<ffffffff811ecc99>] do_unlinkat+0x79/0x1e0 > [ 173.626483] [<ffffffff8269ec41>] ? _raw_spin_unlock_irq+0x51/0x80 > [ 173.632242] [<ffffffff826a02e9>] ? sysret_check+0x22/0x5d > [ 173.637884] [<ffffffff8186db5e>] ? trace_hardirqs_on_thunk+0x3a/0x3f > [ 173.642176] [<ffffffff811ece51>] sys_unlink+0x11/0x20 > [ 173.645320] [<ffffffff826a02bd>] system_call_fastpath+0x1a/0x1f >
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