Messages in this thread | | | Date | Tue, 17 Apr 2012 08:05:56 -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 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?
Thanx, Paul
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