LKML: "Paul E. McKenney": Re: [PATCH rcu/urgent 0/6] Fixes for RCU/scheduler/irq-threads trainwreck

On Tue, Jul 19, 2011 at 10:07:32PM -0400, Ed Tomlinson wrote:
> On Tuesday 19 July 2011 21:30:00 Ed Tomlinson wrote:
> > On Tuesday 19 July 2011 20:17:38 Paul E. McKenney wrote:
>
> Paul,
>
> Two things to add. Its possible an eariler error is missing from the log below. My serial console was missing
> entries from before '0 and 40ish' and I did think I saw a bunch of FFFFFFFs scroll by eariler...
>
> Second, booting with threadirqs and boost enabled in .config with patches 2,5,6 is ok so far.

Patches 3 and 4 resulted in failures? (Patch 1 certainly did.)

Thanx, Paul

> Thanks,
> Ed
>
> > Pulling this on top of master and rebuilding with boost enabled and booting with threadirqs does not
> > boot correctly here.
> >
> > * Starting APC UPS daemon ...
> > [ 46.007217]
> > [ 46.007221] =================================
> > [ 46.008013] [ INFO: inconsistent lock state ]
> > [ 46.008013] 3.0.0-rc7-crc+ #340
> > [ 46.008013] ---------------------------------
> > [ 46.008013] inconsistent {IN-SOFTIRQ-W} -> {SOFTIRQ-ON-W} usage.
> > [ 46.008013] ip/2982 [HC0[0]:SC0[0]:HE1:SE1] takes:
> > [ 46.008013] (rcu_node_level_0){+.?...}, at: [<ffffffff810ba279>] rcu_report_exp_rnp+0x19/0x50
> > [ 46.008013] {IN-SOFTIRQ-W} state was registered at:
> > [ 46.008013] [<ffffffff8108a1e5>] __lock_acquire+0x5a5/0x16a0
> > [ 46.008013] [<ffffffff8108b8d5>] lock_acquire+0x95/0x140
> > [ 46.008013] [<ffffffff815793a6>] _raw_spin_lock_irqsave+0x46/0x60
> > [ 46.008013] [<ffffffff810bbf80>] __rcu_process_callbacks+0x190/0x2a0
> > [ 46.008013] [<ffffffff810bc0ed>] rcu_process_callbacks+0x5d/0x60
> > [ 46.008013] [<ffffffff81052e14>] __do_softirq+0x194/0x300
> > [ 46.008013] [<ffffffff8105311d>] run_ksoftirqd+0x19d/0x240
> > [ 46.008013] [<ffffffff81071296>] kthread+0xb6/0xc0
> > [ 46.008013] [<ffffffff81582294>] kernel_thread_helper+0x4/0x10
> > [ 46.008013] irq event stamp: 6802
> > [ 46.008013] hardirqs last enabled at (6801): [<ffffffff815776bd>] __mutex_unlock_slowpath+0x10d/0x1c0
> > [ 46.008013] hardirqs last disabled at (6802): [<ffffffff8157937c>] _raw_spin_lock_irqsave+0x1c/0x60
> > [ 46.008013] softirqs last enabled at (6698): [<ffffffff814c274a>] sk_common_release+0x6a/0x120
> > [ 46.008013] softirqs last disabled at (6696): [<ffffffff81579476>] _raw_write_lock_bh+0x16/0x50
> > [ 46.008013]
> > [ 46.008013] other info that might help us debug this:
> > [ 46.008013] Possible unsafe locking scenario:
> > [ 46.008013]
> > [ 46.008013] CPU0
> > [ 46.008013] ----
> > [ 46.008013] lock(rcu_node_level_0);
> > [ 46.008013] <Interrupt>
> > [ 46.008013] lock(rcu_node_level_0);
> > [ 46.008013]
> > [ 46.008013] *** DEADLOCK ***
> > [ 46.008013]
> > [ 46.008013] 3 locks held by ip/2982:
> > [ 46.008013] #0: (rtnl_mutex){+.+.+.}, at: [<ffffffff814e4fd7>] rtnl_lock+0x17/0x20
> > [ 46.008013] #1: (sync_rcu_preempt_exp_mutex){+.+...}, at: [<ffffffff810bc9e7>] synchronize_rcu_expedited+0x37/0x210
> > [ 46.008013] #2: (rcu_node_level_0){+.?...}, at: [<ffffffff810ba279>] rcu_report_exp_rnp+0x19/0x50
> > [ 46.008013]
> > [ 46.008013] stack backtrace:
> > [ 46.008013] Pid: 2982, comm: ip Tainted: G W 3.0.0-rc7-crc+ #340
> > [ 46.008013] Call Trace:
> > [ 46.008013] [<ffffffff81088c33>] print_usage_bug+0x223/0x270
> > [ 46.008013] [<ffffffff81089558>] mark_lock+0x328/0x400
> > [ 46.008013] [<ffffffff8108969e>] mark_held_locks+0x6e/0xa0
> > [ 46.008013] [<ffffffff81579a5d>] ? _raw_spin_unlock_irqrestore+0x7d/0x90
> > [ 46.008013] [<ffffffff8108999d>] trace_hardirqs_on_caller+0x14d/0x190
> > [ 46.008013] [<ffffffff810899ed>] trace_hardirqs_on+0xd/0x10
> > [ 46.008013] [<ffffffff81579a5d>] _raw_spin_unlock_irqrestore+0x7d/0x90
> > [ 46.008013] [<ffffffff810bcb18>] synchronize_rcu_expedited+0x168/0x210
> > [ 46.008013] [<ffffffff8111a073>] ? might_fault+0x53/0xb0
> > [ 46.008013] [<ffffffff8125200a>] ? security_capable+0x2a/0x30
> > [ 46.008013] [<ffffffff814d0985>] synchronize_net+0x45/0x50
> > [ 46.008013] [<ffffffffa0359613>] ipip6_tunnel_ioctl+0x5f3/0x800 [sit]
> > [ 46.008013] [<ffffffffa0359020>] ? ipip6_tunnel_locate+0x2e0/0x2e0 [sit]
> > [ 46.008013] [<ffffffff814d43ba>] dev_ifsioc+0x11a/0x2c0
> > [ 46.008013] [<ffffffff814d678a>] dev_ioctl+0x35a/0x810
> > [ 46.008013] [<ffffffff81089a8d>] ? debug_check_no_locks_freed+0x9d/0x150
> > [ 46.008013] [<ffffffff8108999d>] ? trace_hardirqs_on_caller+0x14d/0x190
> > [ 46.008013] [<ffffffff810899ed>] ? trace_hardirqs_on+0xd/0x10
> > [ 46.008013] [<ffffffff814bb83a>] sock_ioctl+0xea/0x2b0
> > [ 46.008013] [<ffffffff81162474>] do_vfs_ioctl+0xa4/0x5a0
> > [ 46.008013] [<ffffffff815799cc>] ? _raw_spin_unlock+0x5c/0x70
> > [ 46.008013] [<ffffffff8114c1cc>] ? fd_install+0x7c/0x90
> > [ 46.008013] [<ffffffff8158149c>] ? sysret_check+0x27/0x62
> > [ 46.008013] [<ffffffff81162a09>] sys_ioctl+0x99/0xa0
> > [ 46.008013] [<ffffffff8158146b>] system_call_fastpath+0x16/0x1b
> > [ 46.786123] BUG: sleeping function called from invalid context at net/ipv4/route.c:757
> > [ 46.799548] in_atomic(): 1, irqs_disabled(): 0, pid: 2982, name: ip
> > [ 46.799553] INFO: lockdep is turned off.
> > [ 46.799561] Pid: 2982, comm: ip Tainted: G W 3.0.0-rc7-crc+ #340
> > [ 46.799565] Call Trace:
> > [ 46.799576] [<ffffffff81036b39>] __might_sleep+0xf9/0x120
> > [ 46.799586] [<ffffffff814fea38>] rt_do_flush+0x178/0x1b0
> > [ 46.799594] [<ffffffff814feafc>] rt_cache_flush+0x5c/0x70
> > [ 46.799606] [<ffffffff81542d92>] fib_netdev_event+0x72/0xf0
> > [ 46.799615] [<ffffffff8157d576>] notifier_call_chain+0x56/0x80
> > [ 46.799625] [<ffffffff81077ff6>] raw_notifier_call_chain+0x16/0x20
> > [ 46.799633] [<ffffffff814d1cd4>] call_netdevice_notifiers+0x74/0x90
> > [ 46.799642] [<ffffffff814d2c37>] netdev_state_change+0x27/0x40
> > [ 46.799653] [<ffffffffa0359686>] ipip6_tunnel_ioctl+0x666/0x800 [sit]
> > [ 46.799663] [<ffffffffa0359020>] ? ipip6_tunnel_locate+0x2e0/0x2e0 [sit]
> > [ 46.799673] [<ffffffff814d43ba>] dev_ifsioc+0x11a/0x2c0
> > [ 46.799682] [<ffffffff814d678a>] dev_ioctl+0x35a/0x810
> > [ 46.799690] [<ffffffff81089a8d>] ? debug_check_no_locks_freed+0x9d/0x150
> > [ 46.799700] [<ffffffff8108999d>] ? trace_hardirqs_on_caller+0x14d/0x190
> > [ 46.799707] [<ffffffff810899ed>] ? trace_hardirqs_on+0xd/0x10
> > [ 46.799718] [<ffffffff814bb83a>] sock_ioctl+0xea/0x2b0
> > [ 46.799726] [<ffffffff81162474>] do_vfs_ioctl+0xa4/0x5a0
> > [ 46.799735] [<ffffffff815799cc>] ? _raw_spin_unlock+0x5c/0x70
> > [ 46.799744] [<ffffffff8114c1cc>] ? fd_install+0x7c/0x90
> > [ 46.799752] [<ffffffff8158149c>] ? sysret_check+0x27/0x62
> > [ 46.799760] [<ffffffff81162a09>] sys_ioctl+0x99/0xa0
> > [ 46.799769] [<ffffffff8158146b>] system_call_fastpath+0x16/0x1b
> >
> > Followed by more BUGs and yielding a box that needed in interrupt button pressed to
> > force a reboot.
> >
> > I've previously tested with patches 5 and 6 from Peter Z with good results with threadirqs
> > with boost disabled.
> >
> > Ed
> >
> > > This patch set contains fixes for a trainwreck involving RCU, the
> > > scheduler, and threaded interrupts. This trainwreck involved RCU failing
> > > to properly protect one of its bit fields, use of RCU by the scheduler
> > > from portions of irq_exit() where in_irq() returns false, uses of the
> > > scheduler by RCU colliding with uses of RCU by the scheduler, threaded
> > > interrupts exercising the problematic portions of irq_exit() more heavily,
> > > and so on. The patches are as follows:
> > >
> > > 1. Properly protect current->rcu_read_unlock_special().
> > > Lack of protection was causing RCU to recurse on itself, which
> > > in turn resulted in deadlocks involving RCU and the scheduler.
> > > This affects only RCU_BOOST=y configurations.
> > > 2. Streamline code produced by __rcu_read_unlock(). This one is
> > > an innocent bystander that is being carried due to conflicts
> > > with other patches. (A later version will likely merge it
> > > with #3 below.)
> > > 3. Make __rcu_read_unlock() delay counting the per-task
> > > ->rcu_read_lock_nesting variable to zero until all cleanup for the
> > > just-ended RCU read-side critical section has completed. This
> > > prevents a number of other cases that could result in deadlock
> > > due to self recursion. This affects only TREE_PREEMPT_RCU=y
> > > configurations.
> > > 4. Make scheduler_ipi() correctly identify itself as being
> > > in_irq() when it needs to do anything that might involve RCU,
> > > thus enabling RCU to avoid yet another class of potential
> > > self-recursions and deadlocks. This affects PREEMPT_RCU=y
> > > configurations.
> > > 5. Make irq_exit() inform RCU when it is invoking the scheduler
> > > in situations where in_irq() would return false, thus
> > > allowing RCU to correctly avoid self-recursion. This affects
> > > TREE_PREEMPT_RCU=y configurations.
> > > 6. Make __lock_task_sighand() execute the entire RCU read-side
> > > critical section with irqs disabled. (An experimental patch at
> > > http://marc.info/?l=linux-kernel&m=131110647222185 might possibly
> > > make it legal to have an RCU read-side critical section where
> > > the rcu_read_unlock() is executed with interrupts disabled,
> > > but where some protion of the RCU read-side critical section
> > > was preemptible.) This affects TREE_PREEMPT_RCU=y configurations.
> > >
> > > TINY_PREEMPT_RCU will also need a few of these changes, but in the
> > > meantime this patch stack helps organize things better for testing.
> > > These are also available from the following subject-to-rebase git branch:
> > >
> > > git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-2.6-rcu.git rcu/urgent
> > >
> > > Thanx, Paul
> > >
> > > ------------------------------------------------------------------------
> > >
> > > b/include/linux/sched.h | 3 +++
> > > b/kernel/rcutree_plugin.h | 3 ++-
> > > b/kernel/sched.c | 44 ++++++++++++++++++++++++++++++++++++++------
> > > b/kernel/signal.c | 16 +++++++++++-----
> > > b/kernel/softirq.c | 12 ++++++++++--
> > > kernel/rcutree_plugin.h | 45 ++++++++++++++++++++++++++++++++-------------
> > > 6 files changed, 96 insertions(+), 27 deletions(-)
> > > --
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> > >
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