On Thu, Apr 05, 2012 at 02:47:49PM -0700, Paul E. McKenney wrote: > On Fri, Apr 06, 2012 at 12:30:06AM +0300, Sergey Senozhatsky wrote: > > On (04/03/12 07:58), Paul E. McKenney wrote: > > > On Tue, Apr 03, 2012 at 02:10:43AM +0300, Sergey Senozhatsky wrote: > > > > On (04/02/12 06:09), Paul E. McKenney wrote: > > > > > On Mon, Apr 02, 2012 at 10:09:11AM +0300, Sergey Senozhatsky wrote: > > > > > > Hello, > > > > > > > > > > > > commit e5601400081651060a59bd1f45f2821bb8e97f95 > > > > > > Author: Paul E. McKenney <paul.mckenney@xxxxxxxxxx> > > > > > > Date: Sat Jan 7 11:03:57 2012 -0800 > > > > > > > > > > > > rcu: Simplify offline processing > > > > > > > > > > > > Move ->qsmaskinit and blkd_tasks[] manipulation to the CPU_DYING > > > > > > notifier. This simplifies the code by eliminating a potential > > > > > > deadlock and by reducing the responsibilities of force_quiescent_state(). > > > > > > Also rename functions to make their connection to the CPU-hotplug > > > > > > stages explicit. > > > > > > > > > > > > Signed-off-by: Paul E. McKenney <paul.mckenney@xxxxxxxxxx> > > > > > > Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> > > > > > > > > > > > > > > > > > > introduced WARN_ON_ONCE(cpu_is_offline(smp_processor_id())); to __call_rcu() > > > > > > function, Paul also added cpu_offline checks to other routines (e.g. callbacks) > > > > > > in later commits. It happens that kmemleak() triggers one of them. > > > > > > > > > > > > During cpu core offline, kfree()->kmemleak_free()->put_object()-->__call_rcu() chain > > > > > > for struct intel_shared_regs * is executed when no struct users left on this core -- > > > > > > all CPUs are dead or dying. > > > > > > > > > > > > > > > > > > [ 4703.342462] CPU 3 is now offline > > > > > > [ 4705.588116] ------------[ cut here ]------------ > > > > > > [ 4705.588129] WARNING: at kernel/rcutree.c:1823 __call_rcu+0x9d/0x1d2() > > > > > > [..] > > > > > > [ 4705.588196] Call Trace: > > > > > > [ 4705.588207] [<ffffffff81059a00>] ? synchronize_srcu+0x6/0x17 > > > > > > [ 4705.588215] [<ffffffff8103364e>] warn_slowpath_common+0x83/0x9c > > > > > > [ 4705.588223] [<ffffffff8111e627>] ? get_object+0x31/0x31 > > > > > > [ 4705.588229] [<ffffffff81033681>] warn_slowpath_null+0x1a/0x1c > > > > > > [ 4705.588235] [<ffffffff810af770>] __call_rcu+0x9d/0x1d2 > > > > > > [ 4705.588243] [<ffffffff81013f52>] ? intel_pmu_cpu_dying+0x3b/0x5d > > > > > > [ 4705.588249] [<ffffffff810af8f1>] call_rcu_sched+0x17/0x19 > > > > > > [ 4705.588255] [<ffffffff8111eb7e>] put_object+0x47/0x4b > > > > > > [ 4705.588261] [<ffffffff8111ed8b>] delete_object_full+0x2a/0x2e > > > > > > [ 4705.588269] [<ffffffff81491dc8>] kmemleak_free+0x26/0x45 > > > > > > [ 4705.588274] [<ffffffff8111691f>] kfree+0x130/0x221 > > > > > > [ 4705.588280] [<ffffffff81013f52>] intel_pmu_cpu_dying+0x3b/0x5d > > > > > > [ 4705.588287] [<ffffffff8149cb83>] x86_pmu_notifier+0xaf/0xb9 > > > > > > [ 4705.588296] [<ffffffff814b0e9d>] notifier_call_chain+0xac/0xd9 > > > > > > [ 4705.588303] [<ffffffff81059c9e>] __raw_notifier_call_chain+0xe/0x10 > > > > > > [ 4705.588309] [<ffffffff810354ec>] __cpu_notify+0x20/0x37 > > > > > > [ 4705.588314] [<ffffffff81035516>] cpu_notify+0x13/0x15 > > > > > > [ 4705.588320] [<ffffffff81490fab>] take_cpu_down+0x28/0x2e > > > > > > [ 4705.588326] [<ffffffff8109ef7f>] stop_machine_cpu_stop+0x96/0xf1 > > > > > > [ 4705.588332] [<ffffffff8109ece3>] cpu_stopper_thread+0xe3/0x183 > > > > > > [ 4705.588338] [<ffffffff8109eee9>] ? queue_stop_cpus_work+0xd0/0xd0 > > > > > > [ 4705.588344] [<ffffffff814ad382>] ? _raw_spin_unlock_irqrestore+0x47/0x65 > > > > > > [ 4705.588353] [<ffffffff81087d0d>] ? trace_hardirqs_on_caller+0x119/0x175 > > > > > > [ 4705.588358] [<ffffffff81087d76>] ? trace_hardirqs_on+0xd/0xf > > > > > > [ 4705.588364] [<ffffffff8109ec00>] ? cpu_stop_signal_done+0x2c/0x2c > > > > > > [ 4705.588370] [<ffffffff810544a9>] kthread+0x8b/0x93 > > > > > > [ 4705.588378] [<ffffffff814b5f34>] kernel_thread_helper+0x4/0x10 > > > > > > [ 4705.588385] [<ffffffff814ad7f0>] ? retint_restore_args+0x13/0x13 > > > > > > [ 4705.588391] [<ffffffff8105441e>] ? __init_kthread_worker+0x5a/0x5a > > > > > > [ 4705.588397] [<ffffffff814b5f30>] ? gs_change+0x13/0x13 > > > > > > [ 4705.588400] ---[ end trace 720328982e35a713 ]--- > > > > > > [ 4705.588507] CPU 2 is now offline > > > > > > > > > > > > > > > > > > My first solution was to return from delete_object() if object deallocation > > > > > > performed on cpu_is_offline(smp_processor_id()), marking object with special > > > > > > flag, say OBJECT_ORPHAN. And issue real object_delete() during scan (for example) > > > > > > when we see OBJECT_ORPHAN object. > > > > > > That, however, requires to handle special case when cpu core offlined > > > > > > for small period of time, leading to object insertion error in > > > > > > create_object(), which either may be handled in 2 possible ways (assuming > > > > > > that lookup_object() returned OBJECT_ORPHAN): > > > > > > #1 delete orphaned object and retry with insertion (*) > > > > > > #2 re-set existing orphan object > > > > > > > > > > > > > > > > > > (*) performing delete_object() from within create_object() requires releasing > > > > > > of held kmemleak and object locks, which is racy with other create_object() and > > > > > > any possible scan() activities. > > > > > > > > > > > > Yet I'm not exactly sure that option #2 is the correct one. > > > > > > (I've kind of a patch [not properly tested, etc.] for #2 option). > > > > > > > > > > Alternatively, I can make RCU tolerate __call_rcu() from late in the > > > > > CPU_DYING notifiers without too much trouble. > > > > > > > > > > > > > Well, if that will `do the trick', then I'm ready to test it. > > > > > > If you are feeling lucky, please try out the attached untested patch. > > > I will repost in the rather likely event that my testing finds bugs. > > > > > > Thanx, Paul > > > > > > > Hello Paul, > > I'm running the kernel with your patch for a couple of days already and > > so far, so good. > > No problems here as well. Thank you for testing this -- I will add > your Tested-by. OK... To qualify for 3.4, this needs to be a pure regression fix. The WARN_ON() is a regression, but leaving callbacks posted by CPU_DYING callbacks has been around for some time. So I need to post only the removal of the WARN_ON(), please see below. Thanx, Paul ------------------------------------------------------------------------ rcu: Permit call_rcu() from CPU_DYING notifiers As of commit 29494be7, RCU adopts callbacks from the dying CPU in its CPU_DYING notifier, which means that any callbacks posted by later CPU_DYING notifiers are ignored until the CPU comes back online. A WARN_ON_ONCE() was added to __call_rcu() by commit e5601400 to check for this condition. Although this condition did not trigger (at least as far I as know) during -next testing, it did recently trigger in mainline (https://lkml.org/lkml/2012/4/2/34). What is needed longer term is for RCU's CPU_DEAD notifier to adopt any callbacks that were posted by CPU_DYING notifiers, however, the Linux kernel has been running with this sort of thing happening for quite some time. So the only thing that qualifies as a regression is the WARN_ON_ONCE(), which this commit removes. Making RCU's CPU_DEAD notifier adopt callbacks posted by CPU_DYING notifiers is a topic for the 3.5 release of the Linux kernel. Reported-by: Sergey Senozhatsky <sergey.senozhatsky@xxxxxxxxx> Signed-off-by: Paul E. McKenney <paul.mckenney@xxxxxxxxxx> Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> diff --git a/kernel/rcutree.c b/kernel/rcutree.c index 1050d6d..d0c5baf 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -1820,7 +1820,6 @@ __call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu), * a quiescent state betweentimes. */ local_irq_save(flags); - WARN_ON_ONCE(cpu_is_offline(smp_processor_id())); rdp = this_cpu_ptr(rsp->rda); /* Add the callback to our list. */ -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>