Hi Paul and all, > -----Original Message----- > From: [email protected] [mailto:linux-kernel- > [email protected]] On Behalf Of Paul E. McKenney > Sent: Thursday, August 30, 2018 01:21 > To: [email protected] > Cc: [email protected]; [email protected]; [email protected]; > [email protected]; [email protected]; > [email protected]; [email protected]; [email protected]; > [email protected]; [email protected]; [email protected]; > [email protected]; [email protected]; [email protected]; Paul E. > McKenney <[email protected]> > Subject: [PATCH tip/core/rcu 02/19] rcu: Defer reporting RCU-preempt > quiescent states when disabled > > This commit defers reporting of RCU-preempt quiescent states at > rcu_read_unlock_special() time when any of interrupts, softirq, or > preemption are disabled. These deferred quiescent states are reported at a > later RCU_SOFTIRQ, context switch, idle entry, or CPU-hotplug offline > operation. Of course, if another RCU read-side critical section has started > in > the meantime, the reporting of the quiescent state will be further deferred. > > This also means that disabling preemption, interrupts, and/or softirqs will > act > as an RCU-preempt read-side critical section. > This is enforced by checking preempt_count() as needed. > > Some special cases must be handled on an ad-hoc basis, for example, > context switch is a quiescent state even though both the scheduler and > do_exit() disable preemption. In these cases, additional calls to > rcu_preempt_deferred_qs() override the preemption disabling. Similar logic > overrides disabled interrupts in rcu_preempt_check_callbacks() because in > this case the quiescent state happened just before the corresponding > scheduling-clock interrupt. > > In theory, this change lifts a long-standing restriction that required that if > interrupts were disabled across a call to rcu_read_unlock() that the matching > rcu_read_lock() also be contained within that interrupts-disabled region of > code. Because the reporting of the corresponding RCU-preempt quiescent > state is now deferred until after interrupts have been enabled, it is no > longer > possible for this situation to result in deadlocks involving the scheduler's > runqueue and priority-inheritance locks. This may allow some code > simplification that might reduce interrupt latency a bit. Unfortunately, in > practice this would also defer deboosting a low-priority task that had been > subjected to RCU priority boosting, so real-time-response considerations > might well force this restriction to remain in place. > > Because RCU-preempt grace periods are now blocked not only by RCU read- > side critical sections, but also by disabling of interrupts, preemption, and > softirqs, it will be possible to eliminate RCU-bh and RCU-sched in favor of > RCU-preempt in CONFIG_PREEMPT=y kernels. This may require some > additional plumbing to provide the network denial-of-service guarantees > that have been traditionally provided by RCU-bh. Once these are in place, > CONFIG_PREEMPT=n kernels will be able to fold RCU-bh into RCU-sched. > This would mean that all kernels would have but one flavor of RCU, which > would open the door to significant code cleanup. > > Moving to a single flavor of RCU would also have the beneficial effect of > reducing the NOCB kthreads by at least a factor of two. > > Signed-off-by: Paul E. McKenney <[email protected]> [ paulmck: > Apply rcu_read_unlock_special() preempt_count() feedback > from Joel Fernandes. ] > [ paulmck: Adjust rcu_eqs_enter() call to rcu_preempt_deferred_qs() in > response to bug reports from kbuild test robot. ] [ paulmck: Fix bug located > by kbuild test robot involving recursion > via rcu_preempt_deferred_qs(). ] > --- > .../RCU/Design/Requirements/Requirements.html | 50 +++--- > include/linux/rcutiny.h | 5 + > kernel/rcu/tree.c | 9 ++ > kernel/rcu/tree.h | 3 + > kernel/rcu/tree_exp.h | 71 +++++++-- > kernel/rcu/tree_plugin.h | 144 +++++++++++++----- > 6 files changed, 205 insertions(+), 77 deletions(-) >
We started seeing the trace below in our regression system, after I bisected I found this is the offending commit. This appears immediately on boot. Please let me know if you need any additional details. Thanks, Ran [2018-10-27 05:53:07] ================================================================================ [2018-10-27 05:53:07] UBSAN: Undefined behaviour in kernel/rcu/tree_plugin.h:620:28 [2018-10-27 05:53:07] signed integer overflow: [2018-10-27 05:53:07] 0 - -2147483648 cannot be represented in type 'int' [2018-10-27 05:53:07] CPU: 1 PID: 0 Comm: swapper/1 Not tainted 4.19.0-for-upstream-dbg-2018-10-25_03-10-39-82 #1 [2018-10-27 05:53:07] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1ubuntu1 04/01/2014 [2018-10-27 05:53:07] Call Trace: [2018-10-27 05:53:07] dump_stack+0x9a/0xeb [2018-10-27 05:53:07] ubsan_epilogue+0x9/0x7c [2018-10-27 05:53:07] handle_overflow+0x235/0x278 [2018-10-27 05:53:07] ? __ubsan_handle_negate_overflow+0x1bd/0x1bd [2018-10-27 05:53:07] ? sched_clock_local+0xd4/0x140 [2018-10-27 05:53:07] ? kvm_clock_read+0x14/0x30 [2018-10-27 05:53:07] rcu_preempt_deferred_qs+0x12a/0x150 [2018-10-27 05:53:07] rcu_note_context_switch+0x1b9/0x1ac0 [2018-10-27 05:53:07] __schedule+0x22d/0x1fd0 [2018-10-27 05:53:07] ? pci_mmcfg_check_reserved+0x130/0x130 [2018-10-27 05:53:07] ? sched_set_stop_task+0x330/0x330 [2018-10-27 05:53:07] ? lockdep_hardirqs_on+0x360/0x620 [2018-10-27 05:53:07] schedule_idle+0x45/0x80 [2018-10-27 05:53:07] do_idle+0x23e/0x3e0 [2018-10-27 05:53:07] ? check_flags.part.26+0x440/0x440 [2018-10-27 05:53:07] ? arch_cpu_idle_exit+0x40/0x40 [2018-10-27 05:53:07] ? __wake_up_common+0x156/0x5c0 [2018-10-27 05:53:07] ? _raw_spin_unlock_irqrestore+0x59/0x70 [2018-10-27 05:53:07] cpu_startup_entry+0x19/0x20 [2018-10-27 05:53:07] start_secondary+0x420/0x570 [2018-10-27 05:53:07] ? set_cpu_sibling_map+0x2f90/0x2f90 [2018-10-27 05:53:07] secondary_startup_64+0xa4/0xb0 [2018-10-27 05:53:07] ================================================================================ [2018-10-27 05:53:07] ================================================================================ [2018-10-27 05:53:07] UBSAN: Undefined behaviour in kernel/rcu/tree_plugin.h:624:28 [2018-10-27 05:53:07] signed integer overflow: [2018-10-27 05:53:07] -2147483648 + -2147483648 cannot be represented in type 'int' [2018-10-27 05:53:07] CPU: 1 PID: 0 Comm: swapper/1 Not tainted 4.19.0-for-upstream-dbg-2018-10-25_03-10-39-82 #1 [2018-10-27 05:53:07] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1ubuntu1 04/01/2014 [2018-10-27 05:53:07] Call Trace: [2018-10-27 05:53:07] dump_stack+0x9a/0xeb [2018-10-27 05:53:07] ubsan_epilogue+0x9/0x7c [2018-10-27 05:53:07] handle_overflow+0x235/0x278 [2018-10-27 05:53:07] ? __ubsan_handle_negate_overflow+0x1bd/0x1bd [2018-10-27 05:53:07] ? check_flags.part.26+0x440/0x440 [2018-10-27 05:53:07] ? _raw_spin_unlock_irqrestore+0x3c/0x70 [2018-10-27 05:53:07] ? _raw_spin_unlock_irqrestore+0x3c/0x70 [2018-10-27 05:53:07] ? lockdep_hardirqs_off+0x1fd/0x2c0 [2018-10-27 05:53:07] ? kvm_clock_read+0x14/0x30 [2018-10-27 05:53:07] rcu_preempt_deferred_qs+0x145/0x150 [2018-10-27 05:53:07] rcu_note_context_switch+0x1b9/0x1ac0 [2018-10-27 05:53:07] __schedule+0x22d/0x1fd0 [2018-10-27 05:53:07] ? pci_mmcfg_check_reserved+0x130/0x130 [2018-10-27 05:53:07] ? sched_set_stop_task+0x330/0x330 [2018-10-27 05:53:07] ? lockdep_hardirqs_on+0x360/0x620 [2018-10-27 05:53:07] schedule_idle+0x45/0x80 [2018-10-27 05:53:07] do_idle+0x23e/0x3e0 [2018-10-27 05:53:07] ? check_flags.part.26+0x440/0x440 [2018-10-27 05:53:07] ? arch_cpu_idle_exit+0x40/0x40 [2018-10-27 05:53:07] ? __wake_up_common+0x156/0x5c0 [2018-10-27 05:53:07] ? _raw_spin_unlock_irqrestore+0x59/0x70 [2018-10-27 05:53:07] cpu_startup_entry+0x19/0x20 [2018-10-27 05:53:07] start_secondary+0x420/0x570 [2018-10-27 05:53:07] ? set_cpu_sibling_map+0x2f90/0x2f90 [2018-10-27 05:53:07] secondary_startup_64+0xa4/0xb0 [2018-10-27 05:53:07] ================================================================================
