user/sven/linux.git/kernel/rcu/tree.c, branch v4.4.153

rcu: Allow for page faults in NMI handlers

2017-10-18T07:20:41Z

commit 28585a832602747cbfa88ad8934013177a3aae38 upstream. A number of architecture invoke rcu_irq_enter() on exception entry in order to allow RCU read-side critical sections in the exception handler when the exception is from an idle or nohz_full CPU. This works, at least unless the exception happens in an NMI handler. In that case, rcu_nmi_enter() would already have exited the extended quiescent state, which would mean that rcu_irq_enter() would (incorrectly) cause RCU to think that it is again in an extended quiescent state. This will in turn result in lockdep splats in response to later RCU read-side critical sections. This commit therefore causes rcu_irq_enter() and rcu_irq_exit() to take no action if there is an rcu_nmi_enter() in effect, thus avoiding the unscheduled return to RCU quiescent state. This in turn should make the kernel safe for on-demand RCU voyeurism. Link: http://lkml.kernel.org/r/20170922211022.GA18084@linux.vnet.ibm.com Cc: stable@vger.kernel.org Fixes: 0be964be0 ("module: Sanitize RCU usage and locking") Reported-by: Steven Rostedt Signed-off-by: Paul E. McKenney Signed-off-by: Steven Rostedt (VMware) Signed-off-by: Greg Kroah-Hartman

Merge branches 'fixes.2015.10.06a' and 'exp.2015.10.07a' into HEAD

2015-10-07T23:05:21Z

exp.2015.10.07a: Reduce OS jitter of RCU-sched expedited grace periods. fixes.2015.10.06a: Miscellaneous fixes.

rcu: Better hotplug handling for synchronize_sched_expedited()

2015-10-07T23:02:50Z

Earlier versions of synchronize_sched_expedited() can prematurely end grace periods due to the fact that a CPU marked as cpu_is_offline() can still be using RCU read-side critical sections during the time that CPU makes its last pass through the scheduler and into the idle loop and during the time that a given CPU is in the process of coming online. This commit therefore eliminates this window by adding additional interaction with the CPU-hotplug operations. Signed-off-by: Paul E. McKenney

rcu: Add tasks to expedited stall-warning messages

2015-10-07T23:02:50Z

This commit adds task-print ability to the expedited RCU CPU stall warning messages in preparation for adding stall warnings to synchornize_rcu_expedited(). Signed-off-by: Paul E. McKenney

rcu: Add online/offline info to expedited stall warning message

2015-10-07T23:02:50Z

This commit makes the RCU CPU stall warning message print online/offline indications immediately after the CPU number. A "O" indicates global offline, a "." global online, and a "o" indicates RCU believes that the CPU is offline for the current grace period and "." otherwise, and an "N" indicates that RCU believes that the CPU will be offline for the next grace period, and "." otherwise, all right after the CPU number. So for CPU 10, you would normally see "10-...:" indicating that everything believes that the CPU is online. Signed-off-by: Paul E. McKenney

rcu: Consolidate expedited CPU selection

2015-10-07T23:02:50Z

Now that sync_sched_exp_select_cpus() and sync_rcu_exp_select_cpus() are identical aside from the the argument to smp_call_function_single(), this commit consolidates them with a functional argument. Signed-off-by: Paul E. McKenney

rcu: Prepare for consolidating expedited CPU selection

2015-10-07T23:02:50Z

This commit brings sync_sched_exp_select_cpus() into alignment with sync_rcu_exp_select_cpus(), as a first step towards consolidating them into one function. Signed-off-by: Paul E. McKenney

rcu: Stop excluding CPU hotplug in synchronize_sched_expedited()

2015-10-07T23:02:49Z

Now that synchronize_sched_expedited() uses IPIs, a hook in rcu_sched_qs(), and the ->expmask field in the rcu_node combining tree, it is no longer necessary to exclude CPU hotplug. Any races with CPU hotplug will be detected when attempting to send the IPI. This commit therefore removes the code excluding CPU hotplug operations. Signed-off-by: Paul E. McKenney

rcu: Stop silencing lockdep false positive for expedited grace periods

2015-10-07T23:02:49Z

This reverts commit af859beaaba4 (rcu: Silence lockdep false positive for expedited grace periods). Because synchronize_rcu_expedited() no longer invokes synchronize_sched_expedited(), ->exp_funnel_mutex acquisition is no longer nested, so the false positive no longer happens. This commit therefore removes the extra lockdep data structures, as they are no longer needed.

rcu: Switch synchronize_sched_expedited() to IPI

2015-10-07T23:01:12Z

This commit switches synchronize_sched_expedited() from stop_one_cpu_nowait() to smp_call_function_single(), thus moving from an IPI and a pair of context switches to an IPI and a single pass through the scheduler. Of course, if the scheduler actually does decide to switch to a different task, there will still be a pair of context switches, but there would likely have been a pair of context switches anyway, just a bit later. Signed-off-by: Paul E. McKenney