linux-stable.git/kernel/rcu/tree.c, branch v4.17.2

rcu: Create RCU-specific workqueues with rescuers

2018-02-23T23:14:40+00:00

RCU's expedited grace periods can participate in out-of-memory deadlocks
due to all available system_wq kthreads being blocked and there not being
memory available to create more.  This commit prevents such deadlocks
by allocating an RCU-specific workqueue_struct at early boot time, and
providing it with a rescuer to ensure forward progress.  This uses the
shiny new init_rescuer() function provided by Tejun (but indirectly).

This commit also causes SRCU to use this new RCU-specific
workqueue_struct.  Note that SRCU's use of workqueues never blocks them
waiting for readers, so this should be safe from a forward-progress
viewpoint.  Note that this moves SRCU from system_power_efficient_wq
to a normal workqueue.  In the unlikely event that this results in
measurable degradation, a separate power-efficient workqueue will be
creates for SRCU.

Reported-by: Prateek Sood 
Reported-by: Tejun Heo 
Signed-off-by: Paul E. McKenney 
Acked-by: Tejun Heo

rcu: Use wrapper for lockdep asserts

2018-02-21T00:12:26+00:00

Commits c0b334c5bfa9 and ea9b0c8a26a2 introduced new sparse warnings
by accessing rcu_node->lock directly and ignoring the __private
marker.  Introduce a new wrapper and use it.  Also fix a similar problem
in srcutree.c introduced by a3883df3935e.

Signed-off-by: Matthew Wilcox 
Signed-off-by: Paul E. McKenney

rcu: More clearly identify grace-period kthread stack dump

2018-02-21T00:10:29+00:00

It is not always obvious that the stack dump from a starved grace-period
kthread isn't instead that of a CPU stalling the current grace period.
This commit therefore adds a pr_err() flagging these dumps.

Reported-by: Peter Zijlstra 
Signed-off-by: Paul E. McKenney

rcu: Remove obsolete force-quiescent-state statistics for debugfs

2018-02-21T00:10:29+00:00

The debugfs interface displayed statistics on RCU-pending checks but
this interface has since been removed.  This commit therefore removes the
no-longer-used rcu_state structure's ->n_force_qs_lh and ->n_force_qs_ngp
fields along with their updates.  (Though the ->n_force_qs_ngp field
was actually not used at all, embarrassingly enough.)

If this information proves necessary in the future, the corresponding
event traces will be added.

Signed-off-by: Paul E. McKenney

rcu: Remove obsolete __rcu_pending() statistics for debugfs

2018-02-21T00:10:28+00:00

The debugfs interface displayed statistics on RCU-pending checks
but this interface has since been removed.  This commit therefore
removes the no-longer-used rcu_data structure's ->n_rcu_pending,
->n_rp_core_needs_qs, ->n_rp_report_qs, ->n_rp_cb_ready,
->n_rp_cpu_needs_gp, ->n_rp_gp_completed, ->n_rp_gp_started,
->n_rp_nocb_defer_wakeup, and ->n_rp_need_nothing fields along with
their updates.

If this information proves necessary in the future, the corresponding
event traces will be added.

Signed-off-by: Paul E. McKenney

rcu: Remove obsolete callback-invocation statistics for debugfs

2018-02-21T00:10:27+00:00

The debugfs interface displayed statistics on RCU callback invocation but
this interface has since been removed.  This commit therefore removes the
no-longer-used rcu_data structure's ->n_cbs_invoked and ->n_nocbs_invoked
fields along with their updates.

If this information proves necessary in the future, the corresponding
event traces will be added.

Signed-off-by: Paul E. McKenney

rcu: Remove unnecessary spinlock in rcu_boot_init_percpu_data()

2018-02-15T23:40:36+00:00

Since rcu_boot_init_percpu_data() is only called at boot time,
there is no data race and spinlock is not needed.

Signed-off-by: Lihao Liang 
Signed-off-by: Paul E. McKenney

Merge branches 'cond_resched.2017.12.04a', 'dyntick.2017.11.28a', 'fixes.2017.12.11a', 'srbd.2017.12.05a' and 'torture.2017.12.11a' into HEAD

2017-12-11T17:21:58+00:00

cond_resched.2017.12.04a: Convert cond_resched_rcu_qs() to cond_resched()
dyntick.2017.11.28a: Make RCU dynticks handle interrupts from NMI
fixes.2017.12.11a: Miscellaneous fixes
srbd.2017.12.05a: Remove now-redundant smp_read_barrier_depends()
torture.2017.12.11a: Torture-testing update

rcu: Add comment giving debug strategy for double call_rcu()

2017-12-11T17:17:39+00:00

The following statement has for some reason proven non-intuitive:

	WARN_ON_ONCE(rcu_segcblist_empty(&rdp->cblist) != (count == 0));

This commit therefore adds a comment that states that this warning
usually triggers in response to a double call_rcu(), which is sort
of like a double free.  The comment also suggests building with
CONFIG_DEBUG_OBJECTS_RCU_HEAD=y to track down the double call_rcu().

Reported-by: David Howells 
Signed-off-by: Paul E. McKenney

rcu: Simplify rcu_eqs_{enter,exit}() non-idle task debug code

2017-11-28T23:51:21+00:00

The code that checks for non-idle non-nohz_idle-usermode tasks invoking
rcu_eqs_enter() and rcu_eqs_exit() prints a considerable quantity of
helpful information.  However, these checks fire rarely, so the extra
complexity is no longer worth it.  This commit therefore replaces this
debug code with simple WARN_ON_ONCE() statements.

Signed-off-by: Paul E. McKenney