linux-toradex.git/kernel/rcu/srcutree.c, branch v4.17-rc1

Merge branches 'fixes.2018.02.23a', 'srcu.2018.02.20a' and 'torture.2018.02.20a' into HEAD

2018-02-23T23:15:41+00:00

fixes.2018.02.23a: Miscellaneous fixes
srcu.2018.02.20a: SRCU updates
torture.2018.02.20a: Torture-test updates

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: Remove SRCU throttling

2018-02-21T00:21:13+00:00

The code in srcu_gp_end() inserts a delay every 0x3ff grace periods in
order to prevent SRCU grace-period work from consuming an entire CPU
when there is a long sequence of expedited SRCU grace-period requests.
However, all of SRCU's grace-period work is carried out in workqueues,
which are in turn within kthreads, which are automatically throttled as
needed by the scheduler.  In particular, if there is plenty of idle time,
there is no point in throttling.

This commit therefore removes the expedited SRCU grace-period throttling.

Signed-off-by: Paul E. McKenney

srcu: Remove dead code in srcu_gp_end()

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

Of course, compilers will optimize out a dead code. Anyway, remove
any dead code for better readibility.

Signed-off-by: Byungchul Park 
Reviewed-by: Steven Rostedt (VMware) 
Signed-off-by: Paul E. McKenney

srcu: Reduce scans of srcu_data in counter wrap check

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

Currently, given a multi-level srcu_node tree, SRCU can scan the full
set of srcu_data structures at each level when cleaning up after a grace
period.  This, though harmless otherwise, represents pointless overhead.
This commit therefore eliminates this overhead by scanning the srcu_data
structures only when traversing the leaf srcu_node structures.

Signed-off-by: Ildar Ismagilov 
Signed-off-by: Paul E. McKenney

srcu: Prevent sdp->srcu_gp_seq_needed_exp counter wrap

2018-02-21T00:21:11+00:00

SRCU checks each srcu_data structure's grace-period number for counter
wrap four times per cycle by default.  This frequency guarantees that
normal comparisons will detect potential wrap.  However, the expedited
grace-period number is not checked.  The consquences are not too horrible
(a failure to expedite a grace period when requested), but it would be
good to avoid such things.  This commit therefore adds this check to
the expedited grace-period number.

Signed-off-by: Ildar Ismagilov 
Signed-off-by: Paul E. McKenney

srcu: Abstract function name

2018-02-21T00:21:11+00:00

This commit moves to __func__ for function names in the name of better
resilience to change.

Signed-off-by: Paul E. McKenney

rcu: Fix misprint in srcu_funnel_exp_start

2018-02-21T00:12:27+00:00

The srcu_funnel_exp_start() function checks to see if the srcu_struct
structure's expedited grace period counter needs updating to reflect a
newly arrived request for an expedited SRCU grace period.  Unfortunately,
the check is backwards, so this commit reverses the sense of the test.

Signed-off-by: Ildar Ismagilov 
Signed-off-by: Paul E. McKenney

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

srcu: Prohibit call_srcu() use under raw spinlocks

2017-11-28T23:52:33+00:00

Invoking queue_delayed_work() while holding a raw spinlock is forbidden
in -rt kernels, which is exactly what __call_srcu() does, indirectly via
srcu_funnel_gp_start().  This commit therefore downgrades Tree SRCU's
locking from raw to non-raw spinlocks, which works because call_srcu()
is not ever called while holding a raw spinlock.

Reported-by: Sebastian Andrzej Siewior 
Signed-off-by: Paul E. McKenney