linux-stable.git/kernel/rcu, branch v4.17

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

torture: Provide more sensible nreader/nwriter defaults for rcuperf

2018-02-21T00:22:01+00:00

The default values for nreader and nwriter are apparently not all that
user-friendly, resulting in people doing scalability tests that ran all
runs at large scale.  This commit therefore makes both the nreaders and
nwriters module default to the number of CPUs, and adds a comment to
rcuperf.c stating that the number of CPUs should be specified using the
nr_cpus kernel boot parameter.  This commit also eliminates the redundant
rcuperf scripting specification of default values for these parameters.

Signed-off-by: Paul E. McKenney

rcutorture: Record which grace-period primitives are tested

2018-02-21T00:21:58+00:00

The rcu_torture_writer() function adapts to requested testing from module
parameters as well as the function pointers in the structure referenced
by cur_ops.  However, as long as the module parameters do not conflict
with the function pointers, this adaptation is silent.  This silence can
result in confusion as to exactly what was tested, which could in turn
result in untested RCU code making its way into mainline.

This commit therefore makes rcu_torture_writer() announce exactly which
portions of RCU's API it ends up testing.

Signed-off-by: Paul E. McKenney

rcutorture: Re-enable testing of dynamic expediting

2018-02-21T00:21:57+00:00

During boot, normal grace periods are processed as expedited.  When
rcutorture is built into the kernel, it starts during boot and thus
detects that normal grace periods are unconditionally expedited.
Therefore, rcutorture concludes that there is no point in trying
to dynamically enable expediting, do it disables this aspect of testing,
which is a bit of an overreaction to the temporary boot-time expediting.

This commit therefore rechecks forced expediting throughout the test,
enabling dynamic expediting if normal grace periods are processed
normally at any point.

Signed-off-by: Paul E. McKenney

rcutorture: Avoid fake-writer use of undefined primitives

2018-02-21T00:21:56+00:00

Currently the rcu_torture_fakewriter() function invokes cur_ops->sync()
and cur_ops->exp_sync() without first checking to see if they are in
fact non-NULL.  This results in kernel NULL pointer dereferences when
testing RCU implementations that choose not to provide the full set of
primitives.  Given that it is perfectly reasonable to have specialized
RCU implementations that provide only a subset of the RCU API, this is
a bug in rcutorture.

This commit therefore makes rcu_torture_fakewriter() check function
pointers before invoking them, thus allowing it to test subsetted
RCU implementations.

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

rcutorture: Abstract function and module names

2018-02-21T00:21:56+00:00

This commit moves to __func__ for function names and for KBUILD_MODNAME
for module names, all in the name of better resilience to change.

Signed-off-by: Paul E. McKenney

rcutorture: Replace multi-instance kzalloc() with kcalloc()

2018-02-21T00:21:55+00:00

This commit replaces array-allocation calls to kzalloc() with
equivalent calls to kcalloc().

Signed-off-by: Paul E. McKenney

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