linux-toradex.git/kernel/rcutorture.c, branch v3.6

rcu: Fix broken strings in RCU's source code.

2012-07-06T13:01:49+00:00

Although the C language allows you to break strings across lines, doing
this makes it hard for people to find the Linux kernel code corresponding
to a given console message.  This commit therefore fixes broken strings
throughout RCU's source code.

Suggested-by: Josh Triplett 
Suggested-by: Ingo Molnar 
Signed-off-by: Paul E. McKenney

rcu: Fix code-style issues involving "else"

2012-07-06T13:01:48+00:00

The Linux kernel coding style says that single-statement blocks should
omit curly braces unless the other leg of the "if" statement has
multiple statements, in which case the curly braces should be included.
This commit fixes RCU's violations of this rule.

Signed-off-by: Paul E. McKenney 
Signed-off-by: Paul E. McKenney 
Reviewed-by: Josh Triplett

rcu: Make rcutorture fakewriters invoke rcu_barrier()

2012-07-02T19:34:04+00:00

The current rcutorture rcu_barrier() testing never intentionally runs
more than one instance of rcu_barrier() at a given time.  This fails
to test the the shiny new concurrency features of rcu_barrier().  This
commit therefore modifies the rcutorture fakewriter kthread to randomly
invoke rcu_barrier() rather than the usual synchronize_rcu().

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

rcu: Fix diagnostic-printk typo in rcutorture

2012-07-02T19:34:03+00:00

The rcu_torture_barrier() function has a copy-and-paste typo in the
string passed to rcutorture_shutdown_absorb(), which this commit fixes.

Signed-off-by: Paul E. McKenney 
Signed-off-by: Paul E. McKenney 
Reviewed-by: Josh Triplett

rcu: Fix bug in rcu_barrier() torture test

2012-07-02T19:34:03+00:00

The child threads in the rcu_torture_barrier_cbs() are improperly
synchronized, which can cause the rcu_barrier() tests to hang.  The
failure mode is as follows:

1.	CPU 0 running in rcu_torture_barrier() sets barrier_cbs_count
    	to n_barrier_cbs.

2.	CPU 1 running in rcu_torture_barrier_cbs() wakes up, posts
    	its RCU callback, and atomically decrements barrier_cbs_count.
    	Because barrier_cbs_count is not zero, it does not do the wake_up().

3.	CPU 2 running in rcu_torture_barrier_cbs() wakes up, but
    	finds that barrier_cbs_count is not equal to n_barrier_cbs,
    	and so returns to sleep.

4.	The value of barrier_cbs_count therefore never reaches zero,
    	which causes the test to hang.

This commit therefore uses a phase variable to coordinate the test,
preventing this scenario from occurring.

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

rcu: Test srcu_barrier() from rcutorture test suite

2012-07-02T19:34:03+00:00

SRCU now has a call_srcu() and an srcu_barrier(), but rcutorture does not
test them.  This commit adds the machinery to allow rcutorture's existing
tests for call_rcu() and rcu_barrier() to apply to the SRCU equivalents.

Signed-off-by: Paul E. McKenney 
Reviewed-by: Josh Triplett

rcu: Rationalize ordering of torture_ops list

2012-07-02T19:34:03+00:00

Move the raw SRCU interfaces out of the middle of the normal SRCU
interfaces.

Signed-off-by: Paul E. McKenney 
Reviewed-by: Josh Triplett

rcu: Add rcutorture test for call_srcu()

2012-04-30T17:48:26+00:00

Add srcu_torture_deferred_free() for srcu_ops so as to test the new
call_srcu().  Rename the original srcu_ops to srcu_sync_ops.

Signed-off-by: Lai Jiangshan 
Signed-off-by: Paul E. McKenney

rcu: Direct algorithmic SRCU implementation

2012-04-30T17:48:19+00:00

The current implementation of synchronize_srcu_expedited() can cause
severe OS jitter due to its use of synchronize_sched(), which in turn
invokes try_stop_cpus(), which causes each CPU to be sent an IPI.
This can result in severe performance degradation for real-time workloads
and especially for short-interation-length HPC workloads.  Furthermore,
because only one instance of try_stop_cpus() can be making forward progress
at a given time, only one instance of synchronize_srcu_expedited() can
make forward progress at a time, even if they are all operating on
distinct srcu_struct structures.

This commit, inspired by an earlier implementation by Peter Zijlstra
(https://lkml.org/lkml/2012/1/31/211) and by further offline discussions,
takes a strictly algorithmic bits-in-memory approach.  This has the
disadvantage of requiring one explicit memory-barrier instruction in
each of srcu_read_lock() and srcu_read_unlock(), but on the other hand
completely dispenses with OS jitter and furthermore allows SRCU to be
used freely by CPUs that RCU believes to be idle or offline.

The update-side implementation handles the single read-side memory
barrier by rechecking the per-CPU counters after summing them and
by running through the update-side state machine twice.

This implementation has passed moderate rcutorture testing on both
x86 and Power.  Also updated to use this_cpu_ptr() instead of per_cpu_ptr(),
as suggested by Peter Zijlstra.

Reported-by: Peter Zijlstra 
Signed-off-by: Paul E. McKenney 
Signed-off-by: Paul E. McKenney 
Acked-by: Peter Zijlstra 
Reviewed-by: Lai Jiangshan

rcu: Introduce rcutorture testing for rcu_barrier()

2012-04-30T17:48:18+00:00

Although rcutorture does invoke rcu_barrier() and friends, it cannot
really be called a torture test given that it invokes them only once
at the end of the test.  This commit therefore introduces heavy-duty
rcutorture testing for rcu_barrier(), which may be carried out
concurrently with normal rcutorture testing.

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