linux-toradex.git/kernel/rcu, branch v3.17.4

rcu: Use rcu_gp_kthread_wake() to wake up grace period kthreads

2014-11-21T17:23:15+00:00

commit 2aa792e6faf1a00f5accf1f69e87e11a390ba2cd upstream.

The rcu_gp_kthread_wake() function checks for three conditions before
waking up grace period kthreads:

*  Is the thread we are trying to wake up the current thread?
*  Are the gp_flags zero? (all threads wait on non-zero gp_flags condition)
*  Is there no thread created for this flavour, hence nothing to wake up?

If any one of these condition is true, we do not call wake_up().
It was found that there are quite a few avoidable wake ups both during
idle time and under stress induced by rcutorture.

Idle:

Total:66000, unnecessary:66000, case1:61827, case2:66000, case3:0
Total:68000, unnecessary:68000, case1:63696, case2:68000, case3:0

rcutorture:

Total:254000, unnecessary:254000, case1:199913, case2:254000, case3:0
Total:256000, unnecessary:256000, case1:201784, case2:256000, case3:0

Here case{1-3} are the cases listed above. We can avoid these wake
ups by using rcu_gp_kthread_wake() to conditionally wake up the grace
period kthreads.

There is a comment about an implied barrier supplied by the wake_up()
logic.  This barrier is necessary for the awakened thread to see the
updated ->gp_flags.  This flag is always being updated with the root node
lock held. Also, the awakened thread tries to acquire the root node lock
before reading ->gp_flags because of which there is proper ordering.

Hence this commit tries to avoid calling wake_up() whenever we can by
using rcu_gp_kthread_wake() function.

Signed-off-by: Pranith Kumar 
CC: Mathieu Desnoyers 
Signed-off-by: Paul E. McKenney 
Cc: Kamal Mostafa 
Signed-off-by: Greg Kroah-Hartman

rcu: Make nocb leader kthreads process pending callbacks after spawning

2014-08-28T12:59:59+00:00

The nocb callbacks generated before the nocb kthreads are spawned are
enqueued in the nocb queue for later processing. Commit fbce7497ee5af ("rcu:
Parallelize and economize NOCB kthread wakeups") introduced nocb leader kthreads
which checked the nocb_leader_wake flag to see if there were any such pending
callbacks. A case was reported in which newly spawned leader kthreads were not
processing the pending callbacks as this flag was not set, which led to a boot
hang.

The following commit ensures that the newly spawned nocb kthreads process the
pending callbacks by allowing the kthreads to run immediately after spawning
instead of waiting. This is done by inverting the logic of nocb_leader_wake
tests to nocb_leader_sleep which allows us to use the default initialization of
this flag to 0 to let the kthreads run.

Reported-by: Amit Shah 
Signed-off-by: Pranith Kumar 
Link: http://www.spinics.net/lists/kernel/msg1802899.html
[ paulmck: Backported to v3.17-rc2. ]
Signed-off-by: Paul E. McKenney 
Tested-by: Amit Shah

Merge branch 'core-rcu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

2014-08-04T22:55:08+00:00

Pull RCU changes from Ingo Molar:
 "The main changes:

   - torture-test updates
   - callback-offloading changes
   - maintainership changes
   - update RCU documentation
   - miscellaneous fixes"

* 'core-rcu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (32 commits)
  rcu: Allow for NULL tick_nohz_full_mask when nohz_full= missing
  rcu: Fix a sparse warning in rcu_report_unblock_qs_rnp()
  rcu: Fix a sparse warning in rcu_initiate_boost()
  rcu: Fix __rcu_reclaim() to use true/false for bool
  rcu: Remove CONFIG_PROVE_RCU_DELAY
  rcu: Use __this_cpu_read() instead of per_cpu_ptr()
  rcu: Don't use NMIs to dump other CPUs' stacks
  rcu: Bind grace-period kthreads to non-NO_HZ_FULL CPUs
  rcu: Simplify priority boosting by putting rt_mutex in rcu_node
  rcu: Check both root and current rcu_node when setting up future grace period
  rcu: Allow post-unlock reference for rt_mutex
  rcu: Loosen __call_rcu()'s rcu_head alignment constraint
  rcu: Eliminate read-modify-write ACCESS_ONCE() calls
  rcu: Remove redundant ACCESS_ONCE() from tick_do_timer_cpu
  rcu: Make rcu node arrays static const char * const
  signal: Explain local_irq_save() call
  rcu: Handle obsolete references to TINY_PREEMPT_RCU
  rcu: Document deadlock-avoidance information for rcu_read_unlock()
  scripts: Teach get_maintainer.pl about the new "R:" tag
  rcu: Update rcu torture maintainership filename patterns
  ...

Josh has moved

2014-07-31T00:16:13+00:00

My IBM email addresses haven't worked for years; also map some
old-but-functional forwarding addresses to my canonical address.

Update my GPG key fingerprint; I moved to 4096R a long time ago.

Update description.

Signed-off-by: Josh Triplett 
Cc: "Paul E. McKenney" 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

rcu: Allow for NULL tick_nohz_full_mask when nohz_full= missing

2014-07-16T17:44:46+00:00

If there isn't a nohz_full= kernel parameter specified, then
tick_nohz_full_mask can legitimately be NULL.  This can cause
problems when RCU's boot code tries to cpumask_or() this value into
rcu_nocb_mask.  In addition, if NO_HZ_FULL_ALL=y, there is no point
in doing the cpumask_or() in the first place because this will cause
RCU_NOCB_CPU_ALL=y, which in turn will have all bits already set in
rcu_nocb_mask.

This commit therefore avoids the cpumask_or() if NO_HZ_FULL_ALL=y
and checks for !tick_nohz_full_running otherwise, this latter check
catching cases when there was no nohz_full= kernel parameter specified.

Signed-off-by: Paul E. McKenney

Merge branches 'doc.2014.07.08a', 'fixes.2014.07.09a', 'maintainers.2014.07.08b', 'nocbs.2014.07.07a' and 'torture.2014.07.07a' into HEAD

2014-07-09T16:16:54+00:00

doc.2014.07.08a: Documentation updates.
fixes.2014.07.09a: Miscellaneous fixes.
maintainers.2014.07.08b: Maintainership updates.
nocbs.2014.07.07a: Callback-offloading fixes.
torture.2014.07.07a: Torture-test updates.

rcu: Fix a sparse warning in rcu_report_unblock_qs_rnp()

2014-07-09T16:15:51+00:00

This commit annotates rcu_report_unblock_qs_rnp() in order to fix the
following sparse warning:

kernel/rcu/tree_plugin.h:990:13: warning: context imbalance in 'rcu_report_unblock_qs_rnp' - unexpected unlock

Signed-off-by: Pranith Kumar 
Signed-off-by: Paul E. McKenney 
Reviewed-by: Lai Jiangshan

rcu: Fix a sparse warning in rcu_initiate_boost()

2014-07-09T16:15:45+00:00

This commit annotates rcu_initiate_boost() fixes the following sparse
warning:

	kernel/rcu/tree_plugin.h:1494:13: warning: context imbalance in 'rcu_initiate_boost' - unexpected unlock

Signed-off-by: Pranith Kumar 
Signed-off-by: Paul E. McKenney 
Reviewed-by: Lai Jiangshan

rcu: Fix __rcu_reclaim() to use true/false for bool

2014-07-09T16:15:32+00:00

The __rcu_reclaim() function returned 0/1, which is not proper for a
function of type bool.  This commit therefore converts to false/true.

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

rcu: Remove CONFIG_PROVE_RCU_DELAY

2014-07-09T16:15:31+00:00

The CONFIG_PROVE_RCU_DELAY Kconfig parameter doesn't appear to be very
effective at finding race conditions, so this commit removes it.

Signed-off-by: Paul E. McKenney 
Cc: Andi Kleen 
[ paulmck: Remove definition and uses as noted by Paul Bolle. ]