linux-stable.git/include/linux/rcupdate.h, branch v4.19.26 Linux kernel stable tree rcu: Improve RCU-tasks naming and comments 2018-07-12T22:39:15+00:00 Paul E. McKenney paulmck@linux.vnet.ibm.com 2018-05-14T20:52:27+00:00 6f56f714db067056c80f5d71510118f82872e34c The naming and comments associated with some RCU-tasks code make the faulty assumption that context switches due to cond_resched() are voluntary. As several people pointed out, this is not the case. This commit therefore updates function names and comments to better reflect current reality. Reported-by: Byungchul Park <byungchul.park@lge.com> Reported-by: Joel Fernandes <joel@joelfernandes.org> Reported-by: Steven Rostedt <rostedt@goodmis.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> 
The naming and comments associated with some RCU-tasks code make
the faulty assumption that context switches due to cond_resched()
are voluntary.  As several people pointed out, this is not the case.
This commit therefore updates function names and comments to better
reflect current reality.

Reported-by: Byungchul Park <byungchul.park@lge.com>
Reported-by: Joel Fernandes <joel@joelfernandes.org>
Reported-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
rcu: rcupdate.h: Get rid of Sphinx warnings at rcu_pointer_handoff() 2018-07-12T22:39:12+00:00 Mauro Carvalho Chehab mchehab+samsung@kernel.org 2018-05-07T09:35:46+00:00 1445e9175bead409bb9930f3c745246a09f22cf6 The code example at rcupdate.h currently produce lots of warnings: ./include/linux/rcupdate.h:572: WARNING: Unexpected indentation. ./include/linux/rcupdate.h:576: WARNING: Unexpected indentation. ./include/linux/rcupdate.h:580: WARNING: Block quote ends without a blank line; unexpected unindent. ./include/linux/rcupdate.h:582: WARNING: Block quote ends without a blank line; unexpected unindent. ./include/linux/rcupdate.h:582: WARNING: Inline literal start-string without end-string. This commit therefore changes it to a code-block. Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> 
The code example at rcupdate.h currently produce lots of warnings:

	./include/linux/rcupdate.h:572: WARNING: Unexpected indentation.
	./include/linux/rcupdate.h:576: WARNING: Unexpected indentation.
	./include/linux/rcupdate.h:580: WARNING: Block quote ends without a blank line; unexpected unindent.
	./include/linux/rcupdate.h:582: WARNING: Block quote ends without a blank line; unexpected unindent.
	./include/linux/rcupdate.h:582: WARNING: Inline literal start-string without end-string.

This commit therefore changes it to a code-block.

Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
rcu: Improve rcu_note_voluntary_context_switch() reporting 2018-07-12T22:39:12+00:00 Byungchul Park byungchul.park@lge.com 2018-05-11T08:30:34+00:00 07f27570dcd148a5f4de7dc3513c1d1cd069b362 We expect a quiescent state of TASKS_RCU when cond_resched_tasks_rcu_qs() is called, no matter whether it actually be scheduled or not. However, it currently doesn't report the quiescent state when the task enters into __schedule() as it's called with preempt = true. So make it report the quiescent state unconditionally when cond_resched_tasks_rcu_qs() is called. And in TINY_RCU, even though the quiescent state of rcu_bh also should be reported when the tick interrupt comes from user, it doesn't. So make it reported. Lastly in TREE_RCU, rcu_note_voluntary_context_switch() should be reported when the tick interrupt comes from not only user but also idle, as an extended quiescent state. Signed-off-by: Byungchul Park <byungchul.park@lge.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> [ paulmck: Simplify rcutiny portion given no RCU-tasks for !PREEMPT. ] 
We expect a quiescent state of TASKS_RCU when cond_resched_tasks_rcu_qs()
is called, no matter whether it actually be scheduled or not. However,
it currently doesn't report the quiescent state when the task enters
into __schedule() as it's called with preempt = true. So make it report
the quiescent state unconditionally when cond_resched_tasks_rcu_qs() is
called.

And in TINY_RCU, even though the quiescent state of rcu_bh also should
be reported when the tick interrupt comes from user, it doesn't. So make
it reported.

Lastly in TREE_RCU, rcu_note_voluntary_context_switch() should be
reported when the tick interrupt comes from not only user but also idle,
as an extended quiescent state.

Signed-off-by: Byungchul Park <byungchul.park@lge.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
[ paulmck: Simplify rcutiny portion given no RCU-tasks for !PREEMPT. ]
rcu: Make rcu_read_unlock_special() static 2018-07-12T22:39:11+00:00 Paul E. McKenney paulmck@linux.vnet.ibm.com 2018-05-08T22:29:10+00:00 3949fa9bac090ad217534c30bc3b6572289abf21 Because rcu_read_unlock_special() is no longer used outside of kernel/rcu/tree_plugin.h, this commit makes it static. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> 
Because rcu_read_unlock_special() is no longer used outside of
kernel/rcu/tree_plugin.h, this commit makes it static.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
rcu: Update documentation of rcu_read_unlock() 2018-06-10T04:14:01+00:00 Anna-Maria Gleixner anna-maria@linutronix.de 2018-05-25T09:05:06+00:00 ec84b27f9b3b569f9235413d1945a2006b97b0aa Since commit b4abf91047cf ("rtmutex: Make wait_lock irq safe") the explanation in rcu_read_unlock() documentation about irq unsafe rtmutex wait_lock is no longer valid. Remove it to prevent kernel developers reading the documentation to rely on it. Suggested-by: Eric W. Biederman <ebiederm@xmission.com> Signed-off-by: Anna-Maria Gleixner <anna-maria@linutronix.de> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Reviewed-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Acked-by: "Eric W. Biederman" <ebiederm@xmission.com> Cc: bigeasy@linutronix.de Link: https://lkml.kernel.org/r/20180525090507.22248-2-anna-maria@linutronix.de 
Since commit b4abf91047cf ("rtmutex: Make wait_lock irq safe") the
explanation in rcu_read_unlock() documentation about irq unsafe rtmutex
wait_lock is no longer valid.

Remove it to prevent kernel developers reading the documentation to rely on
it.

Suggested-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Anna-Maria Gleixner <anna-maria@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: bigeasy@linutronix.de
Link: https://lkml.kernel.org/r/20180525090507.22248-2-anna-maria@linutronix.de
rcu/x86: Provide early rcu_cpu_starting() callback 2018-05-22T23:12:26+00:00 Peter Zijlstra peterz@infradead.org 2018-05-22T16:50:53+00:00 f64c6013a2029316ea552f99823d116ee5f5f955 The x86/mtrr code does horrific things because hardware. It uses stop_machine_from_inactive_cpu(), which does a wakeup (of the stopper thread on another CPU), which uses RCU, all before the CPU is onlined. RCU complains about this, because wakeups use RCU and RCU does (rightfully) not consider offline CPUs for grace-periods. Fix this by initializing RCU way early in the MTRR case. Tested-by: Mike Galbraith <efault@gmx.de> Signed-off-by: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> [ paulmck: Add !SMP support, per 0day Test Robot report. ] 
The x86/mtrr code does horrific things because hardware. It uses
stop_machine_from_inactive_cpu(), which does a wakeup (of the stopper
thread on another CPU), which uses RCU, all before the CPU is onlined.

RCU complains about this, because wakeups use RCU and RCU does
(rightfully) not consider offline CPUs for grace-periods.

Fix this by initializing RCU way early in the MTRR case.

Tested-by: Mike Galbraith <efault@gmx.de>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
[ paulmck: Add !SMP support, per 0day Test Robot report. ]
rcu: Rename cond_resched_rcu_qs() to cond_resched_tasks_rcu_qs() 2018-05-15T17:27:29+00:00 Paul E. McKenney paulmck@linux.vnet.ibm.com 2018-03-03T00:35:27+00:00 cee4393989333795ae04dc9f3b83a578afe3fca6 Commit e31d28b6ab8f ("trace: Eliminate cond_resched_rcu_qs() in favor of cond_resched()") substituted cond_resched() for the earlier call to cond_resched_rcu_qs(). However, the new-age cond_resched() does not do anything to help RCU-tasks grace periods because (1) RCU-tasks is only enabled when CONFIG_PREEMPT=y and (2) cond_resched() is a complete no-op when preemption is enabled. This situation results in hangs when running the trace benchmarks. A number of potential fixes were discussed on LKML (https://lkml.kernel.org/r/20180224151240.0d63a059@vmware.local.home), including making cond_resched() not be a no-op; making cond_resched() not be a no-op, but only when running tracing benchmarks; reverting the aforementioned commit (which works because cond_resched_rcu_qs() does provide an RCU-tasks quiescent state; and adding a call to the scheduler/RCU rcu_note_voluntary_context_switch() function. All were deemed unsatisfactory, either due to added cond_resched() overhead or due to magic functions inviting cargo culting. This commit renames cond_resched_rcu_qs() to cond_resched_tasks_rcu_qs(), which provides a clear hint as to what this function is doing and why and where it should be used, and then replaces the call to cond_resched() with cond_resched_tasks_rcu_qs() in the trace benchmark's benchmark_event_kthread() function. Reported-by: Steven Rostedt <rostedt@goodmis.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Tested-by: Nicholas Piggin <npiggin@gmail.com> 
Commit e31d28b6ab8f ("trace: Eliminate cond_resched_rcu_qs() in favor
of cond_resched()") substituted cond_resched() for the earlier call
to cond_resched_rcu_qs().  However, the new-age cond_resched() does
not do anything to help RCU-tasks grace periods because (1) RCU-tasks
is only enabled when CONFIG_PREEMPT=y and (2) cond_resched() is a
complete no-op when preemption is enabled.  This situation results
in hangs when running the trace benchmarks.

A number of potential fixes were discussed on LKML
(https://lkml.kernel.org/r/20180224151240.0d63a059@vmware.local.home),
including making cond_resched() not be a no-op; making cond_resched()
not be a no-op, but only when running tracing benchmarks; reverting
the aforementioned commit (which works because cond_resched_rcu_qs()
does provide an RCU-tasks quiescent state; and adding a call to the
scheduler/RCU rcu_note_voluntary_context_switch() function.  All were
deemed unsatisfactory, either due to added cond_resched() overhead or
due to magic functions inviting cargo culting.

This commit renames cond_resched_rcu_qs() to cond_resched_tasks_rcu_qs(),
which provides a clear hint as to what this function is doing and
why and where it should be used, and then replaces the call to
cond_resched() with cond_resched_tasks_rcu_qs() in the trace benchmark's
benchmark_event_kthread() function.

Reported-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Tested-by: Nicholas Piggin <npiggin@gmail.com>
rcu: Fix init_rcu_head() comment. 2018-02-21T00:12:26+00:00 Paul E. McKenney paulmck@linux.vnet.ibm.com 2018-01-23T22:48:33+00:00 b5482a06593c851028b5dc061f9c8882bcc20008 The current (and implicit) comment header for init_rcu_head() and destroy_rcu_head() incorrectly says that they are not needed for statically allocated rcu_head structures. This commit therefore fixes this comment. Reported-by: Bart Van Assche <Bart.VanAssche@wdc.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Bart Van Assche <bart.vanassche@wdc.com> Reviewed-by: Leon Romanovsky <leonro@mellanox.com> 
The current (and implicit) comment header for init_rcu_head() and
destroy_rcu_head() incorrectly says that they are not needed for
statically allocated rcu_head structures.  This commit therefore
fixes this comment.

Reported-by: Bart Van Assche <Bart.VanAssche@wdc.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Bart Van Assche <bart.vanassche@wdc.com>
Reviewed-by: Leon Romanovsky <leonro@mellanox.com>
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 Paul E. McKenney paulmck@linux.vnet.ibm.com 2017-12-11T17:21:58+00:00 1dfa55e01987288d847220b8c027204871440ed1 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 
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: Adjust read-side accessor comments for READ_ONCE() 2017-12-04T18:52:53+00:00 Paul E. McKenney paulmck@linux.vnet.ibm.com 2017-10-09T17:30:58+00:00 137f61f6528f2bd552a75c59567d29db2857af97 Now that READ_ONCE() implies smp_read_barrier_depends(), the commit updates now-misleading comments to account for this change. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> 
Now that READ_ONCE() implies smp_read_barrier_depends(), the commit
updates now-misleading comments to account for this change.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>