linux-toradex.git/include/linux/srcu.h, branch v4.6-rc3

rcu: Document unique-name limitation for DEFINE_STATIC_SRCU()

2016-02-24T03:59:55+00:00

SRCU uses per-CPU variables, and DEFINE_STATIC_SRCU() uses a static
per-CPU variable.  However, per-CPU variables have significant
restrictions, for example, names of per-CPU variables must be globally
unique, even if declared static.  These restrictions carry over to
DEFINE_STATIC_SRCU(), and this commit therefore documents these
restrictions.

Reported-by: Stephen Rothwell 
Reported-by: kbuild test robot 
Suggested-by: Boqun Feng 
Signed-off-by: Paul E. McKenney 
Reviewed-by: Tejun Heo

rcu: Move preemption disabling out of __srcu_read_lock()

2015-10-06T18:15:43+00:00

Currently, __srcu_read_lock() cannot be invoked from restricted
environments because it contains calls to preempt_disable() and
preempt_enable(), both of which can invoke lockdep, which is a bad
idea in some restricted execution modes.  This commit therefore moves
the preempt_disable() and preempt_enable() from __srcu_read_lock()
to srcu_read_lock().  It also inserts the preempt_disable() and
preempt_enable() around the call to __srcu_read_lock() in do_exit().

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

rcu: Reverse rcu_dereference_check() conditions

2015-03-03T19:16:47+00:00

The rcu_dereference_check() family of primitives evaluates the RCU
lockdep expression first, and only then evaluates the expression passed
in.  This works fine normally, but can potentially fail in environments
(such as NMI handlers) where lockdep cannot be invoked.  The problem is
that even if the expression passed in is "1", the compiler would need to
prove that the RCU lockdep expression (rcu_read_lock_held(), for example)
is free of side effects in order to be able to elide it.  Given that
rcu_read_lock_held() is sometimes separately compiled, the compiler cannot
always use this optimization.

This commit therefore reverse the order of evaluation, so that the
expression passed in is evaluated first, and the RCU lockdep expression is
evaluated only if the passed-in expression evaluated to false, courtesy
of the C-language short-circuit boolean evaluation rules.  This compells
the compiler to forego executing the RCU lockdep expression in cases
where the passed-in expression evaluates to "1" at compile time, so that
(for example) rcu_dereference_raw() can be guaranteed to execute safely
within an NMI handler.

Signed-off-by: Paul E. McKenney 
Acked-by: Peter Zijlstra (Intel)

rcu: Combine DEFINE_SRCU() and DEFINE_STATIC_SRCU()

2015-01-06T19:04:27+00:00

The DEFINE_SRCU() and DEFINE_STATIC_SRCU() definitions are quite
similar, so this commit combines them, saving a bit of code and removing
redundancy.

Signed-off-by: Paul E. McKenney

rcu: Expand SRCU ->completed to 64 bits

2015-01-06T19:04:26+00:00

When rcutorture used only the low-order 32 bits of the grace-period
number, it was not a problem for SRCU to use a 32-bit completed field.
However, rcutorture now uses the full 64 bits on 64-bit systems, so
this commit converts SRCU's ->completed field to unsigned long so as to
provide 64 bits on 64-bit systems.

Signed-off-by: Paul E. McKenney

rcu: Stop tracking FSF's postal address

2014-02-17T23:01:37+00:00

All of the RCU source files have the usual GPL header, which contains a
long-obsolete postal address for FSF.  To avoid the need to track the
FSF office's movements, this commit substitutes the URL where GPL may
be found.

Reported-by: Greg KH 
Reported-by: Steven Rostedt 
Signed-off-by: Paul E. McKenney 
Reviewed-by: Josh Triplett

srcu: API for barrier after srcu read unlock

2013-11-06T07:32:09+00:00

srcu read lock/unlock include a full memory barrier
but that's an implementation detail.
Add an API for make memory fencing explicit for
users that need this barrier, to make sure we
can change it as needed without breaking all users.

Acked-by: "Paul E. McKenney" 
Reviewed-by: Paul E. McKenney 
Signed-off-by: Michael S. Tsirkin 
Signed-off-by: Gleb Natapov

rcu: Remove srcu_read_lock_raw() and srcu_read_unlock_raw().

2013-06-10T20:45:25+00:00

These interfaces never did get used, so this commit removes them,
their rcutorture tests, and documentation referencing them.

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

srcu: Remove checks preventing idle CPUs from calling srcu_read_lock()

2013-02-07T23:15:00+00:00

SRCU has its own statemachine and no longer relies on normal RCU.
Its read-side critical section can now be used by an offline CPU, so this
commit removes the check and the comments, reverting the SRCU portion
of ff195cb6 (rcu: Warn when srcu_read_lock() is used in an extended
quiescent state).

It also makes the codes match the comments in whatisRCU.txt:

g.	Do you need read-side critical sections that are respected
	even though they are in the middle of the idle loop, during
	user-mode execution, or on an offlined CPU?  If so, SRCU is the
	only choice that will work for you.

[ paulmck: There is at least one remaining issue, namely use of lockdep
	   with tracing enabled. ]

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

srcu: Remove checks preventing offline CPUs from calling srcu_read_lock()

2013-02-07T23:10:39+00:00

SRCU has its own statemachine and no longer relies on normal RCU.
Its read-side critical section can now be used by an offline CPU, so this
commit removes the check and the comments, reverting the SRCU portion
of c0d6d01b (rcu: Check for illegal use of RCU from offlined CPUs).

It also makes the code match the comments in whatisRCU.txt:

g.	Do you need read-side critical sections that are respected
	even though they are in the middle of the idle loop, during
	user-mode execution, or on an offlined CPU?  If so, SRCU is the
	only choice that will work for you.

[ paulmck: There is at least one remaining issue, namely use of lockdep
	   with tracing enabled. ]

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