As suggested by Linus, push the irqs_disabled() down to the
rcu_read_lock_bh_held() level so that all callers get the benefit
of the correct check.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This commit provides definitions for the __rcu annotation defined earlier.
This annotation permits sparse to check for correct use of RCU-protected
pointers. If a pointer that is annotated with __rcu is accessed
directly (as opposed to via rcu_dereference(), rcu_assign_pointer(),
or one of their variants), sparse can be made to complain. To enable
such complaints, use the new default-disabled CONFIG_SPARSE_RCU_POINTER
kernel configuration option. Please note that these sparse complaints are
intended to be a debugging aid, -not- a code-style-enforcement mechanism.
There are special rcu_dereference_protected() and rcu_access_pointer()
accessors for use when RCU read-side protection is not required, for
example, when no other CPU has access to the data structure in question
or while the current CPU hold the update-side lock.
This patch also updates a number of docbook comments that were showing
their age.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Christopher Li <sparse@chrisli.org>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
Helps finding racy users of call_rcu(), which results in hangs because list
entries are overwritten and/or skipped.
Changelog since v4:
- Bissectability is now OK
- Now generate a WARN_ON_ONCE() for non-initialized rcu_head passed to
call_rcu(). Statically initialized objects are detected with
object_is_static().
- Rename rcu_head_init_on_stack to init_rcu_head_on_stack.
- Remove init_rcu_head() completely.
Changelog since v3:
- Include comments from Lai Jiangshan
This new patch version is based on the debugobjects with the newly introduced
"active state" tracker.
Non-initialized entries are all considered as "statically initialized". An
activation fixup (triggered by call_rcu()) takes care of performing the debug
object initialization without issuing any warning. Since we cannot increase the
size of struct rcu_head, I don't see much room to put an identifier for
statically initialized rcu_head structures. So for now, we have to live without
"activation without explicit init" detection. But the main purpose of this debug
option is to detect double-activations (double call_rcu() use of a rcu_head
before the callback is executed), which is correctly addressed here.
This also detects potential internal RCU callback corruption, which would cause
the callbacks to be executed twice.
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
CC: David S. Miller <davem@davemloft.net>
CC: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
CC: akpm@linux-foundation.org
CC: mingo@elte.hu
CC: laijs@cn.fujitsu.com
CC: dipankar@in.ibm.com
CC: josh@joshtriplett.org
CC: dvhltc@us.ibm.com
CC: niv@us.ibm.com
CC: tglx@linutronix.de
CC: peterz@infradead.org
CC: rostedt@goodmis.org
CC: Valdis.Kletnieks@vt.edu
CC: dhowells@redhat.com
CC: eric.dumazet@gmail.com
CC: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
TINY_RCU does not need rcu_scheduler_active unless CONFIG_DEBUG_LOCK_ALLOC.
So conditionally compile rcu_scheduler_active in order to slim down
rcutiny a bit more. Also gets rid of an EXPORT_SYMBOL_GPL, which is
responsible for most of the slimming.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Some RCU-lockdep splat repairs need to know whether they are running
in a single-threaded process. Unfortunately, the thread_group_empty()
primitive is defined in sched.h, and can induce #include hell. This
commit therefore introduces a rcu_my_thread_group_empty() wrapper that
is defined in rcupdate.c, thus avoiding the need to include sched.h
everywhere.
Signed-off-by: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Inspection is proving insufficient to catch all RCU misuses,
which is understandable given that rcu_dereference() might be
protected by any of four different flavors of RCU (RCU, RCU-bh,
RCU-sched, and SRCU), and might also/instead be protected by any
of a number of locking primitives. It is therefore time to
enlist the aid of lockdep.
This set of patches is inspired by earlier work by Peter
Zijlstra and Thomas Gleixner, and takes the following approach:
o Set up separate lockdep classes for RCU, RCU-bh, and RCU-sched.
o Set up separate lockdep classes for each instance of SRCU.
o Create primitives that check for being in an RCU read-side
critical section. These return exact answers if lockdep is
fully enabled, but if unsure, report being in an RCU read-side
critical section. (We want to avoid false positives!)
The primitives are:
For RCU: rcu_read_lock_held(void)
For RCU-bh: rcu_read_lock_bh_held(void)
For RCU-sched: rcu_read_lock_sched_held(void)
For SRCU: srcu_read_lock_held(struct srcu_struct *sp)
o Add rcu_dereference_check(), which takes a second argument
in which one places a boolean expression based on the above
primitives and/or lockdep_is_held().
o A new kernel configuration parameter, CONFIG_PROVE_RCU, enables
rcu_dereference_check(). This depends on CONFIG_PROVE_LOCKING,
and should be quite helpful during the transition period while
CONFIG_PROVE_RCU-unaware patches are in flight.
The existing rcu_dereference() primitive does no checking, but
upcoming patches will change that.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: mathieu.desnoyers@polymtl.ca
Cc: josh@joshtriplett.org
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: peterz@infradead.org
Cc: rostedt@goodmis.org
Cc: Valdis.Kletnieks@vt.edu
Cc: dhowells@redhat.com
LKML-Reference: <1266887105-1528-1-git-send-email-paulmck@linux.vnet.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This patch is a version of RCU designed for !SMP provided for a
small-footprint RCU implementation. In particular, the
implementation of synchronize_rcu() is extremely lightweight and
high performance. It passes rcutorture testing in each of the
four relevant configurations (combinations of NO_HZ and PREEMPT)
on x86. This saves about 1K bytes compared to old Classic RCU
(which is no longer in mainline), and more than three kilobytes
compared to Hierarchical RCU (updated to 2.6.30):
CONFIG_TREE_RCU:
text data bss dec filename
183 4 0 187 kernel/rcupdate.o
2783 520 36 3339 kernel/rcutree.o
3526 Total (vs 4565 for v7)
CONFIG_TREE_PREEMPT_RCU:
text data bss dec filename
263 4 0 267 kernel/rcupdate.o
4594 776 52 5422 kernel/rcutree.o
5689 Total (6155 for v7)
CONFIG_TINY_RCU:
text data bss dec filename
96 4 0 100 kernel/rcupdate.o
734 24 0 758 kernel/rcutiny.o
858 Total (vs 848 for v7)
The above is for x86. Your mileage may vary on other platforms.
Further compression is possible, but is being procrastinated.
Changes from v7 (http://lkml.org/lkml/2009/10/9/388)
o Apply Lai Jiangshan's review comments (aside from
might_sleep() in synchronize_sched(), which is covered by SMP builds).
o Fix up expedited primitives.
Changes from v6 (http://lkml.org/lkml/2009/9/23/293).
o Forward ported to put it into the 2.6.33 stream.
o Added lockdep support.
o Make lightweight rcu_barrier.
Changes from v5 (http://lkml.org/lkml/2009/6/23/12).
o Ported to latest pre-2.6.32 merge window kernel.
- Renamed rcu_qsctr_inc() to rcu_sched_qs().
- Renamed rcu_bh_qsctr_inc() to rcu_bh_qs().
- Provided trivial rcu_cpu_notify().
- Provided trivial exit_rcu().
- Provided trivial rcu_needs_cpu().
- Fixed up the rcu_*_enter/exit() functions in linux/hardirq.h.
o Removed the dependence on EMBEDDED, with a view to making
TINY_RCU default for !SMP at some time in the future.
o Added (trivial) support for expedited grace periods.
Changes from v4 (http://lkml.org/lkml/2009/5/2/91) include:
o Squeeze the size down a bit further by removing the
->completed field from struct rcu_ctrlblk.
o This permits synchronize_rcu() to become the empty function.
Previous concerns about rcutorture were unfounded, as
rcutorture correctly handles a constant value from
rcu_batches_completed() and rcu_batches_completed_bh().
Changes from v3 (http://lkml.org/lkml/2009/3/29/221) include:
o Changed rcu_batches_completed(), rcu_batches_completed_bh()
rcu_enter_nohz(), rcu_exit_nohz(), rcu_nmi_enter(), and
rcu_nmi_exit(), to be static inlines, as suggested by David
Howells. Doing this saves about 100 bytes from rcutiny.o.
(The numbers between v3 and this v4 of the patch are not directly
comparable, since they are against different versions of Linux.)
Changes from v2 (http://lkml.org/lkml/2009/2/3/333) include:
o Fix whitespace issues.
o Change short-circuit "||" operator to instead be "+" in order
to fix performance bug noted by "kraai" on LWN.
(http://lwn.net/Articles/324348/)
Changes from v1 (http://lkml.org/lkml/2009/1/13/440) include:
o This version depends on EMBEDDED as well as !SMP, as suggested
by Ingo.
o Updated rcu_needs_cpu() to unconditionally return zero,
permitting the CPU to enter dynticks-idle mode at any time.
This works because callbacks can be invoked upon entry to
dynticks-idle mode.
o Paul is now OK with this being included, based on a poll at
the Kernel Miniconf at linux.conf.au, where about ten people said
that they cared about saving 900 bytes on single-CPU systems.
o Applies to both mainline and tip/core/rcu.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: David Howells <dhowells@redhat.com>
Acked-by: Josh Triplett <josh@joshtriplett.org>
Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Cc: dipankar@in.ibm.com
Cc: mathieu.desnoyers@polymtl.ca
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: peterz@infradead.org
Cc: rostedt@goodmis.org
Cc: Valdis.Kletnieks@vt.edu
Cc: avi@redhat.com
Cc: mtosatti@redhat.com
LKML-Reference: <12565226351355-git-send-email->
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Move the rcu_lock_map definition from rcutree.c to rcupdate.c so that
TINY_RCU can use lockdep.
Reported-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Don't try and predeclare inline funcs like this:
static inline void wait_migrated_callbacks(void)
...
static void _rcu_barrier(enum rcu_barrier type)
{
...
wait_migrated_callbacks();
}
...
static inline void wait_migrated_callbacks(void)
{
wait_event(rcu_migrate_wq, !atomic_read(&rcu_migrate_type_count));
}
as it upsets some versions of gcc under some circumstances:
kernel/rcupdate.c: In function `_rcu_barrier':
kernel/rcupdate.c:125: sorry, unimplemented: inlining failed in call to 'wait_migrated_callbacks': function body not available
kernel/rcupdate.c:152: sorry, unimplemented: called from here
This can be dealt with by simply putting the static variables (rcu_migrate_*)
at the top, and moving the implementation of the function up so that it
replaces its forward declaration.
Signed-off-by: David Howells <dhowells@redhat.com>
Cc: Dipankar Sarma <dipankar@in.ibm.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
cpu hotplug may happen asynchronously, some rcu callbacks are maybe
still on dead cpu, rcu_barrier() also needs to wait for these rcu
callbacks to complete, so we must ensure callbacks in dead cpu are
migrated to online cpu.
Paul E. McKenney's review:
Good stuff, Lai!!! Simpler than any of the approaches that I was
considering, and, better yet, independent of the underlying RCU
implementation!!!
I was initially worried that wake_up() might wake only one of two
possible wait_event()s, namely rcu_barrier() and the CPU_POST_DEAD code,
but the fact that wait_event() clears WQ_FLAG_EXCLUSIVE avoids that issue.
I was also worried about the fact that different RCU implementations have
different mappings of call_rcu(), call_rcu_bh(), and call_rcu_sched(), but
this is OK as well because we just get an extra (harmless) callback in the
case that they map together (for example, Classic RCU has call_rcu_sched()
mapping to call_rcu()).
Overlap of CPU-hotplug operations is prevented by cpu_add_remove_lock,
and any stray callbacks that arrive (for example, from irq handlers
running on the dying CPU) either are ahead of the CPU_DYING callbacks on
the one hand (and thus accounted for), or happened after the rcu_barrier()
started on the other (and thus don't need to be accounted for).
Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Reviewed-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
LKML-Reference: <49C36476.1010400@cn.fujitsu.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
