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Author SHA1 Message Date
Paul E. McKenney
632ee20013 rcu: Introduce lockdep-based checking to RCU read-side primitives
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>
2010-02-25 09:40:59 +01:00
Paul E. McKenney
017c426138 rcu: Fix sparse warnings
Rename local variable "i" in rcu_init() to avoid conflict with
RCU_INIT_FLAVOR(), restrict the scope of RCU_TREE_NONCORE, and
make __synchronize_srcu() static.

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: <12635142581560-git-send-email->
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2010-01-16 10:25:22 +01:00
Paul E. McKenney
0cd397d336 rcu: Add synchronize_srcu_expedited()
This patch creates a synchronize_srcu_expedited() that uses
synchronize_sched_expedited() where synchronize_srcu()
uses synchronize_sched().  The synchronize_srcu() and
synchronize_srcu_expedited() functions become one-liners that
pass synchronize_sched() or synchronize_sched_expedited(),
repectively, to a new __synchronize_srcu() function.

While in the file, move the EXPORT_SYMBOL_GPL()s to immediately
follow the corresponding functions.

Requested-by: Avi Kivity <avi@redhat.com>
Tested-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.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: dhowells@redhat.com
Cc: avi@redhat.com
LKML-Reference: <12565226354038-git-send-email->
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2009-10-26 09:40:30 +01:00
Adrian Bunk
bb695170d8 make srcu_readers_active() static
Make the needlessly global srcu_readers_active() static.

Signed-off-by: Adrian Bunk <bunk@kernel.org>
Cc: "Paul E. McKenney" <paulmck@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2008-02-06 10:41:02 -08:00
Alan Stern
e6a92013ba [PATCH] SRCU: report out-of-memory errors
Currently the init_srcu_struct() routine has no way to report out-of-memory
errors.  This patch (as761) makes it return -ENOMEM when the per-cpu data
allocation fails.

The patch also makes srcu_init_notifier_head() report a BUG if a notifier
head can't be initialized.  Perhaps it should return -ENOMEM instead, but
in the most likely cases where this might occur I don't think any recovery
is possible.  Notifier chains generally are not created dynamically.

[akpm@osdl.org: avoid statement-with-side-effect in macro]
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Acked-by: Paul E. McKenney <paulmck@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-10-04 07:55:30 -07:00
Paul E. McKenney
621934ee7e [PATCH] srcu-3: RCU variant permitting read-side blocking
Updated patch adding a variant of RCU that permits sleeping in read-side
critical sections.  SRCU is as follows:

o	Each use of SRCU creates its own srcu_struct, and each
	srcu_struct has its own set of grace periods.  This is
	critical, as it prevents one subsystem with a blocking
	reader from holding up SRCU grace periods for other
	subsystems.

o	The SRCU primitives (srcu_read_lock(), srcu_read_unlock(),
	and synchronize_srcu()) all take a pointer to a srcu_struct.

o	The SRCU primitives must be called from process context.

o	srcu_read_lock() returns an int that must be passed to
	the matching srcu_read_unlock().  Realtime RCU avoids the
	need for this by storing the state in the task struct,
	but SRCU needs to allow a given code path to pass through
	multiple SRCU domains -- storing state in the task struct
	would therefore require either arbitrary space in the
	task struct or arbitrary limits on SRCU nesting.  So I
	kicked the state-storage problem up to the caller.

	Of course, it is not permitted to call synchronize_srcu()
	while in an SRCU read-side critical section.

o	There is no call_srcu().  It would not be hard to implement
	one, but it seems like too easy a way to OOM the system.
	(Hey, we have enough trouble with call_rcu(), which does
	-not- permit readers to sleep!!!)  So, if you want it,
	please tell me why...

[josht@us.ibm.com: sparse notation]
Signed-off-by: Paul E. McKenney <paulmck@us.ibm.com>
Signed-off-by: Josh Triplett <josh@freedesktop.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-10-04 07:55:30 -07:00