[PATCH tip/core/rcu 0/2] SRCU changes for 3.11

[PATCH tip/core/rcu 0/2] SRCU changes for 3.11

[Paul E. McKenney]

Hello!

This series provides some SRCU changes:

1.	Remove srcu_read_lock_raw() and srcu_read_unlock_raw().  These
	never did get used, and have not been used for some time, so
	it is time for them to go.

2.	Fix a bug where srcu_read_lock() is not released upon return
	from kvmppc_hv_setup_htab_rma().

							Thanx, Paul


 b/Documentation/RCU/checklist.txt |    6 -----
 b/Documentation/RCU/torture.txt   |    6 -----
 b/Documentation/RCU/whatisRCU.txt |   22 ++++++-------------
 b/arch/powerpc/kvm/book3s_hv.c    |    2 -
 b/include/linux/srcu.h            |   43 --------------------------------------
 b/kernel/rcutorture.c             |   39 ----------------------------------
 6 files changed, 8 insertions(+), 110 deletions(-)

[PATCH tip/core/rcu 1/2] rcu: Remove srcu_read_lock_raw() and srcu_read_unlock_raw().

[Paul E. McKenney]

From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>

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

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
---
 Documentation/RCU/checklist.txt |  6 ------
 Documentation/RCU/torture.txt   |  6 ------
 Documentation/RCU/whatisRCU.txt | 22 +++++++--------------
 include/linux/srcu.h            | 43 -----------------------------------------
 kernel/rcutorture.c             | 39 -------------------------------------
 5 files changed, 7 insertions(+), 109 deletions(-)

diff --git a/Documentation/RCU/checklist.txt b/Documentation/RCU/checklist.txt
index 79e789b8..7703ec7 100644
--- a/Documentation/RCU/checklist.txt
+++ b/Documentation/RCU/checklist.txt
@@ -354,12 +354,6 @@ over a rather long period of time, but improvements are always welcome!
 	using RCU rather than SRCU, because RCU is almost always faster
 	and easier to use than is SRCU.
 
-	If you need to enter your read-side critical section in a
-	hardirq or exception handler, and then exit that same read-side
-	critical section in the task that was interrupted, then you need
-	to srcu_read_lock_raw() and srcu_read_unlock_raw(), which avoid
-	the lockdep checking that would otherwise this practice illegal.
-
 	Also unlike other forms of RCU, explicit initialization
 	and cleanup is required via init_srcu_struct() and
 	cleanup_srcu_struct().	These are passed a "struct srcu_struct"
diff --git a/Documentation/RCU/torture.txt b/Documentation/RCU/torture.txt
index 7dce8a1..d8a5023 100644
--- a/Documentation/RCU/torture.txt
+++ b/Documentation/RCU/torture.txt
@@ -182,12 +182,6 @@ torture_type	The type of RCU to test, with string values as follows:
 		"srcu_expedited": srcu_read_lock(), srcu_read_unlock() and
 			synchronize_srcu_expedited().
 
-		"srcu_raw": srcu_read_lock_raw(), srcu_read_unlock_raw(),
-			and call_srcu().
-
-		"srcu_raw_sync": srcu_read_lock_raw(), srcu_read_unlock_raw(),
-			and synchronize_srcu().
-
 		"sched": preempt_disable(), preempt_enable(), and
 			call_rcu_sched().
 
diff --git a/Documentation/RCU/whatisRCU.txt b/Documentation/RCU/whatisRCU.txt
index 10df0b8..0f0fb7c 100644
--- a/Documentation/RCU/whatisRCU.txt
+++ b/Documentation/RCU/whatisRCU.txt
@@ -842,9 +842,7 @@ SRCU:	Critical sections	Grace period		Barrier
 
 	srcu_read_lock		synchronize_srcu	srcu_barrier
 	srcu_read_unlock	call_srcu
-	srcu_read_lock_raw	synchronize_srcu_expedited
-	srcu_read_unlock_raw
-	srcu_dereference
+	srcu_dereference	synchronize_srcu_expedited
 
 SRCU:	Initialization/cleanup
 	init_srcu_struct
@@ -865,38 +863,32 @@ list can be helpful:
 
 a.	Will readers need to block?  If so, you need SRCU.
 
-b.	Is it necessary to start a read-side critical section in a
-	hardirq handler or exception handler, and then to complete
-	this read-side critical section in the task that was
-	interrupted?  If so, you need SRCU's srcu_read_lock_raw() and
-	srcu_read_unlock_raw() primitives.
-
-c.	What about the -rt patchset?  If readers would need to block
+b.	What about the -rt patchset?  If readers would need to block
 	in an non-rt kernel, you need SRCU.  If readers would block
 	in a -rt kernel, but not in a non-rt kernel, SRCU is not
 	necessary.
 
-d.	Do you need to treat NMI handlers, hardirq handlers,
+c.	Do you need to treat NMI handlers, hardirq handlers,
 	and code segments with preemption disabled (whether
 	via preempt_disable(), local_irq_save(), local_bh_disable(),
 	or some other mechanism) as if they were explicit RCU readers?
 	If so, RCU-sched is the only choice that will work for you.
 
-e.	Do you need RCU grace periods to complete even in the face
+d.	Do you need RCU grace periods to complete even in the face
 	of softirq monopolization of one or more of the CPUs?  For
 	example, is your code subject to network-based denial-of-service
 	attacks?  If so, you need RCU-bh.
 
-f.	Is your workload too update-intensive for normal use of
+e.	Is your workload too update-intensive for normal use of
 	RCU, but inappropriate for other synchronization mechanisms?
 	If so, consider SLAB_DESTROY_BY_RCU.  But please be careful!
 
-g.	Do you need read-side critical sections that are respected
+f.	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.
 
-h.	Otherwise, use RCU.
+g.	Otherwise, use RCU.
 
 Of course, this all assumes that you have determined that RCU is in fact
 the right tool for your job.
diff --git a/include/linux/srcu.h b/include/linux/srcu.h
index 04f4121..c114614 100644
--- a/include/linux/srcu.h
+++ b/include/linux/srcu.h
@@ -237,47 +237,4 @@ static inline void srcu_read_unlock(struct srcu_struct *sp, int idx)
 	__srcu_read_unlock(sp, idx);
 }
 
-/**
- * srcu_read_lock_raw - register a new reader for an SRCU-protected structure.
- * @sp: srcu_struct in which to register the new reader.
- *
- * Enter an SRCU read-side critical section.  Similar to srcu_read_lock(),
- * but avoids the RCU-lockdep checking.  This means that it is legal to
- * use srcu_read_lock_raw() in one context, for example, in an exception
- * handler, and then have the matching srcu_read_unlock_raw() in another
- * context, for example in the task that took the exception.
- *
- * However, the entire SRCU read-side critical section must reside within a
- * single task.  For example, beware of using srcu_read_lock_raw() in
- * a device interrupt handler and srcu_read_unlock() in the interrupted
- * task:  This will not work if interrupts are threaded.
- */
-static inline int srcu_read_lock_raw(struct srcu_struct *sp)
-{
-	unsigned long flags;
-	int ret;
-
-	local_irq_save(flags);
-	ret =  __srcu_read_lock(sp);
-	local_irq_restore(flags);
-	return ret;
-}
-
-/**
- * srcu_read_unlock_raw - unregister reader from an SRCU-protected structure.
- * @sp: srcu_struct in which to unregister the old reader.
- * @idx: return value from corresponding srcu_read_lock_raw().
- *
- * Exit an SRCU read-side critical section without lockdep-RCU checking.
- * See srcu_read_lock_raw() for more details.
- */
-static inline void srcu_read_unlock_raw(struct srcu_struct *sp, int idx)
-{
-	unsigned long flags;
-
-	local_irq_save(flags);
-	__srcu_read_unlock(sp, idx);
-	local_irq_restore(flags);
-}
-
 #endif
diff --git a/kernel/rcutorture.c b/kernel/rcutorture.c
index e1f3a8c..b1fa551 100644
--- a/kernel/rcutorture.c
+++ b/kernel/rcutorture.c
@@ -695,44 +695,6 @@ static struct rcu_torture_ops srcu_sync_ops = {
 	.name		= "srcu_sync"
 };
 
-static int srcu_torture_read_lock_raw(void) __acquires(&srcu_ctl)
-{
-	return srcu_read_lock_raw(&srcu_ctl);
-}
-
-static void srcu_torture_read_unlock_raw(int idx) __releases(&srcu_ctl)
-{
-	srcu_read_unlock_raw(&srcu_ctl, idx);
-}
-
-static struct rcu_torture_ops srcu_raw_ops = {
-	.init		= rcu_sync_torture_init,
-	.readlock	= srcu_torture_read_lock_raw,
-	.read_delay	= srcu_read_delay,
-	.readunlock	= srcu_torture_read_unlock_raw,
-	.completed	= srcu_torture_completed,
-	.deferred_free	= srcu_torture_deferred_free,
-	.sync		= srcu_torture_synchronize,
-	.call		= NULL,
-	.cb_barrier	= NULL,
-	.stats		= srcu_torture_stats,
-	.name		= "srcu_raw"
-};
-
-static struct rcu_torture_ops srcu_raw_sync_ops = {
-	.init		= rcu_sync_torture_init,
-	.readlock	= srcu_torture_read_lock_raw,
-	.read_delay	= srcu_read_delay,
-	.readunlock	= srcu_torture_read_unlock_raw,
-	.completed	= srcu_torture_completed,
-	.deferred_free	= rcu_sync_torture_deferred_free,
-	.sync		= srcu_torture_synchronize,
-	.call		= NULL,
-	.cb_barrier	= NULL,
-	.stats		= srcu_torture_stats,
-	.name		= "srcu_raw_sync"
-};
-
 static void srcu_torture_synchronize_expedited(void)
 {
 	synchronize_srcu_expedited(&srcu_ctl);
@@ -1983,7 +1945,6 @@ rcu_torture_init(void)
 		{ &rcu_ops, &rcu_sync_ops, &rcu_expedited_ops,
 		  &rcu_bh_ops, &rcu_bh_sync_ops, &rcu_bh_expedited_ops,
 		  &srcu_ops, &srcu_sync_ops, &srcu_expedited_ops,
-		  &srcu_raw_ops, &srcu_raw_sync_ops,
 		  &sched_ops, &sched_sync_ops, &sched_expedited_ops, };
 
 	mutex_lock(&fullstop_mutex);
-- 
1.8.1.5

[PATCH tip/core/rcu 2/2] powerpc,kvm: Fix unbalanced srcu_read_[un]lock()

[Paul E. McKenney]

From: Lai Jiangshan <laijs@cn.fujitsu.com>

At the up_out: label in kvmppc_hv_setup_htab_rma(), srcu_read_lock()
is still held.  This commit therefore have to releases it before return.

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Gleb Natapov <gleb@redhat.com>
Cc: Alexander Graf <agraf@suse.de>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: kvm@vger.kernel.org
Cc: kvm-ppc@vger.kernel.org
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 arch/powerpc/kvm/book3s_hv.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index 80dcc53..c26740e 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c
@@ -1799,7 +1799,7 @@ static int kvmppc_hv_setup_htab_rma(struct kvm_vcpu *vcpu)
 
  up_out:
 	up_read(&current->mm->mmap_sem);
-	goto out;
+	goto out_srcu;
 }
 
 int kvmppc_core_init_vm(struct kvm *kvm)
-- 
1.8.1.5

[PATCH tip/core/rcu 2/2] powerpc,kvm: Fix unbalanced srcu_read_[un]lock()

[Paul E. McKenney]

From: Lai Jiangshan <laijs@cn.fujitsu.com>

At the up_out: label in kvmppc_hv_setup_htab_rma(), srcu_read_lock()
is still held.  This commit therefore have to releases it before return.

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Gleb Natapov <gleb@redhat.com>
Cc: Alexander Graf <agraf@suse.de>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: kvm@vger.kernel.org
Cc: kvm-ppc@vger.kernel.org
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 arch/powerpc/kvm/book3s_hv.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index 80dcc53..c26740e 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c
@@ -1799,7 +1799,7 @@ static int kvmppc_hv_setup_htab_rma(struct kvm_vcpu *vcpu)
 
  up_out:
 	up_read(&current->mm->mmap_sem);
-	goto out;
+	goto out_srcu;
 }
 
 int kvmppc_core_init_vm(struct kvm *kvm)
-- 
1.8.1.5

Re: [PATCH tip/core/rcu 0/2] SRCU changes for 3.11

[Josh Triplett]

On Fri, Apr 12, 2013 at 04:38:15PM -0700, Paul E. McKenney wrote:
> Hello!
> 
> This series provides some SRCU changes:
> 
> 1.	Remove srcu_read_lock_raw() and srcu_read_unlock_raw().  These
> 	never did get used, and have not been used for some time, so
> 	it is time for them to go.
> 
> 2.	Fix a bug where srcu_read_lock() is not released upon return
> 	from kvmppc_hv_setup_htab_rma().

For both:
Reviewed-by: Josh Triplett <josh@joshtriplett.org>