[PATCH] sched: Use RCU read lock on all calls to dl_bw_of()

[PATCH] sched: Use RCU read lock on all calls to dl_bw_of()

[Sasha Levin]

Commit "sched: Use dl_bw_of() under RCU read lock" has missed a call
to dl_bw_of(), which has now started showing warnings:

[  820.960972] ===============================
[  820.961663] [ INFO: suspicious RCU usage. ]
[  820.962344] 3.17.0-rc6-next-20140926-sasha-00051-g9253dff-dirty #1242 Not tainted
[  820.963670] -------------------------------
[  820.964454] kernel/sched/core.c:2008 sched RCU must be held!
[  820.975556]
[  820.975556] other info that might help us debug this:
[  820.975556]
[  820.987512] rcu_scheduler_active = 1, debug_locks = 1
[  820.988546] 9 locks held by trinity-c157/26236:
[  820.989274] #0: (&f->f_pos_lock){+.+.+.}, at: __fdget_pos (fs/file.c:718)
[  820.994630] #1: (sb_writers#5){.+.+.+}, at: do_readv_writev (include/linux/fs.h:2270 fs/read_write.c:832)
[  820.996170] #2: (&of->mutex){+.+.+.}, at: kernfs_fop_write (fs/kernfs/file.c:296)
[  821.001816] #3: (s_active#23){.+.+.+}, at: kernfs_fop_write (fs/kernfs/file.c:296)
[  821.003235] #4: (device_hotplug_lock){+.+.+.}, at: lock_device_hotplug_sysfs (drivers/base/core.c:66)
[  821.004842] #5: (&dev->mutex){......}, at: device_offline (include/linux/device.h:900 drivers/base/core.c:1423)
[  821.010610] #6: (cpu_add_remove_lock){+.+.+.}, at: cpu_down (kernel/cpu.c:426)
[  821.011859] #7: (cpu_hotplug.lock){++++++}, at: cpu_hotplug_begin (kernel/cpu.c:152)
[  821.013208] #8: (cpu_hotplug.lock#2){+.+.+.}, at: cpu_hotplug_begin (kernel/cpu.c:158)
[  821.027101]
[  821.027101] stack backtrace:
[  821.027903] CPU: 17 PID: 26236 Comm: trinity-c157 Not tainted 3.17.0-rc6-next-20140926-sasha-00051-g9253dff-dirty #1242
[  821.030246]  0000000000000001 0000000000000000 0000000000000001 ffff880803363a98
[  821.038543]  ffffffffb5f0070f 0000000000000011 ffff8808271eb000 ffff880803363ac8
[  821.039967]  ffffffffb124e8ed 0000000000000000 ffff880803363bbc 0000000000000013
[  821.041455] Call Trace:
[  821.042038] dump_stack (lib/dump_stack.c:52)
[  821.043005] lockdep_rcu_suspicious (kernel/locking/lockdep.c:4265)
[  821.044169] sched_cpu_inactive (kernel/sched/core.c:2008 kernel/sched/core.c:5271)
[  821.050486] notifier_call_chain (kernel/notifier.c:93)
[  821.051594] __raw_notifier_call_chain (kernel/notifier.c:395)
[  821.052766] _cpu_down (include/linux/notifier.h:179 kernel/cpu.c:219 kernel/cpu.c:356)
[  821.053809] ? cpu_down (kernel/cpu.c:426)
[  821.054770] cpu_down (kernel/cpu.c:431)
[  821.062497] cpu_subsys_offline (drivers/base/cpu.c:69)
[  821.063500] device_offline (drivers/base/core.c:1428)
[  821.064428] ? cpu_device_release (drivers/base/cpu.c:67)
[  821.065429] online_store (drivers/base/core.c:451 (discriminator 2))
[  821.066390] dev_attr_store (drivers/base/core.c:138)
[  821.067328] ? dev_driver_string (drivers/base/core.c:130)
[  821.073698] sysfs_kf_write (fs/sysfs/file.c:116)
[  821.074496] ? sysfs_file_ops (fs/sysfs/file.c:108)
[  821.075312] kernfs_fop_write (fs/kernfs/file.c:308)
[  821.076135] ? do_readv_writev (include/linux/fs.h:2270 fs/read_write.c:832)
[  821.076999] do_loop_readv_writev (fs/read_write.c:710)
[  821.078066] ? kernfs_vma_page_mkwrite (fs/kernfs/file.c:267)
[  821.079252] do_readv_writev (fs/read_write.c:842)
[  821.080495] ? kernfs_vma_page_mkwrite (fs/kernfs/file.c:267)
[  821.081644] ? mutex_lock_nested (./arch/x86/include/asm/preempt.h:98 kernel/locking/mutex.c:599 kernel/locking/mutex.c:616)
[  821.086535] ? __fdget_pos (fs/file.c:718)
[  821.087447] ? __fdget_pos (fs/file.c:718)
[  821.088363] ? rcu_read_lock_held (kernel/rcu/update.c:169)
[  821.089425] vfs_writev (fs/read_write.c:881)
[  821.090486] SyS_writev (fs/read_write.c:913 fs/read_write.c:905)
[  821.091382] tracesys_phase2 (arch/x86/kernel/entry_64.S:529)

Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
---
 kernel/sched/core.c |   15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index e6cfd9b..91bfbbb 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -5261,6 +5261,9 @@ static int sched_cpu_inactive(struct notifier_block *nfb,
 {
 	unsigned long flags;
 	long cpu = (long)hcpu;
+	int ret;
+
+	rcu_read_lock();
 
 	switch (action & ~CPU_TASKS_FROZEN) {
 	case CPU_DOWN_PREPARE:
@@ -5277,13 +5280,19 @@ static int sched_cpu_inactive(struct notifier_block *nfb,
 			overflow = __dl_overflow(dl_b, cpus, 0, 0);
 			raw_spin_unlock_irqrestore(&dl_b->lock, flags);
 
+			ret = notifier_from_errno(-EBUSY);
 			if (overflow)
-				return notifier_from_errno(-EBUSY);
+				goto done;
 		}
-		return NOTIFY_OK;
+		ret = NOTIFY_OK;
+		goto done;
 	}
 
-	return NOTIFY_DONE;
+	ret = NOTIFY_DONE;
+
+done:
+	rcu_read_unlock();
+	return ret;
 }
 
 static int __init migration_init(void)
-- 
1.7.10.4

Re: [PATCH] sched: Use RCU read lock on all calls to dl_bw_of()

[Kirill Tkhai]

Hi, Sasha,

В Пн, 29/09/2014 в 11:19 -0400, Sasha Levin пишет:
> Commit "sched: Use dl_bw_of() under RCU read lock" has missed a call
> to dl_bw_of(), which has now started showing warnings:
> 
> [  820.960972] ===============================
> [  820.961663] [ INFO: suspicious RCU usage. ]
> [  820.962344] 3.17.0-rc6-next-20140926-sasha-00051-g9253dff-dirty #1242 Not tainted
> [  820.963670] -------------------------------
> [  820.964454] kernel/sched/core.c:2008 sched RCU must be held!
> [  820.975556]
> [  820.975556] other info that might help us debug this:
> [  820.975556]
> [  820.987512] rcu_scheduler_active = 1, debug_locks = 1
> [  820.988546] 9 locks held by trinity-c157/26236:
> [  820.989274] #0: (&f->f_pos_lock){+.+.+.}, at: __fdget_pos (fs/file.c:718)
> [  820.994630] #1: (sb_writers#5){.+.+.+}, at: do_readv_writev (include/linux/fs.h:2270 fs/read_write.c:832)
> [  820.996170] #2: (&of->mutex){+.+.+.}, at: kernfs_fop_write (fs/kernfs/file.c:296)
> [  821.001816] #3: (s_active#23){.+.+.+}, at: kernfs_fop_write (fs/kernfs/file.c:296)
> [  821.003235] #4: (device_hotplug_lock){+.+.+.}, at: lock_device_hotplug_sysfs (drivers/base/core.c:66)
> [  821.004842] #5: (&dev->mutex){......}, at: device_offline (include/linux/device.h:900 drivers/base/core.c:1423)
> [  821.010610] #6: (cpu_add_remove_lock){+.+.+.}, at: cpu_down (kernel/cpu.c:426)
> [  821.011859] #7: (cpu_hotplug.lock){++++++}, at: cpu_hotplug_begin (kernel/cpu.c:152)
> [  821.013208] #8: (cpu_hotplug.lock#2){+.+.+.}, at: cpu_hotplug_begin (kernel/cpu.c:158)
> [  821.027101]
> [  821.027101] stack backtrace:
> [  821.027903] CPU: 17 PID: 26236 Comm: trinity-c157 Not tainted 3.17.0-rc6-next-20140926-sasha-00051-g9253dff-dirty #1242
> [  821.030246]  0000000000000001 0000000000000000 0000000000000001 ffff880803363a98
> [  821.038543]  ffffffffb5f0070f 0000000000000011 ffff8808271eb000 ffff880803363ac8
> [  821.039967]  ffffffffb124e8ed 0000000000000000 ffff880803363bbc 0000000000000013
> [  821.041455] Call Trace:
> [  821.042038] dump_stack (lib/dump_stack.c:52)
> [  821.043005] lockdep_rcu_suspicious (kernel/locking/lockdep.c:4265)
> [  821.044169] sched_cpu_inactive (kernel/sched/core.c:2008 kernel/sched/core.c:5271)
> [  821.050486] notifier_call_chain (kernel/notifier.c:93)
> [  821.051594] __raw_notifier_call_chain (kernel/notifier.c:395)
> [  821.052766] _cpu_down (include/linux/notifier.h:179 kernel/cpu.c:219 kernel/cpu.c:356)
> [  821.053809] ? cpu_down (kernel/cpu.c:426)
> [  821.054770] cpu_down (kernel/cpu.c:431)
> [  821.062497] cpu_subsys_offline (drivers/base/cpu.c:69)
> [  821.063500] device_offline (drivers/base/core.c:1428)
> [  821.064428] ? cpu_device_release (drivers/base/cpu.c:67)
> [  821.065429] online_store (drivers/base/core.c:451 (discriminator 2))
> [  821.066390] dev_attr_store (drivers/base/core.c:138)
> [  821.067328] ? dev_driver_string (drivers/base/core.c:130)
> [  821.073698] sysfs_kf_write (fs/sysfs/file.c:116)
> [  821.074496] ? sysfs_file_ops (fs/sysfs/file.c:108)
> [  821.075312] kernfs_fop_write (fs/kernfs/file.c:308)
> [  821.076135] ? do_readv_writev (include/linux/fs.h:2270 fs/read_write.c:832)
> [  821.076999] do_loop_readv_writev (fs/read_write.c:710)
> [  821.078066] ? kernfs_vma_page_mkwrite (fs/kernfs/file.c:267)
> [  821.079252] do_readv_writev (fs/read_write.c:842)
> [  821.080495] ? kernfs_vma_page_mkwrite (fs/kernfs/file.c:267)
> [  821.081644] ? mutex_lock_nested (./arch/x86/include/asm/preempt.h:98 kernel/locking/mutex.c:599 kernel/locking/mutex.c:616)
> [  821.086535] ? __fdget_pos (fs/file.c:718)
> [  821.087447] ? __fdget_pos (fs/file.c:718)
> [  821.088363] ? rcu_read_lock_held (kernel/rcu/update.c:169)
> [  821.089425] vfs_writev (fs/read_write.c:881)
> [  821.090486] SyS_writev (fs/read_write.c:913 fs/read_write.c:905)
> [  821.091382] tracesys_phase2 (arch/x86/kernel/entry_64.S:529)
> 
> Signed-off-by: Sasha Levin <sasha.levin@oracle.com>

Thanks for your report. It looks like your fix is not enough, because
we check for rcu_read_lock_sched_held() in dl_bw_of(). It still warns
even if rcu_read_lock() is held.

I used rcu_read_lock_sched_held() because we free root_domain using
call_rcu_sched(). So, it's necessary to held rcu_read_lock_sched(),
and my initial commit has this problem too.

It looks like we should fix it in a way like this:

[PATCH]sched: Use dl_bw_of() under rcu_read_lock_sched()

rq->rd is freed using call_rcu_sched(), and it's accessed with preemption
disabled in the most cases.

So in other places we should use rcu_read_lock_sched() to access it to fit
the scheme:

rcu_read_lock_sched() or preempt_disable() <==> call_rcu_sched().

Signed-off-by: Kirill Tkhai <ktkhai@parallels.com
Fixes 66339c31bc39 "sched: Use dl_bw_of() under RCU read lock"
Reported-by: Sasha Levin <sasha.levin@oracle.com>
---
 kernel/sched/core.c | 23 ++++++++++++++++-------
 1 file changed, 16 insertions(+), 7 deletions(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 25e4513..3a0a62d 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -5248,6 +5248,9 @@ static int sched_cpu_inactive(struct notifier_block *nfb,
 {
 	unsigned long flags;
 	long cpu = (long)hcpu;
+	int ret;
+
+	rcu_read_lock_sched();
 
 	switch (action & ~CPU_TASKS_FROZEN) {
 	case CPU_DOWN_PREPARE:
@@ -5264,13 +5267,19 @@ static int sched_cpu_inactive(struct notifier_block *nfb,
 			overflow = __dl_overflow(dl_b, cpus, 0, 0);
 			raw_spin_unlock_irqrestore(&dl_b->lock, flags);
 
+			ret = notifier_from_errno(-EBUSY);
 			if (overflow)
-				return notifier_from_errno(-EBUSY);
+				goto done;
 		}
-		return NOTIFY_OK;
+		ret = NOTIFY_OK;
+		goto done;
 	}
 
-	return NOTIFY_DONE;
+	ret = NOTIFY_DONE;
+
+done:
+	rcu_read_unlock_sched();
+	return ret;
 }
 
 static int __init migration_init(void)
@@ -7634,7 +7643,7 @@ static int sched_dl_global_constraints(void)
 	int cpu, ret = 0;
 	unsigned long flags;
 
-	rcu_read_lock();
+	rcu_read_lock_sched();
 
 	/*
 	 * Here we want to check the bandwidth not being set to some
@@ -7657,7 +7666,7 @@ static int sched_dl_global_constraints(void)
 			break;
 	}
 
-	rcu_read_unlock();
+	rcu_read_unlock_sched();
 
 	return ret;
 }
@@ -7674,7 +7683,7 @@ static void sched_dl_do_global(void)
 	if (global_rt_runtime() != RUNTIME_INF)
 		new_bw = to_ratio(global_rt_period(), global_rt_runtime());
 
-	rcu_read_lock();
+	rcu_read_lock_sched();
 	/*
 	 * FIXME: As above...
 	 */
@@ -7685,7 +7694,7 @@ static void sched_dl_do_global(void)
 		dl_b->bw = new_bw;
 		raw_spin_unlock_irqrestore(&dl_b->lock, flags);
 	}
-	rcu_read_unlock();
+	rcu_read_unlock_sched();
 }
 
 static int sched_rt_global_validate(void)

Re: [PATCH] sched: Use RCU read lock on all calls to dl_bw_of()

[Peter Zijlstra]

On Mon, Sep 29, 2014 at 08:43:47PM +0400, Kirill Tkhai wrote:
> Thanks for your report. It looks like your fix is not enough, because
> we check for rcu_read_lock_sched_held() in dl_bw_of(). It still warns
> even if rcu_read_lock() is held.
> 
> I used rcu_read_lock_sched_held() because we free root_domain using
> call_rcu_sched(). So, it's necessary to held rcu_read_lock_sched(),
> and my initial commit has this problem too.
> 
> It looks like we should fix it in a way like this:
> 
> [PATCH]sched: Use dl_bw_of() under rcu_read_lock_sched()
> 
> rq->rd is freed using call_rcu_sched(), and it's accessed with preemption
> disabled in the most cases.
> 
> So in other places we should use rcu_read_lock_sched() to access it to fit
> the scheme:
> 
> rcu_read_lock_sched() or preempt_disable() <==> call_rcu_sched().

Hmm, sad that. I cannot remember why that is rcu_sched, I suspect
because we rely on it someplace but I cannot remember where.

We could of course do a double take on that and use call_rcu after
call_rcu_sched(), such that either or both are sufficient.

I would very much prefer not to add extra preempt_disable()s if
possible.

Re: [PATCH] sched: Use RCU read lock on all calls to dl_bw_of()

[Peter Zijlstra]

On Mon, Sep 29, 2014 at 06:54:18PM +0200, Peter Zijlstra wrote:
> On Mon, Sep 29, 2014 at 08:43:47PM +0400, Kirill Tkhai wrote:
> > Thanks for your report. It looks like your fix is not enough, because
> > we check for rcu_read_lock_sched_held() in dl_bw_of(). It still warns
> > even if rcu_read_lock() is held.
> > 
> > I used rcu_read_lock_sched_held() because we free root_domain using
> > call_rcu_sched(). So, it's necessary to held rcu_read_lock_sched(),
> > and my initial commit has this problem too.
> > 
> > It looks like we should fix it in a way like this:
> > 
> > [PATCH]sched: Use dl_bw_of() under rcu_read_lock_sched()
> > 
> > rq->rd is freed using call_rcu_sched(), and it's accessed with preemption
> > disabled in the most cases.
> > 
> > So in other places we should use rcu_read_lock_sched() to access it to fit
> > the scheme:
> > 
> > rcu_read_lock_sched() or preempt_disable() <==> call_rcu_sched().
> 
> Hmm, sad that. I cannot remember why that is rcu_sched, I suspect
> because we rely on it someplace but I cannot remember where.
> 
> We could of course do a double take on that and use call_rcu after
> call_rcu_sched(), such that either or both are sufficient.
> 
> I would very much prefer not to add extra preempt_disable()s if
> possible.

Ah wait, if we simply move that preempt_disable() inside the
for_each_cpu() loop there's no harm done. Having them outside is painful
though.

Re: [PATCH] sched: Use RCU read lock on all calls to dl_bw_of()

[Kirill Tkhai]

В Пн, 29/09/2014 в 19:00 +0200, Peter Zijlstra пишет:
> On Mon, Sep 29, 2014 at 06:54:18PM +0200, Peter Zijlstra wrote:
> > On Mon, Sep 29, 2014 at 08:43:47PM +0400, Kirill Tkhai wrote:
> > > Thanks for your report. It looks like your fix is not enough, because
> > > we check for rcu_read_lock_sched_held() in dl_bw_of(). It still warns
> > > even if rcu_read_lock() is held.
> > > 
> > > I used rcu_read_lock_sched_held() because we free root_domain using
> > > call_rcu_sched(). So, it's necessary to held rcu_read_lock_sched(),
> > > and my initial commit has this problem too.
> > > 
> > > It looks like we should fix it in a way like this:
> > > 
> > > [PATCH]sched: Use dl_bw_of() under rcu_read_lock_sched()
> > > 
> > > rq->rd is freed using call_rcu_sched(), and it's accessed with preemption
> > > disabled in the most cases.
> > > 
> > > So in other places we should use rcu_read_lock_sched() to access it to fit
> > > the scheme:
> > > 
> > > rcu_read_lock_sched() or preempt_disable() <==> call_rcu_sched().
> > 
> > Hmm, sad that. I cannot remember why that is rcu_sched, I suspect
> > because we rely on it someplace but I cannot remember where.
> > 
> > We could of course do a double take on that and use call_rcu after
> > call_rcu_sched(), such that either or both are sufficient.
> > 
> > I would very much prefer not to add extra preempt_disable()s if
> > possible.
> 
> Ah wait, if we simply move that preempt_disable() inside the
> for_each_cpu() loop there's no harm done. Having them outside is painful
> though.

[PATCH]sched: Use dl_bw_of() under preempt_disable()

rq->rd is freed using call_rcu_sched(), so rcu_read_lock() to access it
is not enough. We should use either rcu_read_lock_sched() or preempt_disable().

We choose preempt_disable()/preempt_enable() like in other places
where rq->rd is used.

Signed-off-by: Kirill Tkhai <ktkhai@parallels.com
Fixes 66339c31bc39 "sched: Use dl_bw_of() under RCU read lock"
Reported-by: Sasha Levin <sasha.levin@oracle.com>
Suggested-by: Peter Zijlstra <peterz@infradead.org>
---
 kernel/sched/core.c | 25 ++++++++++++++++---------
 1 file changed, 16 insertions(+), 9 deletions(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 25e4513..e1a4d76 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -5248,6 +5248,7 @@ static int sched_cpu_inactive(struct notifier_block *nfb,
 {
 	unsigned long flags;
 	long cpu = (long)hcpu;
+	struct dl_bw *dl_b;
 
 	switch (action & ~CPU_TASKS_FROZEN) {
 	case CPU_DOWN_PREPARE:
@@ -5255,15 +5256,19 @@ static int sched_cpu_inactive(struct notifier_block *nfb,
 
 		/* explicitly allow suspend */
 		if (!(action & CPU_TASKS_FROZEN)) {
-			struct dl_bw *dl_b = dl_bw_of(cpu);
 			bool overflow;
 			int cpus;
 
+			preempt_disable();
+			dl_b = dl_bw_of(cpu);
+
 			raw_spin_lock_irqsave(&dl_b->lock, flags);
 			cpus = dl_bw_cpus(cpu);
 			overflow = __dl_overflow(dl_b, cpus, 0, 0);
 			raw_spin_unlock_irqrestore(&dl_b->lock, flags);
 
+			preempt_enable();
+
 			if (overflow)
 				return notifier_from_errno(-EBUSY);
 		}
@@ -7631,11 +7636,10 @@ static int sched_dl_global_constraints(void)
 	u64 runtime = global_rt_runtime();
 	u64 period = global_rt_period();
 	u64 new_bw = to_ratio(period, runtime);
+	struct dl_bw *dl_b;
 	int cpu, ret = 0;
 	unsigned long flags;
 
-	rcu_read_lock();
-
 	/*
 	 * Here we want to check the bandwidth not being set to some
 	 * value smaller than the currently allocated bandwidth in
@@ -7646,25 +7650,27 @@ static int sched_dl_global_constraints(void)
 	 * solutions is welcome!
 	 */
 	for_each_possible_cpu(cpu) {
-		struct dl_bw *dl_b = dl_bw_of(cpu);
+		preempt_disable();
+		dl_b = dl_bw_of(cpu);
 
 		raw_spin_lock_irqsave(&dl_b->lock, flags);
 		if (new_bw < dl_b->total_bw)
 			ret = -EBUSY;
 		raw_spin_unlock_irqrestore(&dl_b->lock, flags);
 
+		preempt_enable();
+
 		if (ret)
 			break;
 	}
 
-	rcu_read_unlock();
-
 	return ret;
 }
 
 static void sched_dl_do_global(void)
 {
 	u64 new_bw = -1;
+	struct dl_bw *dl_b;
 	int cpu;
 	unsigned long flags;
 
@@ -7674,18 +7680,19 @@ static void sched_dl_do_global(void)
 	if (global_rt_runtime() != RUNTIME_INF)
 		new_bw = to_ratio(global_rt_period(), global_rt_runtime());
 
-	rcu_read_lock();
 	/*
 	 * FIXME: As above...
 	 */
 	for_each_possible_cpu(cpu) {
-		struct dl_bw *dl_b = dl_bw_of(cpu);
+		preempt_disable();
+		dl_b = dl_bw_of(cpu);
 
 		raw_spin_lock_irqsave(&dl_b->lock, flags);
 		dl_b->bw = new_bw;
 		raw_spin_unlock_irqrestore(&dl_b->lock, flags);
+
+		preempt_enable();
 	}
-	rcu_read_unlock();
 }
 
 static int sched_rt_global_validate(void)

Re: [PATCH] sched: Use RCU read lock on all calls to dl_bw_of()

[Peter Zijlstra]

On Tue, Sep 30, 2014 at 12:23:37PM +0400, Kirill Tkhai wrote:
> [PATCH]sched: Use dl_bw_of() under preempt_disable()
> 
> rq->rd is freed using call_rcu_sched(), so rcu_read_lock() to access it
> is not enough. We should use either rcu_read_lock_sched() or preempt_disable().
> 
> We choose preempt_disable()/preempt_enable() like in other places
> where rq->rd is used.

I changed it to rcu_read_lock_sched(), but no biggie, thanks!

[tip:sched/core] sched/dl: Use dl_bw_of() under rcu_read_lock_sched()

[tip-bot for Kirill Tkhai]

Commit-ID:  f10e00f4bf360c36edbe6bf18a6c75b171cbe012
Gitweb:     http://git.kernel.org/tip/f10e00f4bf360c36edbe6bf18a6c75b171cbe012
Author:     Kirill Tkhai <ktkhai@parallels.com>
AuthorDate: Tue, 30 Sep 2014 12:23:37 +0400
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Fri, 3 Oct 2014 05:46:58 +0200

sched/dl: Use dl_bw_of() under rcu_read_lock_sched()

rq->rd is freed using call_rcu_sched(), so rcu_read_lock() to access it
is not enough. We should use either rcu_read_lock_sched() or preempt_disable().

Reported-by: Sasha Levin <sasha.levin@oracle.com>
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Kirill Tkhai <ktkhai@parallels.com
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Fixes: 66339c31bc39 "sched: Use dl_bw_of() under RCU read lock"
Link: http://lkml.kernel.org/r/1412065417.20287.24.camel@tkhai
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 kernel/sched/core.c | 25 ++++++++++++++++---------
 1 file changed, 16 insertions(+), 9 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index b5349fe..c84bdc0 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -5264,6 +5264,7 @@ static int sched_cpu_inactive(struct notifier_block *nfb,
 {
 	unsigned long flags;
 	long cpu = (long)hcpu;
+	struct dl_bw *dl_b;
 
 	switch (action & ~CPU_TASKS_FROZEN) {
 	case CPU_DOWN_PREPARE:
@@ -5271,15 +5272,19 @@ static int sched_cpu_inactive(struct notifier_block *nfb,
 
 		/* explicitly allow suspend */
 		if (!(action & CPU_TASKS_FROZEN)) {
-			struct dl_bw *dl_b = dl_bw_of(cpu);
 			bool overflow;
 			int cpus;
 
+			rcu_read_lock_sched();
+			dl_b = dl_bw_of(cpu);
+
 			raw_spin_lock_irqsave(&dl_b->lock, flags);
 			cpus = dl_bw_cpus(cpu);
 			overflow = __dl_overflow(dl_b, cpus, 0, 0);
 			raw_spin_unlock_irqrestore(&dl_b->lock, flags);
 
+			rcu_read_unlock_sched();
+
 			if (overflow)
 				return notifier_from_errno(-EBUSY);
 		}
@@ -7647,11 +7652,10 @@ static int sched_dl_global_constraints(void)
 	u64 runtime = global_rt_runtime();
 	u64 period = global_rt_period();
 	u64 new_bw = to_ratio(period, runtime);
+	struct dl_bw *dl_b;
 	int cpu, ret = 0;
 	unsigned long flags;
 
-	rcu_read_lock();
-
 	/*
 	 * Here we want to check the bandwidth not being set to some
 	 * value smaller than the currently allocated bandwidth in
@@ -7662,25 +7666,27 @@ static int sched_dl_global_constraints(void)
 	 * solutions is welcome!
 	 */
 	for_each_possible_cpu(cpu) {
-		struct dl_bw *dl_b = dl_bw_of(cpu);
+		rcu_read_lock_sched();
+		dl_b = dl_bw_of(cpu);
 
 		raw_spin_lock_irqsave(&dl_b->lock, flags);
 		if (new_bw < dl_b->total_bw)
 			ret = -EBUSY;
 		raw_spin_unlock_irqrestore(&dl_b->lock, flags);
 
+		rcu_read_unlock_sched();
+
 		if (ret)
 			break;
 	}
 
-	rcu_read_unlock();
-
 	return ret;
 }
 
 static void sched_dl_do_global(void)
 {
 	u64 new_bw = -1;
+	struct dl_bw *dl_b;
 	int cpu;
 	unsigned long flags;
 
@@ -7690,18 +7696,19 @@ static void sched_dl_do_global(void)
 	if (global_rt_runtime() != RUNTIME_INF)
 		new_bw = to_ratio(global_rt_period(), global_rt_runtime());
 
-	rcu_read_lock();
 	/*
 	 * FIXME: As above...
 	 */
 	for_each_possible_cpu(cpu) {
-		struct dl_bw *dl_b = dl_bw_of(cpu);
+		rcu_read_lock_sched();
+		dl_b = dl_bw_of(cpu);
 
 		raw_spin_lock_irqsave(&dl_b->lock, flags);
 		dl_b->bw = new_bw;
 		raw_spin_unlock_irqrestore(&dl_b->lock, flags);
+
+		rcu_read_unlock_sched();
 	}
-	rcu_read_unlock();
 }
 
 static int sched_rt_global_validate(void)