[PATCH 0/2] sched: static_key sched_feat race + cleanup

[PATCH 0/2] sched: static_key sched_feat race + cleanup

[Jason Baron]

Hi,

Andi Kleen previously pointed out a get/set race in the sched_feat()
infrastructure. I had previously proposed to address this with a new
static_key set_true/set_false API:

http://www.gossamer-threads.com/lists/linux/kernel/1955879

However, I think its simpler to just add higher level locking as
Ingo previously suggested, and that is how other consumers of the
this interface are already operating. It seems a bit like overkill
to add this new API, just for this one case.

So, this locking change is in patch 2. Patch 1 is a small cleanup, but
no functional change.
 
Thanks,

-Jason

Jason Baron (2):
  sched: remove extra static_key function indirection
  sched: fix static_key race with sched_feat

 kernel/sched/core.c  |  5 +++++
 kernel/sched/sched.h | 12 +-----------
 2 files changed, 6 insertions(+), 11 deletions(-)

-- 
1.8.2.rc2

[PATCH 1/2] sched: remove extra static_key function indirection

[Jason Baron]

I think its a bit simpler without having to follow an extra layer of static
inline fuctions. No functional change just cosmetic.

Signed-off-by: Jason Baron <jbaron@akamai.com>
---
 kernel/sched/sched.h | 12 +-----------
 1 file changed, 1 insertion(+), 11 deletions(-)

diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 31cc02e..10494c0 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -884,20 +884,10 @@ enum {
 #undef SCHED_FEAT
 
 #if defined(CONFIG_SCHED_DEBUG) && defined(HAVE_JUMP_LABEL)
-static __always_inline bool static_branch__true(struct static_key *key)
-{
-	return static_key_true(key); /* Not out of line branch. */
-}
-
-static __always_inline bool static_branch__false(struct static_key *key)
-{
-	return static_key_false(key); /* Out of line branch. */
-}
-
 #define SCHED_FEAT(name, enabled)					\
 static __always_inline bool static_branch_##name(struct static_key *key) \
 {									\
-	return static_branch__##enabled(key);				\
+	return static_key_##enabled(key);				\
 }
 
 #include "features.h"
-- 
1.8.2.rc2

[PATCH 2/2] sched: fix static_key race with sched_feat

[Jason Baron]

As pointed out by Andi Kleen, the usage of static keys can be racy in
sched_feat_disable() vs. sched_feat_enable(). Currently, we first check the
value of keys->enabled, and subsequently update the branch direction. This,
can be racy and can potentially leave the keys in an inconsistent state.

Take the i_mutex around these calls to resolve the race.

Reported-by: Andi Kleen <andi@firstfloor.org>
Signed-off-by: Jason Baron <jbaron@akamai.com>
---
 kernel/sched/core.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 3bdf01b..249c865 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -243,6 +243,7 @@ sched_feat_write(struct file *filp, const char __user *ubuf,
 	char buf[64];
 	char *cmp;
 	int i;
+	struct inode *inode;
 
 	if (cnt > 63)
 		cnt = 63;
@@ -253,7 +254,11 @@ sched_feat_write(struct file *filp, const char __user *ubuf,
 	buf[cnt] = 0;
 	cmp = strstrip(buf);
 
+	/* Ensure the static_key remains in a consistent state */
+	inode = file_inode(filp);
+	mutex_lock(&inode->i_mutex);
 	i = sched_feat_set(cmp);
+	mutex_unlock(&inode->i_mutex);
 	if (i == __SCHED_FEAT_NR)
 		return -EINVAL;
 
-- 
1.8.2.rc2

[tip:sched/core] sched: Remove extra static_key*() function indirection

[tip-bot for Jason Baron]

Commit-ID:  6e76ea8a8209386c3cc7ee5594e6ea5d25525cf2
Gitweb:     http://git.kernel.org/tip/6e76ea8a8209386c3cc7ee5594e6ea5d25525cf2
Author:     Jason Baron <jbaron@akamai.com>
AuthorDate: Wed, 2 Jul 2014 15:52:41 +0000
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Wed, 16 Jul 2014 13:38:20 +0200

sched: Remove extra static_key*() function indirection

I think its a bit simpler without having to follow an extra layer of static
inline fuctions. No functional change just cosmetic.

Signed-off-by: Jason Baron <jbaron@akamai.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: rostedt@goodmis.org
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/2ce52233ce200faad93b6029d90f1411cd926667.1404315388.git.jbaron@akamai.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 kernel/sched/sched.h | 12 +-----------
 1 file changed, 1 insertion(+), 11 deletions(-)

diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 1283945..579712f 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -887,20 +887,10 @@ enum {
 #undef SCHED_FEAT
 
 #if defined(CONFIG_SCHED_DEBUG) && defined(HAVE_JUMP_LABEL)
-static __always_inline bool static_branch__true(struct static_key *key)
-{
-	return static_key_true(key); /* Not out of line branch. */
-}
-
-static __always_inline bool static_branch__false(struct static_key *key)
-{
-	return static_key_false(key); /* Out of line branch. */
-}
-
 #define SCHED_FEAT(name, enabled)					\
 static __always_inline bool static_branch_##name(struct static_key *key) \
 {									\
-	return static_branch__##enabled(key);				\
+	return static_key_##enabled(key);				\
 }
 
 #include "features.h"

[tip:sched/core] sched: Fix static_key race with sched_feat()

[tip-bot for Jason Baron]

Commit-ID:  5cd08fbfdb6baa9fe98f530b76898fc5725a6289
Gitweb:     http://git.kernel.org/tip/5cd08fbfdb6baa9fe98f530b76898fc5725a6289
Author:     Jason Baron <jbaron@akamai.com>
AuthorDate: Wed, 2 Jul 2014 15:52:44 +0000
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Wed, 16 Jul 2014 13:38:21 +0200

sched: Fix static_key race with sched_feat()

As pointed out by Andi Kleen, the usage of static keys can be racy in
sched_feat_disable() vs. sched_feat_enable(). Currently, we first check the
value of keys->enabled, and subsequently update the branch direction. This,
can be racy and can potentially leave the keys in an inconsistent state.

Take the i_mutex around these calls to resolve the race.

Reported-by: Andi Kleen <andi@firstfloor.org>
Signed-off-by: Jason Baron <jbaron@akamai.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: rostedt@goodmis.org
Link: http://lkml.kernel.org/r/9d7780c83db26683955cd01e6bc654ee2586e67f.1404315388.git.jbaron@akamai.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 kernel/sched/core.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 2f96081..8705125 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -245,6 +245,7 @@ sched_feat_write(struct file *filp, const char __user *ubuf,
 	char buf[64];
 	char *cmp;
 	int i;
+	struct inode *inode;
 
 	if (cnt > 63)
 		cnt = 63;
@@ -255,7 +256,11 @@ sched_feat_write(struct file *filp, const char __user *ubuf,
 	buf[cnt] = 0;
 	cmp = strstrip(buf);
 
+	/* Ensure the static_key remains in a consistent state */
+	inode = file_inode(filp);
+	mutex_lock(&inode->i_mutex);
 	i = sched_feat_set(cmp);
+	mutex_unlock(&inode->i_mutex);
 	if (i == __SCHED_FEAT_NR)
 		return -EINVAL;