[tip:sched/core] sched: Fix static_key race with sched_feat()
From: tip-bot for Jason Baron
Date: Wed Jul 16 2014 - 15:24:50 EST
Commit-ID: 5cd08fbfdb6baa9fe98f530b76898fc5725a6289
Gitweb: http://git.kernel.org/tip/5cd08fbfdb6baa9fe98f530b76898fc5725a6289
Author: Jason Baron <jbaron@xxxxxxxxxx>
AuthorDate: Wed, 2 Jul 2014 15:52:44 +0000
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
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@xxxxxxxxxxxxxx>
Signed-off-by: Jason Baron <jbaron@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: rostedt@xxxxxxxxxxx
Link: http://lkml.kernel.org/r/9d7780c83db26683955cd01e6bc654ee2586e67f.1404315388.git.jbaron@xxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
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;
--
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