Commit-ID: 2e672ab2d491713541963afca3a5967ccc2376e9
Gitweb: https://git.kernel.org/tip/2e672ab2d491713541963afca3a5967ccc2376e9
Author: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
AuthorDate: Mon, 2 Oct 2017 16:54:49 -0700
Committer: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
CommitDate: Mon, 27 Nov 2017 08:40:09 -0800
rcu: Avoid ->dynticks_nmi_nesting store tearing
NMIs can nest, and store tearing could in theory happen on carries
from one byte to the next. This commit therefore adds the WRITE_ONCE()
macros preventing this.
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
---
kernel/rcu/tree.c | 8 +++++---
1 file changed, 5 insertions(+), 3 deletions(-)
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index f9c0ca2..c5d960f 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -1103,7 +1103,8 @@ void rcu_nmi_enter(void)
rcu_dynticks_eqs_exit();
incby = 1;
}
- rdtp->dynticks_nmi_nesting += incby;
+ WRITE_ONCE(rdtp->dynticks_nmi_nesting, /* Prevent store tearing. */
+ rdtp->dynticks_nmi_nesting + incby);
barrier();
}
@@ -1135,12 +1136,13 @@ void rcu_nmi_exit(void)
* leave it in non-RCU-idle state.
*/
if (rdtp->dynticks_nmi_nesting != 1) {
- rdtp->dynticks_nmi_nesting -= 2;
+ WRITE_ONCE(rdtp->dynticks_nmi_nesting, /* No store tearing. */
+ rdtp->dynticks_nmi_nesting - 2);
return;
}
/* This NMI interrupted an RCU-idle CPU, restore RCU-idleness. */
- rdtp->dynticks_nmi_nesting = 0;
+ WRITE_ONCE(rdtp->dynticks_nmi_nesting, 0); /* Avoid store tearing. */
rcu_dynticks_eqs_enter();
}
--
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