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rcu: Avoid ->dynticks_nmi_nesting store tearing

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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@linux.vnet.ibm.com>
This commit is contained in:
Paul E. McKenney 2017-10-02 16:54:49 -07:00
parent 4fbd8d194f
commit 2e672ab2d4
1 changed files with 5 additions and 3 deletions
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8
kernel/rcu/tree.c
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@ -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();
}