Messages in this thread Patch in this message | | | From | "Paul E. McKenney" <> | Subject | [PATCH tip/core/rcu 02/14] notifiers: Apply ACCESS_ONCE() to avoid sparse false positive | Date | Fri, 15 Nov 2013 16:40:05 -0800 |
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From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
The sparse checking for rcu_assign_pointer() was recently upgraded to reject non-__kernel address spaces. This also rejects __rcu, which is almost always the right thing to do. However, the use in notifier_chain_unregister() is legitimate: It is deleting an element from an RCU-protected list, and all elements of this list are already visible to caller.
This commit therefore silences this false positive by laundering the pointer using ACCESS_ONCE() as suggested by Eric Dumazet and Josh Triplett.
Reported-by: kbuild test robot <fengguang.wu@intel.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> --- kernel/notifier.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/kernel/notifier.c b/kernel/notifier.c index 2d5cc4ccff7f..197eb70805a4 100644 --- a/kernel/notifier.c +++ b/kernel/notifier.c @@ -51,7 +51,8 @@ static int notifier_chain_unregister(struct notifier_block **nl, { while ((*nl) != NULL) { if ((*nl) == n) { - rcu_assign_pointer(*nl, n->next); + /* Both --rcu and visible, so ACCESS_ONCE() is OK. */ + ACCESS_ONCE(*nl) = n->next; return 0; } nl = &((*nl)->next); -- 1.8.1.5
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