[PATCH] carl9170: tx: Replace rcu_assign_pointer() with RCU_INIT_POINTER()

From: Andreea-Cristina Bernat
Date: Wed Aug 27 2014 - 09:27:50 EST

According to RCU_INIT_POINTER()'s block comment 3.a, it can be used if
"3. The referenced data structure has already been exposed to readers either
at compile time or via rcu_assign_pointer() -and-
a. You have not made -any- reader-visible changes to this structure since

This case fulfills the conditions above because between the rcu_dereference()
call (cvif = rcu_dereference(ar->beacon_iter);) and the rcu_assign_pointer()
call there is no update of the "cvif" variable.
Therefore, this patch makes the replacement.

The following Coccinelle semantic patch was used:
identifier v;

v = rcu_dereference(...);
... when != rcu_dereference(...);
when != v = ...;
when != (<+...v...+>)++;
when != \(memcpy\|memset\)(...);
- rcu_assign_pointer
(..., v);
if(...) {
... when != v = ...;
- rcu_assign_pointer
(..., v);
... when any

Because there are cases where between a ârcu_dereference()â call and a
ârcu_assign_pointer()â call might be updates of the value that interests us,
the Coccinelle semantic patch ignores them and replaces with
"RCU_INIT_POINTER()" only when the update is not happening.

Signed-off-by: Andreea-Cristina Bernat <bernat.ada@xxxxxxxxx>
drivers/net/wireless/ath/carl9170/tx.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/wireless/ath/carl9170/tx.c b/drivers/net/wireless/ath/carl9170/tx.c
index 4cadfd4..ae86a600 100644
--- a/drivers/net/wireless/ath/carl9170/tx.c
+++ b/drivers/net/wireless/ath/carl9170/tx.c
@@ -1557,7 +1557,7 @@ static struct carl9170_vif_info *carl9170_pick_beaconing_vif(struct ar9170 *ar)

- rcu_assign_pointer(ar->beacon_iter, cvif);
+ RCU_INIT_POINTER(ar->beacon_iter, cvif);
return cvif;


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