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authorDavid Woodhouse <David.Woodhouse@intel.com>2012-11-28 10:15:05 (GMT)
committerDavid Woodhouse <David.Woodhouse@intel.com>2012-12-02 00:05:20 (GMT)
commit5b4d72080f49498d2390563aa90f5bc31785406c (patch)
tree62da5867de0ff07672d07687adee6ce7bb9388af /net/atm/pppoatm.c
parent9eba25268e5862571d53122065616c456fe1142a (diff)
pppoatm: optimise PPP channel wakeups after sock_owned_by_user()
We don't need to schedule the wakeup tasklet on *every* unlock; only if we actually blocked the channel in the first place. Signed-off-by: David Woodhouse <David.Woodhouse@intel.com> Acked-by: Krzysztof Mazur <krzysiek@podlesie.net>
Diffstat (limited to 'net/atm/pppoatm.c')
-rw-r--r--net/atm/pppoatm.c21
1 files changed, 19 insertions, 2 deletions
diff --git a/net/atm/pppoatm.c b/net/atm/pppoatm.c
index 9fcda8c..8c93267 100644
--- a/net/atm/pppoatm.c
+++ b/net/atm/pppoatm.c
@@ -113,7 +113,17 @@ static void pppoatm_release_cb(struct atm_vcc *atmvcc)
{
struct pppoatm_vcc *pvcc = atmvcc_to_pvcc(atmvcc);
- tasklet_schedule(&pvcc->wakeup_tasklet);
+ /*
+ * As in pppoatm_pop(), it's safe to clear the BLOCKED bit here because
+ * the wakeup *can't* race with pppoatm_send(). They both hold the PPP
+ * channel's ->downl lock. And the potential race with *setting* it,
+ * which leads to the double-check dance in pppoatm_may_send(), doesn't
+ * exist here. In the sock_owned_by_user() case in pppoatm_send(), we
+ * set the BLOCKED bit while the socket is still locked. We know that
+ * ->release_cb() can't be called until that's done.
+ */
+ if (test_and_clear_bit(BLOCKED, &pvcc->blocked))
+ tasklet_schedule(&pvcc->wakeup_tasklet);
if (pvcc->old_release_cb)
pvcc->old_release_cb(atmvcc);
}
@@ -292,8 +302,15 @@ static int pppoatm_send(struct ppp_channel *chan, struct sk_buff *skb)
vcc = ATM_SKB(skb)->vcc;
bh_lock_sock(sk_atm(vcc));
- if (sock_owned_by_user(sk_atm(vcc)))
+ if (sock_owned_by_user(sk_atm(vcc))) {
+ /*
+ * Needs to happen (and be flushed, hence test_and_) before we unlock
+ * the socket. It needs to be seen by the time our ->release_cb gets
+ * called.
+ */
+ test_and_set_bit(BLOCKED, &pvcc->blocked);
goto nospace;
+ }
if (test_bit(ATM_VF_RELEASED, &vcc->flags) ||
test_bit(ATM_VF_CLOSE, &vcc->flags) ||
!test_bit(ATM_VF_READY, &vcc->flags)) {

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