On Wed, Oct 31, 2012 at 10:16:18AM +0000, David Woodhouse wrote: > > Does this break the pvcc->blocked handling that coordinates with > pppoatm_pop()? > > If we have one packet in flight, so pppoatm_may_send() permits a new one > to be queued... but they're *large* packets to sk_wmem_alloc doesn't > permit it. Immediately after the check, pppoatm_pop() runs and leaves > the queue empty. We return zero, blocking the queue??? which never gets > woken because we didn't set the BLOCKED flag and thus the tasklet never > runs. > > In fact, I think we need the BLOCKED handling for the > sock_owned_by_user() case too? When the VCC is actually closed, I > suppose that's not recoverable and we don't care about waking the queue > anyway? But any time we end up returning zero from pppoatm_send(), we > *need* to ensure that a wakeup will happen in future unless the socket > is actually dead. >
Yes, original patch had also the same problem with sock_owned_by_user(), so I just incorrectly assumed that we can do "goto nospace" after pppoatm_may_send(), but ppooatm_may_send() must be the last test. So I just moved all other tests earlier and and now pppoatm_may_send() is also protected by ATM socket lock as you suggested earlier. Krzysiek -- >8 -- Subject: [PATCH] pppoatm: fix race condition with destroying of vcc The pppoatm_send() calls vcc->send() and now also checks for some vcc flags that indicate destroyed vcc without proper locking. The vcc_sendmsg() uses lock_sock(sk). This lock is used by vcc_release(), so vcc_destroy_socket() will not be called between check and during ->send(). The vcc_release_async() sets ATM_VF_CLOSE, but it should be safe to call ->send() after it, because vcc->dev->ops->close() is not called. The pppoatm_send() is called with BH disabled, so bh_lock_sock() should be used instead of lock_sock(). Signed-off-by: Krzysztof Mazur <[email protected]> --- net/atm/pppoatm.c | 27 +++++++++++++++++++-------- 1 file changed, 19 insertions(+), 8 deletions(-) diff --git a/net/atm/pppoatm.c b/net/atm/pppoatm.c index 0dcb5dc..eb76bd3 100644 --- a/net/atm/pppoatm.c +++ b/net/atm/pppoatm.c @@ -270,11 +270,22 @@ static int pppoatm_send(struct ppp_channel *chan, struct sk_buff *skb) { struct pppoatm_vcc *pvcc = chan_to_pvcc(chan); struct atm_vcc *vcc; + int ret; ATM_SKB(skb)->vcc = pvcc->atmvcc; pr_debug("(skb=0x%p, vcc=0x%p)\n", skb, pvcc->atmvcc); if (skb->data[0] == '\0' && (pvcc->flags & SC_COMP_PROT)) (void) skb_pull(skb, 1); + + vcc = ATM_SKB(skb)->vcc; + bh_lock_sock(sk_atm(vcc)); + if (sock_owned_by_user(sk_atm(vcc))) + goto nospace; + if (test_bit(ATM_VF_RELEASED, &vcc->flags) + || test_bit(ATM_VF_CLOSE, &vcc->flags) + || !test_bit(ATM_VF_READY, &vcc->flags)) + goto nospace; + switch (pvcc->encaps) { /* LLC encapsulation needed */ case e_llc: if (skb_headroom(skb) < LLC_LEN) { @@ -287,8 +298,10 @@ static int pppoatm_send(struct ppp_channel *chan, struct sk_buff *skb) } consume_skb(skb); skb = n; - if (skb == NULL) + if (skb == NULL) { + bh_unlock_sock(sk_atm(vcc)); return DROP_PACKET; + } } else if (!pppoatm_may_send(pvcc, skb->truesize)) goto nospace; memcpy(skb_push(skb, LLC_LEN), pppllc, LLC_LEN); @@ -298,24 +311,22 @@ static int pppoatm_send(struct ppp_channel *chan, struct sk_buff *skb) goto nospace; break; case e_autodetect: + bh_unlock_sock(sk_atm(vcc)); pr_debug("Trying to send without setting encaps!\n"); kfree_skb(skb); return 1; } - vcc = ATM_SKB(skb)->vcc; - if (test_bit(ATM_VF_RELEASED, &vcc->flags) - || test_bit(ATM_VF_CLOSE, &vcc->flags) - || !test_bit(ATM_VF_READY, &vcc->flags)) - goto nospace; - atomic_add(skb->truesize, &sk_atm(ATM_SKB(skb)->vcc)->sk_wmem_alloc); ATM_SKB(skb)->atm_options = ATM_SKB(skb)->vcc->atm_options; pr_debug("atm_skb(%p)->vcc(%p)->dev(%p)\n", skb, ATM_SKB(skb)->vcc, ATM_SKB(skb)->vcc->dev); - return ATM_SKB(skb)->vcc->send(ATM_SKB(skb)->vcc, skb) + ret = ATM_SKB(skb)->vcc->send(ATM_SKB(skb)->vcc, skb) ? DROP_PACKET : 1; + bh_unlock_sock(sk_atm(vcc)); + return ret; nospace: + bh_unlock_sock(sk_atm(vcc)); /* * We don't have space to send this SKB now, but we might have * already applied SC_COMP_PROT compression, so may need to undo -- 1.8.0.172.g62af90c -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
