I get an awfully verbose lockdep warning when I bring up ipoib devices
and wanted to make sure it didn't go unreported. I've put it up at the
following URL:
http://oss.oracle.com/~zab/ipoib-multicast-lockdep-warning.txt
I looked into it a bit and it seems to be on to something. There might
be a AB, BC, CA ordering deadlock.
AB:
priv->lock is held while acquiring query_idr.lock
ipoib_mcast_send()
spin_lock(&priv->lock);
ipoib_mcast_sendonly_join()
ib_sa_mcmember_rec_query()
send_mad()
idr_pre_get(&query_idr)
spin_lock(&idp->lock);
BC:
query_idr.lock is taken with interrupts enabled and so is implicitly
ordered before dev->_xmit_lock which is taken in interrupt context.
ipoib_mcast_join_task()
ipoib_mcast_join()
ib_sa_mcmember_rec_query()
send_mad()
idr_pre_get(&query_idr)
spin_lock(&idp->lock)
CA:
dev->_xmit_lock is held while acquiring priv->lock. This triggers the
lockdep warning that adding the dep between dev->_xmit_lock and
priv->lock connects a soft-irq-safe lock to a soft-irq-unsafe one.
ipoib_mcast_restart_task()
local_irq_save(flags);
netif_tx_lock(dev)
spin_lock(&dev->_xmit_lock);
spin_lock(&priv->lock);
I can imagine all sorts of potential fixes (block ints when calling idr?
reorder acquiry in ipoib_mcast_restart_task()?) but I'm operating on a
partial view of the paths here so I wasn't comfortable suggesting a fix.
I wouldn't be surprised to hear that there are circumstances that both
lockdep and I don't know about that stop this from being a problem :).
In any case, it'd be fantastic if someone who knows this code could sit
down with lockdep and some ipoib regression suite to shake out lockdep's
complaints.
- z
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