#1903: Channel switch on active interface in master mode causes hard lockup
--------------------------------------+-------------------------------------
Reporter: sjen...@versanet.de | Owner: proski
Type: defect | Status: assigned
Priority: blocker | Milestone: version 0.9.4.1
Component: madwifi: driver | Version: v0.9.4
Resolution: | Keywords: master mode ap deadlock
freeze channel
Patch_attached: 0 | Pending: 0
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Comment (by proski):
The fundamental problem lies in net80211/ieee80211_node.c:
{{{
/*
* XXX: may need to lock out the following race. we dectestref
* and determine it's time to free the node. between the if()
* and lock, we take an rx intr to receive a frame from this
* node. the rx path (tasklet or intr) bumps this node's
* refcnt and xmits a response frame. eventually that
response
* will get reaped, and the reaping code will attempt to use
* the node. the code below will delete the node prior
* to the reap and we could get a crash.
*
* as a stopgap before delving deeper, lock intrs to
* prevent this case.
*/
IEEE80211_LOCK_IRQ(ic);
}}}
IEEE80211_LOCK_IRQ is spin_lock_irqsave(). It doesn't lock all interrupts
on SMP systems. It only locks interrupts on the current CPU. Other CPUs
will still run. If any of them needs to acquire that spinlock, the CPU
will stop and wait. spin_lock_irqsave() is a wrong function for the job
it's supposed to do.
--
Ticket URL: <https://madwifi-project.org/ticket/1903#comment:27>
madwifi-project.org <http://madwifi-project.org/>
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