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SubjectRe: [PATCH] Export current_is_keventd() for libphy
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Date
 > a) Ban the calling of flush_scheduled_work() from under rtnl_lock(). 
> Sounds hard.

Unfortunate if this is happening a lot. It seems like the most
sensible fix -- flush_scheduled_work() is in effect calling into
an unknown and changeable in the future set of functions (since it
waits for them to finish), and it seems error-prone to hold a lock
across such a call.

> This will almost work, as long as it's done in workqueue.c with
> appropriate locking. The bug occurs when some other CPU is running
> phy_change() right now - we'll end up freeing data which that CPU is
> presently playing with.
>
> But perhaps we can take care of this within workqueue.c. We need a
> cancel function which will cancel the work and, if its callback is
> presently executing it will block until that execution has completed.

I may be misunderstanding you, but this seems to deadlock in exactly
the same way: if someone calls this cancel routine holding rtnl_lock,
and the work function that will also take rtnl_lock has just started,
it will get stuck when the work function tries to take rtnl_lock.

- R.
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