On Thu, 21 May 2009, John Baldwin wrote:
Move the M_WAITOK flag in notify() into an M_NOWAIT one in order to
match
the behaviour alredy present with the further malloc() call in
devctl_notify().
This fixes a bug in the CAM layer where the camisr handler finished to
call camperiphfree() (and subsequently destroy_dev() resulting in a new
dev notify) while the xpt lock is held.
This is wrong. You cannot call destroy_dev() while holding any mutex.
Taking this into account, it makes no sense to use M_NOWAIT in notify().
As long as devctl_notify() also calls M_NOWAIT and if not available skips
"silently" it just does the same thing, I think this approach is more
consistent.
It remains, though, the fact to fix CAM when calling destroy_dev(). Maybe
we should add a witness_warn() there?
I agree with kib, this should be reverted and CAM fixed instead. I also
agree that M_NOWAIT use should be limited where possible.
devctl_notify() probably needs to grow a sleepable flag, or perhaps we need
two variations, one that can sleep.
Robert N M Watson
Computer Laboratory
University of Cambridge
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