svn commit: r192535 - head/sys/kern

Robert Watson rwatson at
Thu May 21 15:11:06 UTC 2009

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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