svn commit: r192535 - head/sys/kern

M. Warner Losh imp at bsdimp.com
Thu May 21 15:43:59 UTC 2009


In message: <alpine.BSF.2.00.0905211610140.18790 at fledge.watson.org>
            Robert Watson <rwatson at FreeBSD.org> writes:
: 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.

devctl_notify() has expanded well beyond its original needs.  Having
an extra case for sleeping is the wrong way to solve this problem.
Really.  We're adding hacks on hacks on hacks here and we need to step
back and think.

I specifically didn't put in CDEV notifications into devd when I
originally did it because one can get the same notification via
kevents on /dev.  Maybe the right answer is to remove this stuff
entirely and update devd to do that instead?  It isn't a lot of code,
and should provide equivalent functionality without needing to change
the rules of the game when it comes to destroy_dev().  Especially this
close to the code slush...

Comments?

Warner


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