On Wed, Sep 26, 2012 at 01:58:20PM -0600, Kenneth D. Merry wrote: > On Wed, Sep 26, 2012 at 21:45:41 +0200, Pawel Jakub Dawidek wrote: > > On Wed, Sep 26, 2012 at 01:21:17PM -0600, Kenneth D. Merry wrote: > > > On Wed, Sep 26, 2012 at 20:53:39 +0200, Pawel Jakub Dawidek wrote: > > > > On Wed, Sep 26, 2012 at 11:29:17AM -0600, Kenneth D. Merry wrote: > > > > > Here is what CAM needs at each step: > > > > > > > > > > 1. When a device goes away, we need a method to call from > > > > > daoninvalidate() > > > > > (or any other peripheral driver invalidate routine) with these > > > > > properties: > > > > > - It tells GEOM that the device has gone away, and starts the > > > > > process > > > > > of shutting down the device. (i.e. withers/orphans the > > > > > provider) > > > > > - It is callable from an interrupt context, with the SIM > > > > > (MTX_DEF) lock > > > > > held, so it can't sleep. > > > > > > > > Neither g_wither_provider() nor g_orphan_provider() require the topology > > > > lock. They only acquire the event lock, but it is regular mutex, so this > > > > is fine. Traversing geom's providers list looks like something that does > > > > need the topology lock, but maybe traversing is not needed at all. > > > > The reason for this change was a panic in iSCSI initiator where > > > > disk_gone() was called and provider was destroyed before g_wither_geom() > > > > returned. > > > > > > Ahh. How about using LIST_FOREACH_SAFE? Would that address the problem > > > at > > > hand? Are there any other races in there? > > > > It depends. If one geom can hold more than one provider then it might be > > racy, but from what I see there is always only one provider - there has > > to be only one, because disk_destroy() destroys it and struct disk > > represents always only one disk. If that's true then I see not reason to > > have a loop in there. I'd change it to: > > > > void > > disk_gone(struct disk *dp) > > { > > struct g_geom *gp; > > struct g_provider *pp; > > > > gp = dp->d_geom; > > if (gp != NULL) { > > pp = LIST_FIRST(&gp->provider); > > if (pp != NULL) > > g_wither_provider(pp, ENXIO); > > } > > } > > I would suggest doing LIST_FOREACH_SAFE() (with a comment explaining why) > instead. That way just in case someone adds another provider down the > road it will be handled properly. > > Otherwise we need a comment or KASSERT somewhere to explain that we depend > on there only being one provider, and things will break if there is more > than one.
I'm happy with adding KASSERT(), as I don't believe LIST_FOREACH_SAFE() will be safe there, as disk_gone() itself doesn't prevent the function to be called for two different disks, but one geom. LIST_FOREACH_SAFE() make it safe to remove only the current element. If any other elements is removed while we are traversing the list it will most likely panic. -- Pawel Jakub Dawidek http://www.wheelsystems.com FreeBSD committer http://www.FreeBSD.org Am I Evil? Yes, I Am! http://tupytaj.pl
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