On Mon, Apr 20, 2009 at 10:09:55PM +0000, Elad Efrat wrote: > Module Name: src > Committed By: elad > Date: Mon Apr 20 22:09:55 UTC 2009 > > Modified Files: > src/sys/kern: kern_verifiedexec.c > > Log Message: > PR/41251: YAMAMOTO Takashi: veriexec locking seems broken > > Part 1: Take the mountlist_lock before traversing the mount list.
Thanks for looking into this. However, there are some problems with your change: - mountlist_lock is a `leaf'. That is to say, it is never held for long and is never held for heavyweight operations. It also doesn't get intermixed with other locks. - For similar reasons, I suspect your change may introduce a lock ordering between mountlist_lock and other locks, which is undesirable. - The mountpoints you are looking at can be unmounted while you're examining them. The 'struct mount' won't disappear since you hold mountlist_lock, but see above. The solution to this is vfs_busy+vfs_unbusy. Have a grep in kern/ for uses of mountlist_lock. I think there are a few loops where all three are used together. Basically, they give you this: - vfs_busy() drops mountlist lock, but holds a reference to the mount for you, so it will not go away while you are inspecting it. - vfs_unbusy() reacquires mountlist_lock, and lets you continue traversing the list from where you left off. It also drpos the reference. - vfs_busy() locks the mount to prevent unmount().
