On Thu, Dec 08, 2011 at 12:50:55PM -0800, Tejun Heo wrote: > (Note for Linus at the bottom) > > threadgroup_lock() protected only protected against new addition to > the threadgroup, which was inherently somewhat incomplete and > problematic for its only user cgroup. On-going migration could race > against exec and exit leading to interesting problems - the symmetry > between various attach methods, task exiting during method execution, > ->exit() racing against attach methods, migrating task switching basic > properties during exec and so on. > > This patch extends threadgroup_lock() such that it protects against > all three threadgroup altering operations - fork, exit and exec. For > exit, threadgroup_change_begin/end() calls are added to exit_signals > around assertion of PF_EXITING. For exec, threadgroup_[un]lock() are > updated to also grab and release cred_guard_mutex. > > With this change, threadgroup_lock() guarantees that the target > threadgroup will remain stable - no new task will be added, no new > PF_EXITING will be set and exec won't happen. > > The next patch will update cgroup so that it can take full advantage > of this change. > > -v2: beefed up comment as suggested by Frederic. > > -v3: narrowed scope of protection in exit path as suggested by > Frederic. > > Signed-off-by: Tejun Heo <tj@xxxxxxxxxx> > Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> > Acked-by: Li Zefan <lizf@xxxxxxxxxxxxxx> > Cc: Oleg Nesterov <oleg@xxxxxxxxxx> > Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> > Cc: Paul Menage <paul@xxxxxxxxxxxxxx> > Cc: Frederic Weisbecker <fweisbec@xxxxxxxxx> > Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> > --- > Okay, narrowed exit path protection down to setting of PF_EXITING > itself. ->exit() on dangling tasks is a bit weird but I don't think > it's too bad. Frederic, are you okay with this version? Yeah that new scheme that only protects PF_EXITING may look a bit strange. But I think we are fine. With rcu list traversal, it should be safe even if a group member is concurrently dropped from the list (in that case all we check if its PF_EXITING then we give up). And we may have a concurrent ->exit() but that should be fine too. Thanks! Acked-by: Frederic Weisbecker <fweisbec@xxxxxxxxx> > > Linus, if Frederic is okay with it, I'm gonna rebase the series on top > of freezer changes in pm tree to avoid conflicts in cgroup_freezer, > which sits between cgroup and freezer, both of which are going through > non-trivial changes, push the branch to linux-next and put pending > cgroup patches on top. Please scream if you're mighty unhappy with it > or have a better idea. > > Thank you. _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/linux-pm
