On Mon, Jun 22, 2020 at 12:24:01PM +0200, Dominique Martinet wrote: > Christian Brauner wrote on Mon, Jun 22, 2020: > > On Mon, Jun 22, 2020 at 08:25:28AM +0200, Oleg Nesterov wrote: > >> current->sighand is stable and can't go away. Unless "current" is exiting > >> and > >> has already passed exit_notify(). So I don't think net/9p needs this > >> helper. > > > > From what I can gather from the thread (cf. [1]) that is linked in the > > commit message the main motivation for all of this is sparse not being > > happy and not some bug. (Maybe I'm not seeing something though.) > > > > The patch itself linked here doesn't seem to buy anything. I agree with > > Oleg. Afaict, lock_task_sighand() would only be needed here if the task > > wouldn't be current. So maybe it should just be dropped from the series. > > Sure. I honestly have no idea on what guarantees we have from the task > being current here as opposed to any other task -- I guess that another > thread calling exit for exemple would have to wait?
When a thread in a non-trivial thread-group (sorry for the math reference :)) execs it'll unshare its struct sighand. The new struct sighand will be assigned using rcu_assign_pointer() so afaik (Paul or Oleg can yell at me if I'm talking nonsense) any prior callers will see the prior sighand value. > What about the possibility of sighand being null that the function does > check, is that impossible for current as well? See above, I think that's impossible. > > > Honestly not a part of the code I'm much familiar with, this all > predates my involvement with 9p by a fair bit... We can't be experts in everything. :) Christian