Messages in this thread | | | Date | Tue, 10 Dec 2013 18:01:16 -0500 | From | Dave Jones <> | Subject | Re: process 'stuck' at exit. |
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On Tue, Dec 10, 2013 at 02:58:19PM -0800, Darren Hart wrote: > On Tue, 2013-12-10 at 14:48 -0800, Linus Torvalds wrote: > > On Tue, Dec 10, 2013 at 2:42 PM, Thomas Gleixner <tglx@linutronix.de> wrote: > > > > > > And yes, I remember that we do not do an extra check for the fshared > > > case, because get_user_pages_fast() should do it for us already. If > > > not we are fubared not only in the futex code. > > > > Yeah. It turns out we do do the access check indirectly - by looking > > at the PAGE_USER bit, even if we don't necessarily check the actual > > limits. So get_user_pages_fast() is fine. > > > > > But there is a subtle detail: > > > > Yup, see my email from ten minutes ago, we found the same thing. And > > that would seem to explain the endless loop, and also the timing > > (since Dave mentions he started doing large-pages lately). > > > > So I think the "__get_user_pages_fast(address, 1, !ro, &page)" thing > > should work. > > > > Dave, can you re-create that trinity run and test that patch? I think > > we've got this, but it might be nice to leave the hung machine up and > > running until it's verified.. Although I don't really see what else we > > could need or get out of it, so.. > > Would it be possible to limit the options to only pass FUTEX_CMP_REQUEUE > and a read-only uaddr? That should improve confidence when it doesn't > fail :-)
easy enough to hack into the code yeah. A bit complicated to come up with a sensible grammar for a command line parser for such cases sadly.
I'll give the patch a try after dinner.
Dave
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