Messages in this thread | | | Date | Thu, 16 Feb 2006 20:06:48 +0100 (MET) | From | Esben Nielsen <> | Subject | Re: [patch 0/6] lightweight robust futexes: -V3 - Why in userspace? |
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I just jump into a thread somewhere to ask my question :-)
Why does the list have to be in userspace?
As I see it there can only be a problem when some thread has done FUTEX_WAIT and is blocked. If no task is blocked (or on it's way to being blocked) there is no problem.
The solution I could imagine was the FUTEX_WAIT operation adds the waiting task to a list of waiters attached to the mutex owner's task_t (which is known by it's pid in the userspace flag) just before calling schedule(). This list needs to be protected by a spinlock, ofcourse. When a task dies it can wake up the waiters on it's list without relying on the userspace.
What race conditions have I missed?
Esben
On Thu, 16 Feb 2006, Daniel Walker wrote:
> On Thu, 2006-02-16 at 18:24 +0100, Ingo Molnar wrote: > > * Daniel Walker <dwalker@mvista.com> wrote: > > > > > Another thing I noticed was that futex_offset on the surface looks > > > like a malicious users dream variable .. [...] > > > > i have no idea what you mean by that - could you explain whatever threat > > you have in mind, in more detail? > > As I said, "on the surface" you could manipulate the futex_offset to > access memory unrelated to the futex structure . That's all I'm > referring too .. > > Daniel > > - > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ >
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