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Date: Fri, 16 Jan 2015 16:46:39 -0800 From: Darren Hart <dvhart@...ux.intel.com> To: "Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>, Thomas Gleixner <tglx@...utronix.de> CC: Carlos O'Donell <carlos@...hat.com>, Ingo Molnar <mingo@...e.hu>, Jakub Jelinek <jakub@...hat.com>, "linux-man@...r.kernel.org" <linux-man@...r.kernel.org>, lkml <linux-kernel@...r.kernel.org>, Davidlohr Bueso <davidlohr.bueso@...com>, Arnd Bergmann <arnd@...db.de>, Steven Rostedt <rostedt@...dmis.org>, Peter Zijlstra <peterz@...radead.org>, Linux API <linux-api@...r.kernel.org>, Torvald Riegel <triegel@...hat.com>, Roland McGrath <roland@...hat.com>, Darren Hart <dvhart@...radead.org>, Anton Blanchard <anton@...ba.org>, Petr Baudis <pasky@...e.cz>, Eric Dumazet <edumazet@...gle.com>, bill o gallmeister <bgallmeister@...il.com>, Jan Kiszka <jan.kiszka@...mens.com>, Daniel Wagner <wagi@...om.org>, Rich Felker <dalias@...c.org> Subject: Re: futex(2) man page update help request On 1/16/15, 12:54 PM, "Michael Kerrisk (man-pages)" <mtk.manpages@...il.com> wrote: >On 01/16/2015 04:20 PM, Thomas Gleixner wrote: >> On Fri, 16 Jan 2015, Michael Kerrisk (man-pages) wrote: >> >>> Hello Thomas, >>> >>> On 01/15/2015 11:23 PM, Thomas Gleixner wrote: >>>> On Thu, 15 Jan 2015, Michael Kerrisk (man-pages) wrote: >>>>>> [EINVAL] uaddr equal uaddr2. Requeue to same futex. >>>>> >>>>> ??? I added this, but does this error not occur only for PI requeues? >>>> >>>> It's equally wrong for normal futexes. And its actually the same code >>>> checking for this for all variants. >>> >>> I don't understand "equally wrong" in your reply, I'm sorry. Do you >>> mean: >>> >>> a) This error text should be there for both normal and PI requeues >> >> It is there for both. The requeue code has that check independent of >> the requeue type (normal/pi). It never makes sense to requeue >> something to itself whether normal or pi futex. We added this for PI, >> because there it is harmful, but we did not special case it. So normal >> futexes get the same treatment. > >Hello Thomas, > >Color me stupid, but I can't see this in futex_requeue(). Where is that >check that is "independent of the requeue type (normal/pi)"? > >When I look through futex_requeue(), all the likely looking sources >of EINVAL are governed by a check on the 'requeue_pi' argument. Right, in the non-PI case, I believe there are valid use cases: move to the back of the FIFO, for example (OK, maybe the only example?). Both tests ensuring uaddr1 != uaddr2 are under the requeue_pi conditional block. The second compares the keys in case they are not FUTEX_PRIVATE (uaddrs would be different, but still the same backing store). Thomas, am I missing a test for this someplace else? -- Darren Hart Intel Open Source Technology Center -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.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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