From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <4B59E87F.80108@domain.hid> Date: Fri, 22 Jan 2010 19:03:43 +0100 From: Jan Kiszka MIME-Version: 1.0 References: <4B59D952.30202@domain.hid> <1264181859.2350.152.camel@domain.hid> <4B59E2D4.5040004@domain.hid> <4B59E33E.1040203@domain.hid> <1264182738.2350.158.camel@domain.hid> In-Reply-To: <1264182738.2350.158.camel@domain.hid> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Subject: Re: [Xenomai-core] Domain switch during page fault handling List-Id: Xenomai life and development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Philippe Gerum Cc: "Mauerer, Wolfgang" , xenomai-core Philippe Gerum wrote: > On Fri, 2010-01-22 at 18:41 +0100, Jan Kiszka wrote: >> Gilles Chanteperdrix wrote: >>> Philippe Gerum wrote: >>>> On Fri, 2010-01-22 at 17:58 +0100, Jan Kiszka wrote: >>>>> Hi guys, >>>>> >>>>> we are currently trying to catch an ugly Linux pipeline state corruption >>>>> on x86-64. >>>>> >>>>> Conceptual question: If a Xenomai task causes a fault, we enter >>>>> ipipe_trap_notify over the primary domain and leave it over the root >>>>> domain, right? Now, if the root domain happened to be stalled when the >>>>> exception happened, where should it normally be unstalled again, >>>>> *for_that_task*? Our problem is that we generate a code path where this >>>>> does not happen. >>>> xnhadow_relax -> ipipe_reenter_root -> finish_task_switch -> >>>> finish_lock_switch -> unstall >>>> >>>> Since xnshadow_relax is called on behalf the event dispatcher, we should >>>> expect it to return with the root domain unstalled after a domain >>>> downgrade, from primary to root. >>> Ok, but what about local_irq_restore_nosync at the end of the function ? >>> >> That is, IMO, our problem: It replays the root state on fault entry, but >> that one is totally unrelated to the (Xenomai) task that caused the fault. > > The code seems fishy. Try restoring only when the incoming domain was > the root one. Indeed. > Something like this? diff --git a/arch/x86/kernel/ipipe.c b/arch/x86/kernel/ipipe.c index 4442d96..0558ea3 100644 --- a/arch/x86/kernel/ipipe.c +++ b/arch/x86/kernel/ipipe.c @@ -702,19 +702,21 @@ static int __ipipe_xlate_signo[] = { int __ipipe_handle_exception(struct pt_regs *regs, long error_code, int vector) { + bool restore_flags = false; unsigned long flags; - /* Pick up the root domain state of the interrupted context. */ - local_save_flags(flags); + if (ipipe_root_domain_p && irqs_disabled_hw()) { + /* Pick up the root domain state of the interrupted context. */ + local_save_flags(flags); - if (ipipe_root_domain_p) { /* * Replicate hw interrupt state into the virtual mask before * calling the I-pipe event handler over the root domain. Also * required later when calling the Linux exception handler. */ - if (irqs_disabled_hw()) - local_irq_disable(); + local_irq_disable(); + + restore_flags = true; } #ifdef CONFIG_KGDB /* catch exception KGDB is interested in over non-root domains */ @@ -725,7 +727,8 @@ int __ipipe_handle_exception(struct pt_regs *regs, long error_code, int vector) #endif /* CONFIG_KGDB */ if (unlikely(ipipe_trap_notify(vector, regs))) { - local_irq_restore_nosync(flags); + if (restore_flags) + local_irq_restore_nosync(flags); return 1; } @@ -770,7 +773,8 @@ int __ipipe_handle_exception(struct pt_regs *regs, long error_code, int vector) * Relevant for 64-bit: Restore root domain state as the low-level * return code will not align it to regs.flags. */ - local_irq_restore_nosync(flags); + if (restore_flags) + local_irq_restore_nosync(flags); return 0; } We are currently not able to test this on the system that triggers it, but we'll do so tomorrow (yeah...). Jan -- Siemens AG, Corporate Technology, CT T DE IT 1 Corporate Competence Center Embedded Linux