From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <4739E74A.1080705@domain.hid> Date: Tue, 13 Nov 2007 19:04:58 +0100 From: Philippe Gerum MIME-Version: 1.0 References: <2ff1a98a0711130556j58141e80yc0bca6b574fad7e9@domain.hid> <4739B1DC.4030705@domain.hid> <2ff1a98a0711130634x552683c4ib1c420a859a4d665@domain.hid> <4739DA74.7040409@domain.hid> <2ff1a98a0711130924k3a81a5b8jf11982437308876e@domain.hid> <4739E29B.3080908@domain.hid> In-Reply-To: <4739E29B.3080908@domain.hid> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: Philippe Gerum Subject: Re: [Xenomai-core] local_irq_save/local_irq_restore in real-time interrupt handler and slab corruption. Reply-To: rpm@xenomai.org List-Id: "Xenomai life and development \(bug reports, patches, discussions\)" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: rpm@xenomai.org Cc: xenomai-core Philippe Gerum wrote: > Gilles Chanteperdrix wrote: >> On Nov 13, 2007 6:10 PM, Philippe Gerum wrote: >>> Gilles Chanteperdrix wrote: >>>> On Nov 13, 2007 3:17 PM, Jan Kiszka wrote: >>>>> Gilles Chanteperdrix wrote: >>>>>> Hi, >>>>>> >>>>>> I am chasing a slab corruption bug which happens on a Xenomai+RTnet >>>>>> enabled box under heavy non real-time network load (which passes >>>>>> through rtnet and rtmac_vnic to Linux which does NAT and resend it to >>>>>> another rtmac_vnic). When reading some I-pipe tracer traces, I >>>>>> remarked that I forgot to replace a local_irq_save/local_irq_restore >>>>>> with local_irq_save_hw/local_irq_restore_hw in a real-time interrupt >>>>>> handler. I fixed this bug, and the slab corruption seems to be gone. >>>>> Hope you mean rtdm_lock_irqsave/irqrestore instead. Otherwise Xenomai's >>>>> domain state would not be updated appropriately - which is at least unclean. >>>> It is some low level secondary timer handling code, there is no rtdm >>>> involved. The code protected by the interrupt masking routines is one >>>> or two inline assembly instructions. >>>> >>>>> BTW, CONFIG_IPIPE_DEBUG_CONTEXT should have caught this bug as well. >>>> I am using an old I-pipe pacth without CONFIG_IPIPE_DEBUG_CONTEXT. >>>> I-pipe patch and Xenomai update is scheduled for when RT applications >>>> and drivers porting will be finished. >>>> >>>> Besides the BUG_ON(!ipipe_root_domain_p) in ipipe_restore_root and >>>> ipipe_unstall_root are unconditional. >>>> >>> What bothers me, is that even looking at the old 1.3 series here and on, >>> the code should exhibit a call chain like >>> local_irq_restore -> raw_local_irq_restore() -> __ipipe_restore_root -> >>> __ipipe_unstall_root -> __ipipe_sync_stage, without touching the current >>> domain pointer, which is ok, since well, it has to be right in the first >>> place. If we were running over a real-time handler, then I assume the >>> Xenomai domain was active. So BUG_ON() should have triggered if present >>> in __ipipe_unstall_root. >> I am using an I-pipe arm 1.5-04 (now that I have done cat >> /proc/ipipe/version, I really feel ashamed). And it has no BUG_ON in >> __ipipe_unstall_root or __ipipe_restore_root. I promise, one day, I >> will switch to Xenomai 2.4. >> >>> Additionally, calling __ipipe_sync_pipeline() would sync the current >>> stage, i.e. Xenomai, and run the real-time ISRs, not the Linux handlers. >>> >>> Mm, ok, in short: I have no clue. >> The system runs stably, so I have to assume that calling >> local_irq_restore in a real-time interrupt handler can cause slab >> corruption. Strange. >> > > I guess this is likely not on your critical path, but when time allows, > I'd be interested to know whether such bug still occurs when using a > purely kernel-only tasking, assuming that you currently see this bug > with userland tasks. Basically, I wonder if migrating shadows between > both domains would not reveal the bug, since your real-time handler > starts being preemptible by hw IRQs as soon as it returns from > __ipipe_unstall_root, which forces local_irq_enable_hw(). > Well, the 1.5 series still has a deep log, so you would also have to make sure that no IRQ is pending in the pipeline. -- Philippe.