| Message ID | dc3e7811-e3f8-1cf9-d556-1ac57288daa5@suse.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Fri, 7 Jul 2017, Juergen Gross wrote: > Commit bf22ff45bed664aefb5c4e43029057a199b7070c ("genirq: Avoid > unnecessary low level irq function calls") breaks Xen guest > save/restore handling. > > The main problem are the PV devices using Xen event channels as > interrupt sources which are represented as an "irq chip" in the kernel. > When saving the guest the event channels are masked internally. At > restore time event channels are re-established and unmasked via > irq_startup(). Unfortunately above commit will let the unmask operation > be a nop as the irq handling doesn't know about the masking done before. Rightfully so. Making assumptions about the inner workings of core code is always wrong. > I have a patch repairing the issue, but I'm not sure if this way to do > it would be accepted. I have exported mask_irq() and I'm doing the > masking now through this function. Would the attached patch be > acceptable? Or is there a better way to solve the problem? Without looking at the patch (too lazy to fiddle with attachments right now), this is definitely wrong. I'll have a look later tonight. Thanks, tglx
On 07/07/17 18:41, Thomas Gleixner wrote: > On Fri, 7 Jul 2017, Juergen Gross wrote: > >> Commit bf22ff45bed664aefb5c4e43029057a199b7070c ("genirq: Avoid >> unnecessary low level irq function calls") breaks Xen guest >> save/restore handling. >> >> The main problem are the PV devices using Xen event channels as >> interrupt sources which are represented as an "irq chip" in the kernel. >> When saving the guest the event channels are masked internally. At >> restore time event channels are re-established and unmasked via >> irq_startup(). Unfortunately above commit will let the unmask operation >> be a nop as the irq handling doesn't know about the masking done before. > > Rightfully so. Making assumptions about the inner workings of core code is > always wrong. That was my thought, too. :-) >> I have a patch repairing the issue, but I'm not sure if this way to do >> it would be accepted. I have exported mask_irq() and I'm doing the >> masking now through this function. Would the attached patch be >> acceptable? Or is there a better way to solve the problem? > > Without looking at the patch (too lazy to fiddle with attachments right > now), this is definitely wrong. I'll have a look later tonight. Thank you very much Juergen
On 07/07/17 15:51, Juergen Gross wrote: > Commit bf22ff45bed664aefb5c4e43029057a199b7070c ("genirq: Avoid > unnecessary low level irq function calls") breaks Xen guest > save/restore handling. > > The main problem are the PV devices using Xen event channels as > interrupt sources which are represented as an "irq chip" in the kernel. > When saving the guest the event channels are masked internally. At > restore time event channels are re-established and unmasked via > irq_startup(). Unfortunately above commit will let the unmask operation > be a nop as the irq handling doesn't know about the masking done before. > > I have a patch repairing the issue, but I'm not sure if this way to do > it would be accepted. I have exported mask_irq() and I'm doing the > masking now through this function. Would the attached patch be > acceptable? Or is there a better way to solve the problem? The correct API to prevent an interrupt from firing would be disable_irq(), which is much more straightforward and is readily exported. I'm unsure of what the expected flow is though, so there might be some more fixes to be made in your code. Thanks, M.
On Fri, 7 Jul 2017, Thomas Gleixner wrote: > On Fri, 7 Jul 2017, Juergen Gross wrote: > > > Commit bf22ff45bed664aefb5c4e43029057a199b7070c ("genirq: Avoid > > unnecessary low level irq function calls") breaks Xen guest > > save/restore handling. > > > > The main problem are the PV devices using Xen event channels as > > interrupt sources which are represented as an "irq chip" in the kernel. > > When saving the guest the event channels are masked internally. At > > restore time event channels are re-established and unmasked via > > irq_startup(). And how exactly gets irq_startup() invoked on those event channels? > > I have a patch repairing the issue, but I'm not sure if this way to do > > it would be accepted. I have exported mask_irq() and I'm doing the > > masking now through this function. Would the attached patch be > > acceptable? Or is there a better way to solve the problem? > > Without looking at the patch (too lazy to fiddle with attachments right > now), this is definitely wrong. I'll have a look later tonight. Not that I'm surprised, but that patch is exactly what I expected. Export a random function, which helps to paper over the real problem and run away. These functions are internal for a reason and we worked hard on making people understand that fiddling with the internals of interrupts is a NONO. If there are special requirements for a good reason, then we create proper interfaces and infrastructure, if there is no good reason, then the problematic code needs to be fixed. There is no exception for XEN. Can you please explain how that save/restore stuff works and which functions are involved? Thanks, tglx
On 07/07/17 19:11, Thomas Gleixner wrote: > On Fri, 7 Jul 2017, Thomas Gleixner wrote: > >> On Fri, 7 Jul 2017, Juergen Gross wrote: >> >>> Commit bf22ff45bed664aefb5c4e43029057a199b7070c ("genirq: Avoid >>> unnecessary low level irq function calls") breaks Xen guest >>> save/restore handling. >>> >>> The main problem are the PV devices using Xen event channels as >>> interrupt sources which are represented as an "irq chip" in the kernel. >>> When saving the guest the event channels are masked internally. At >>> restore time event channels are re-established and unmasked via >>> irq_startup(). > > And how exactly gets irq_startup() invoked on those event channels? [ 30.791879] Call Trace: [ 30.791883] ? irq_get_irq_data+0xe/0x20 [ 30.791886] enable_dynirq+0x23/0x30 [ 30.791888] unmask_irq.part.33+0x26/0x40 [ 30.791890] irq_enable+0x65/0x70 [ 30.791891] irq_startup+0x3c/0x110 [ 30.791893] __enable_irq+0x37/0x60 [ 30.791895] resume_irqs+0xbe/0xe0 [ 30.791897] irq_pm_syscore_resume+0x13/0x20 [ 30.791900] syscore_resume+0x50/0x1b0 [ 30.791902] xen_suspend+0x76/0x140 > >>> I have a patch repairing the issue, but I'm not sure if this way to do >>> it would be accepted. I have exported mask_irq() and I'm doing the >>> masking now through this function. Would the attached patch be >>> acceptable? Or is there a better way to solve the problem? >> >> Without looking at the patch (too lazy to fiddle with attachments right >> now), this is definitely wrong. I'll have a look later tonight. > > Not that I'm surprised, but that patch is exactly what I expected. Export a > random function, which helps to paper over the real problem and run away. > These functions are internal for a reason and we worked hard on making > people understand that fiddling with the internals of interrupts is a > NONO. If there are special requirements for a good reason, then we create > proper interfaces and infrastructure, if there is no good reason, then the > problematic code needs to be fixed. There is no exception for XEN. I'm absolutely on your side here. That was the reason I didn't send the patch right away, but asked how to solve my issue in a way which isn't "quick and dirty". The patch was just the easiest way to explain what should be the result of the proper solution. > Can you please explain how that save/restore stuff works and which > functions are involved? It is based on suspend/resume framework. The main work to be done additionally is to disconnect from the pv-backends at save time and connect to the pv-backends again at restore time. The main function triggering all that is xen_suspend() (as seen in above backtrace). Juergen
diff --git a/drivers/xen/events/events_base.c b/drivers/xen/events/events_base.c index 2e567d8433b3..79e82534a3c3 100644 --- a/drivers/xen/events/events_base.c +++ b/drivers/xen/events/events_base.c @@ -346,9 +346,17 @@ static void bind_evtchn_to_cpu(unsigned int chn, unsigned int cpu) static void xen_evtchn_mask_all(void) { unsigned int evtchn; + int irq; + struct irq_desc *desc; - for (evtchn = 0; evtchn < xen_evtchn_nr_channels(); evtchn++) - mask_evtchn(evtchn); + for (evtchn = 0; evtchn < xen_evtchn_nr_channels(); evtchn++) { + irq = get_evtchn_to_irq(evtchn); + desc = irq_to_desc(irq); + if (desc) + mask_irq(desc); + else + mask_evtchn(evtchn); + } } /** diff --git a/include/linux/irq.h b/include/linux/irq.h index 00db35b61e9e..4b6ab670639a 100644 --- a/include/linux/irq.h +++ b/include/linux/irq.h @@ -509,6 +509,7 @@ extern int setup_irq(unsigned int irq, struct irqaction *new); extern void remove_irq(unsigned int irq, struct irqaction *act); extern int setup_percpu_irq(unsigned int irq, struct irqaction *new); extern void remove_percpu_irq(unsigned int irq, struct irqaction *act); +extern void mask_irq(struct irq_desc *desc); extern void irq_cpu_online(void); extern void irq_cpu_offline(void); diff --git a/kernel/irq/chip.c b/kernel/irq/chip.c index 2e30d925a40d..7e25a1ad2857 100644 --- a/kernel/irq/chip.c +++ b/kernel/irq/chip.c @@ -408,6 +408,7 @@ void mask_irq(struct irq_desc *desc) irq_state_set_masked(desc); } } +EXPORT_SYMBOL_GPL(mask_irq); void unmask_irq(struct irq_desc *desc) { diff --git a/kernel/irq/internals.h b/kernel/irq/internals.h index 9da14d125df4..5e2bc4d799af 100644 --- a/kernel/irq/internals.h +++ b/kernel/irq/internals.h @@ -81,7 +81,6 @@ extern void irq_enable(struct irq_desc *desc); extern void irq_disable(struct irq_desc *desc); extern void irq_percpu_enable(struct irq_desc *desc, unsigned int cpu); extern void irq_percpu_disable(struct irq_desc *desc, unsigned int cpu); -extern void mask_irq(struct irq_desc *desc); extern void unmask_irq(struct irq_desc *desc); extern void unmask_threaded_irq(struct irq_desc *desc);
Commit bf22ff45bed664aefb5c4e43029057a199b7070c ("genirq: Avoid unnecessary low level irq function calls") breaks Xen guest save/restore handling. The main problem are the PV devices using Xen event channels as interrupt sources which are represented as an "irq chip" in the kernel. When saving the guest the event channels are masked internally. At restore time event channels are re-established and unmasked via irq_startup(). Unfortunately above commit will let the unmask operation be a nop as the irq handling doesn't know about the masking done before. I have a patch repairing the issue, but I'm not sure if this way to do it would be accepted. I have exported mask_irq() and I'm doing the masking now through this function. Would the attached patch be acceptable? Or is there a better way to solve the problem? Juergen