If a PCI System Error (SERR) is asserted it causes an NMI. If this NMI
occurs while the CPU is in printk() then Xen may deadlock as
pci_serr_error() calls console_force_unlock() which screws up the
console lock.
I don''t think removing the console_force_unlock() is sufficient as it
looks like printk() is unsafe to call from NMI context. We would like
keep the diagnostic. Does the following (untested) patch to defer the
printk() to a softirq look like a valid approach?
I also considered passing the NMI to dom0 (like other NMIs are) but I
couldn''t see how NMIs were handled in the current upstream pv-ops
kernels.
diff -r e2722b24dc09 xen/arch/x86/traps.c
--- a/xen/arch/x86/traps.c Thu Jan 26 17:43:31 2012 +0000
+++ b/xen/arch/x86/traps.c Tue Jan 31 16:28:45 2012 +0000
@@ -3173,6 +3173,11 @@ static void nmi_mce_softirq(void)
st->vcpu = NULL;
}
+static void pci_serr_softirq(void)
+{
+ printk("\n\nNMI - PCI system error (SERR)\n");
+}
+
void async_exception_cleanup(struct vcpu *curr)
{
int trap;
@@ -3259,10 +3264,11 @@ static void nmi_dom0_report(unsigned int
static void pci_serr_error(struct cpu_user_regs *regs)
{
- console_force_unlock();
- printk("\n\nNMI - PCI system error (SERR)\n");
-
outb((inb(0x61) & 0x0f) | 0x04, 0x61); /* clear-and-disable the PCI
SERR error line. */
+
+ /* Would like to print a diagnostic here but can''t call printk()
+ from NMI context -- raise a softirq instead. */
+ raise_softirq(PCI_SERR_SOFTIRQ);
}
static void io_check_error(struct cpu_user_regs *regs)
@@ -3563,6 +3569,7 @@ void __init trap_init(void)
cpu_init();
open_softirq(NMI_MCE_SOFTIRQ, nmi_mce_softirq);
+ open_softirq(PCI_SERR_SOFTIRQ, pci_serr_softirq);
}
long register_guest_nmi_callback(unsigned long address)
diff -r e2722b24dc09 xen/include/asm-x86/softirq.h
--- a/xen/include/asm-x86/softirq.h Thu Jan 26 17:43:31 2012 +0000
+++ b/xen/include/asm-x86/softirq.h Tue Jan 31 16:28:45 2012 +0000
@@ -6,6 +6,7 @@
#define VCPU_KICK_SOFTIRQ (NR_COMMON_SOFTIRQS + 2)
#define MACHINE_CHECK_SOFTIRQ (NR_COMMON_SOFTIRQS + 3)
-#define NR_ARCH_SOFTIRQS 4
+#define PCI_SERR_SOFTIRQ (NR_COMMON_SOFTIRQS + 4)
+#define NR_ARCH_SOFTIRQS 5
#endif /* __ASM_SOFTIRQ_H__ */
David
On 31/01/2012 16:37, "David Vrabel" <david.vrabel@citrix.com> wrote:> If a PCI System Error (SERR) is asserted it causes an NMI. If this NMI > occurs while the CPU is in printk() then Xen may deadlock as > pci_serr_error() calls console_force_unlock() which screws up the > console lock. > > I don''t think removing the console_force_unlock() is sufficient as it > looks like printk() is unsafe to call from NMI context. We would like > keep the diagnostic. Does the following (untested) patch to defer the > printk() to a softirq look like a valid approach?Yes, if the NMI is non-fatal then console_force_unlock() cannot be used. So your only other option is to defer the printk. -- Keir> I also considered passing the NMI to dom0 (like other NMIs are) but I > couldn''t see how NMIs were handled in the current upstream pv-ops kernels. > > diff -r e2722b24dc09 xen/arch/x86/traps.c > --- a/xen/arch/x86/traps.c Thu Jan 26 17:43:31 2012 +0000 > +++ b/xen/arch/x86/traps.c Tue Jan 31 16:28:45 2012 +0000 > @@ -3173,6 +3173,11 @@ static void nmi_mce_softirq(void) > st->vcpu = NULL; > } > > +static void pci_serr_softirq(void) > +{ > + printk("\n\nNMI - PCI system error (SERR)\n"); > +} > + > void async_exception_cleanup(struct vcpu *curr) > { > int trap; > @@ -3259,10 +3264,11 @@ static void nmi_dom0_report(unsigned int > > static void pci_serr_error(struct cpu_user_regs *regs) > { > - console_force_unlock(); > - printk("\n\nNMI - PCI system error (SERR)\n"); > - > outb((inb(0x61) & 0x0f) | 0x04, 0x61); /* clear-and-disable the PCI > SERR error line. */ > + > + /* Would like to print a diagnostic here but can''t call printk() > + from NMI context -- raise a softirq instead. */ > + raise_softirq(PCI_SERR_SOFTIRQ); > } > > static void io_check_error(struct cpu_user_regs *regs) > @@ -3563,6 +3569,7 @@ void __init trap_init(void) > cpu_init(); > > open_softirq(NMI_MCE_SOFTIRQ, nmi_mce_softirq); > + open_softirq(PCI_SERR_SOFTIRQ, pci_serr_softirq); > } > > long register_guest_nmi_callback(unsigned long address) > diff -r e2722b24dc09 xen/include/asm-x86/softirq.h > --- a/xen/include/asm-x86/softirq.h Thu Jan 26 17:43:31 2012 +0000 > +++ b/xen/include/asm-x86/softirq.h Tue Jan 31 16:28:45 2012 +0000 > @@ -6,6 +6,7 @@ > #define VCPU_KICK_SOFTIRQ (NR_COMMON_SOFTIRQS + 2) > > #define MACHINE_CHECK_SOFTIRQ (NR_COMMON_SOFTIRQS + 3) > -#define NR_ARCH_SOFTIRQS 4 > +#define PCI_SERR_SOFTIRQ (NR_COMMON_SOFTIRQS + 4) > +#define NR_ARCH_SOFTIRQS 5 > > #endif /* __ASM_SOFTIRQ_H__ */ > > David > > _______________________________________________ > Xen-devel mailing list > Xen-devel@lists.xensource.com > http://lists.xensource.com/xen-devel
On Tue, Jan 31, 2012 at 4:37 PM, David Vrabel <david.vrabel@citrix.com> wrote:> If a PCI System Error (SERR) is asserted it causes an NMI. If this NMI > occurs while the CPU is in printk() then Xen may deadlock as > pci_serr_error() calls console_force_unlock() which screws up the > console lock. > > I don''t think removing the console_force_unlock() is sufficient as it > looks like printk() is unsafe to call from NMI context. We would like > keep the diagnostic. Does the following (untested) patch to defer the > printk() to a softirq look like a valid approach? > > I also considered passing the NMI to dom0 (like other NMIs are) but I > couldn''t see how NMIs were handled in the current upstream pv-ops kernels.Thanks David. Unfortunately reproducing the error condition isn''t as consistent as I remember. In 6 manual invocations, I got one instance of PCI SERR, in which the patch worked correctly (i.e., the error message and did not crash the host). -George> > diff -r e2722b24dc09 xen/arch/x86/traps.c > --- a/xen/arch/x86/traps.c Thu Jan 26 17:43:31 2012 +0000 > +++ b/xen/arch/x86/traps.c Tue Jan 31 16:28:45 2012 +0000 > @@ -3173,6 +3173,11 @@ static void nmi_mce_softirq(void) > st->vcpu = NULL; > } > > +static void pci_serr_softirq(void) > +{ > + printk("\n\nNMI - PCI system error (SERR)\n"); > +} > + > void async_exception_cleanup(struct vcpu *curr) > { > int trap; > @@ -3259,10 +3264,11 @@ static void nmi_dom0_report(unsigned int > > static void pci_serr_error(struct cpu_user_regs *regs) > { > - console_force_unlock(); > - printk("\n\nNMI - PCI system error (SERR)\n"); > - > outb((inb(0x61) & 0x0f) | 0x04, 0x61); /* clear-and-disable the PCI > SERR error line. */ > + > + /* Would like to print a diagnostic here but can''t call printk() > + from NMI context -- raise a softirq instead. */ > + raise_softirq(PCI_SERR_SOFTIRQ); > } > > static void io_check_error(struct cpu_user_regs *regs) > @@ -3563,6 +3569,7 @@ void __init trap_init(void) > cpu_init(); > > open_softirq(NMI_MCE_SOFTIRQ, nmi_mce_softirq); > + open_softirq(PCI_SERR_SOFTIRQ, pci_serr_softirq); > } > > long register_guest_nmi_callback(unsigned long address) > diff -r e2722b24dc09 xen/include/asm-x86/softirq.h > --- a/xen/include/asm-x86/softirq.h Thu Jan 26 17:43:31 2012 +0000 > +++ b/xen/include/asm-x86/softirq.h Tue Jan 31 16:28:45 2012 +0000 > @@ -6,6 +6,7 @@ > #define VCPU_KICK_SOFTIRQ (NR_COMMON_SOFTIRQS + 2) > > #define MACHINE_CHECK_SOFTIRQ (NR_COMMON_SOFTIRQS + 3) > -#define NR_ARCH_SOFTIRQS 4 > +#define PCI_SERR_SOFTIRQ (NR_COMMON_SOFTIRQS + 4) > +#define NR_ARCH_SOFTIRQS 5 > > #endif /* __ASM_SOFTIRQ_H__ */ > > David > > _______________________________________________ > Xen-devel mailing list > Xen-devel@lists.xensource.com > http://lists.xensource.com/xen-devel