Re: [Qemu-devel] [PATCH] hw/intc: fix failure return for xics_alloc_block()

[Greg Kurz <gkurz@linux.vnet.ibm.com>]

On Mon, 8 Feb 2016 11:45:19 +1000
David Gibson <david@gibson.dropbear.id.au> wrote:

> On Fri, Feb 05, 2016 at 09:43:40AM +0100, Greg Kurz wrote:
> > From: Brian W. Hart <hartb@linux.vnet.ibm.com>
> > 
> > xics_alloc_block() does not return a clear error code when it
> > fails to allocate a block of interrupts. Instead it returns the
> > base interrupt number minus 1. This change updates it to return a
> > clear -1 in case of failure (following the example of xics_alloc()).
> > 
> > The two callers of xics_alloc_block() are updated to check for
> > a negative return as an error. They had previously checked for
> > a 0 return as an error, which wrongly treated most failures as
> > successes.
> > 
> > Fixes: bee763dbfb8cfceea112131970da07f215f293a6
> > Signed-off-by: Brian W. Hart <hartb@linux.vnet.ibm.com>
> > [only pass src and num to trace_xics_alloc_block_failed_no_left,
> >  added trace_xics_alloc_block_failed_no_left definition to trace-events]
> > Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com>  
> 
> Hrm, it would probably be better to give xics_alloc_block() an Error
> ** argument so it can report errors using the new API.
> 

Sure. I can rework the patch to do so.

> TBH the whole xics_alloc_block() interface is kind of dubious, or at
> least the ics_find_free_block() part of it.  Dynamically allocating
> irqs to devices is basically awful for migration, so it's better to
> have fixed allocations of all interrupts at the machine level.
> 

I agree about the extra complexity, but isn't it the purpose of
the ibm,change-msi RTAS call ? I'm not sure to understand what you
are suggesting...

> 
> > ---
> >  hw/intc/xics.c     |   10 ++++++----
> >  hw/ppc/spapr_pci.c |    9 +++++----
> >  trace-events       |    1 +
> >  3 files changed, 12 insertions(+), 8 deletions(-)
> > 
> > diff --git a/hw/intc/xics.c b/hw/intc/xics.c
> > index cd91ddc4d1d9..3bb77ff96e7b 100644
> > --- a/hw/intc/xics.c
> > +++ b/hw/intc/xics.c
> > @@ -763,11 +763,13 @@ int xics_alloc_block(XICSState *icp, int src, int num, bool lsi, bool align)
> >      } else {
> >          first = ics_find_free_block(ics, num, 1);
> >      }
> > +    if (first < 0) {
> > +        trace_xics_alloc_block_failed_no_left(src, num);
> > +        return -1;
> > +    }
> >  
> > -    if (first >= 0) {
> > -        for (i = first; i < first + num; ++i) {
> > -            ics_set_irq_type(ics, i, lsi);
> > -        }
> > +    for (i = first; i < first + num; ++i) {
> > +        ics_set_irq_type(ics, i, lsi);
> >      }
> >      first += ics->offset;
> >  
> > diff --git a/hw/ppc/spapr_pci.c b/hw/ppc/spapr_pci.c
> > index cca9257fecc5..ba33cee2a465 100644
> > --- a/hw/ppc/spapr_pci.c
> > +++ b/hw/ppc/spapr_pci.c
> > @@ -275,7 +275,8 @@ static void rtas_ibm_change_msi(PowerPCCPU *cpu, sPAPRMachineState *spapr,
> >      unsigned int req_num = rtas_ld(args, 4); /* 0 == remove all */
> >      unsigned int seq_num = rtas_ld(args, 5);
> >      unsigned int ret_intr_type;
> > -    unsigned int irq, max_irqs = 0, num = 0;
> > +    unsigned int max_irqs = 0, num = 0;
> > +    int irq;
> >      sPAPRPHBState *phb = NULL;
> >      PCIDevice *pdev = NULL;
> >      spapr_pci_msi *msi;
> > @@ -354,7 +355,7 @@ static void rtas_ibm_change_msi(PowerPCCPU *cpu, sPAPRMachineState *spapr,
> >      /* Allocate MSIs */
> >      irq = xics_alloc_block(spapr->icp, 0, req_num, false,
> >                             ret_intr_type == RTAS_TYPE_MSI);
> > -    if (!irq) {
> > +    if (irq < 0) {
> >          error_report("Cannot allocate MSIs for device %x", config_addr);
> >          rtas_st(rets, 0, RTAS_OUT_HW_ERROR);
> >          return;
> > @@ -1359,10 +1360,10 @@ static void spapr_phb_realize(DeviceState *dev, Error **errp)
> >  
> >      /* Initialize the LSI table */
> >      for (i = 0; i < PCI_NUM_PINS; i++) {
> > -        uint32_t irq;
> > +        int32_t irq;
> >  
> >          irq = xics_alloc_block(spapr->icp, 0, 1, true, false);
> > -        if (!irq) {
> > +        if (irq < 0) {
> >              error_setg(errp, "spapr_allocate_lsi failed");
> >              return;
> >          }
> > diff --git a/trace-events b/trace-events
> > index c9ac144ceee4..07b0250aaf11 100644
> > --- a/trace-events
> > +++ b/trace-events
> > @@ -1393,6 +1393,7 @@ xics_alloc(int src, int irq) "source#%d, irq %d"
> >  xics_alloc_failed_hint(int src, int irq) "source#%d, irq %d is already in use"
> >  xics_alloc_failed_no_left(int src) "source#%d, no irq left"
> >  xics_alloc_block(int src, int first, int num, bool lsi, int align) "source#%d, first irq %d, %d irqs, lsi=%d, alignnum %d"
> > +xics_alloc_block_failed_no_left(int src, int num) "source#%d, cannot find %d consecutive irqs"
> >  xics_ics_free(int src, int irq, int num) "Source#%d, first irq %d, %d irqs"
> >  xics_ics_free_warn(int src, int irq) "Source#%d, irq %d is already free"
> >  
> >   
>