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

[Greg Kurz]

Just pinging Alexey as well. :)

On Tue, 23 Feb 2016 18:46:44 +0100
Greg Kurz <address@hidden> wrote:

> On Wed, 10 Feb 2016 10:41:16 +0100
> Greg Kurz <address@hidden> wrote:
> 
> > On Mon, 8 Feb 2016 09:31:49 +0100
> > Greg Kurz <address@hidden> wrote:
> >   
> > > On Mon, 8 Feb 2016 11:45:19 +1000
> > > David Gibson <address@hidden> wrote:
> > >     
> > > > On Fri, Feb 05, 2016 at 09:43:40AM +0100, Greg Kurz wrote:      
> > > > > From: Brian W. Hart <address@hidden>
> > > > > 
> > > > > 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 <address@hidden>
> > > > > [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 <address@hidden>        
> > > > 
> > > > 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.
> > >     
> > 
> > The trace_xics_alloc_block_failed_no_left trace is more a debugging thing
> > than an error to be reported to the user. Also, rtas_ibm_change_msi()
> > already has a meaningful error message:
> > 
> >         error_report("Cannot allocate MSIs for device %x", config_addr);
> > 
> > So in the end, I'm not sure about the benefit of passing an Error **
> > down to xics_alloc_block().
> >   
> 
> Hi David !
> 
> Given the remarks above, do you still think we should pass Error ** ?
> 
> > > > 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...
> > >     
> > 
> > And anyway, even if the decision is made one day to have fixed
> > allocations, shouldn't we consider fixing this bug first ?
> >   
> 
> According to the following commit changelog, the dynamic allocation was
> introduced to support PCI hot(un)plug. Maybe Alexey may explain why it
> got coded this way.
> 
> commit bee763dbfb8cfceea112131970da07f215f293a6
> Author: Alexey Kardashevskiy <address@hidden>
> Date:   Fri May 30 19:34:15 2014 +1000
> 
>     spapr: Move interrupt allocator to xics
> 
> I'm not sure of the amount of reflexion and work needed to address your
> concern... Given the time frame, what about deferring xics rework to 2.7
> and fix the bug we currently have in 2.6 ?
> 
> Thanks !
> 
> --
> Greg
> 
> > Cheers.
> > 
> > --
> > Greg
> >   
> > > >       
> > > > > ---
> > > > >  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"
> > > > >  
> > > > >         
> > > >       
> > >     
> > 
> >   
> 
>