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

[David Gibson]

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.

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.


> ---
>  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"
>  
> 

-- 
David Gibson                    | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
                                | _way_ _around_!
http://www.ozlabs.org/~dgibson

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