Re: [PATCH v3 1/5] powerpc/xive: make xive IPI allocation NULL-safe

[Cédric Le Goater]

On 7/30/26 15:53, Shrikanth Hegde wrote:
> On 7/27/26 4:12 PM, Gou Hao wrote:
> > __GFP_NOFAIL should not be used in new code [1].  xive_init_ipis()
> > allocates the xive_ipis array with __GFP_NOFAIL, which makes the
> > subsequent NULL check unreachable dead code.
> >
> > Remove __GFP_NOFAIL so the allocation can fail, and make all xive_ipis
> > access paths NULL-safe:
> >
> > - Return XIVE_BAD_IRQ from xive_ipi_cpu_to_irq() when xive_ipis is NULL.
> > - Set xive_ipis to NULL after kfree() in the error path to prevent
> >    use-after-free.
> > - Guard xive_setup_cpu_ipi() and xive_cleanup_cpu_ipi() against
> >    xive_ipi_irq == XIVE_BAD_IRQ to avoid dereferencing an uninitialized
> >    or already-freed xive_ipis array.
>
> I would rather prefer a BUG_ON if the allocation fails. That keeps the earlier
> semantic.
>
> - If xive fails, then who will send the interrupts?. It is better to crash instead
> of leaving the system in weird state.

Then do like XICS, which has BUG_ON(). I don't know why we took this
direction when XIVE was first introduced.

C. 
> > No functional change when allocation succeeds.
>
> Please don't put a statement like this.
> It should be either no functional changes or function changes.
>
> > Link: https://lore.kernel.org/all/20260725202632.dcb325658896a470df91cf57@xxxxxxxxxxxxxxxxxxxx/ [1]
> > Fixes: 7dcc37b3eff9 ("powerpc/xive: Map one IPI interrupt per node")
> > Signed-off-by: Gou Hao <gouhao@xxxxxxxxxxxxx>
> > Reviewed-by: Wentao Guan <guanwentao@xxxxxxxxxxxxx>
> > Reviewed-by: jiazhenyuan <jiazhenyuan@xxxxxxxxxxxxx>
> > Suggested-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> > Suggested-by: Cédric Le Goater <clg@xxxxxxxx>
> > Suggested-by: Mukesh Kumar Chaurasiya (IBM) <mkchauras@xxxxxxxxx>
> > Reviewed-by: Mukesh Kumar Chaurasiya (IBM) <mkchauras@xxxxxxxxx>
> > Reviewed-by: Cédric Le Goater <clg@xxxxxxxx>
> > Reviewed-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> > ---
> >   arch/powerpc/sysdev/xive/common.c | 12 ++++++++++--
> >   1 file changed, 10 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/powerpc/sysdev/xive/common.c b/arch/powerpc/sysdev/xive/common.c
> > index dadd1f46ec93..86c78af1f68e 100644
> > --- a/arch/powerpc/sysdev/xive/common.c
> > +++ b/arch/powerpc/sysdev/xive/common.c
> > @@ -74,6 +74,8 @@ static struct xive_ipi_desc {
> >    */
> >   static unsigned int xive_ipi_cpu_to_irq(unsigned int cpu)
> >   {
> > +    if (!xive_ipis)
> > +        return XIVE_BAD_IRQ;
> >       return xive_ipis[early_cpu_to_node(cpu)].irq;
> >   }
> >   #endif
> > @@ -1132,8 +1134,7 @@ static int __init xive_init_ipis(void)
> >       if (!ipi_domain)
> >           goto out_free_fwnode;
> > -    xive_ipis = kzalloc_objs(*xive_ipis, nr_node_ids,
> > -                 GFP_KERNEL | __GFP_NOFAIL);
> > +    xive_ipis = kzalloc_objs(*xive_ipis, nr_node_ids, GFP_KERNEL);
> >       if (!xive_ipis)
> >           goto out_free_domain;
> > @@ -1158,6 +1159,7 @@ static int __init xive_init_ipis(void)
> >   out_free_xive_ipis:
> >       kfree(xive_ipis);
> > +    xive_ipis = NULL;
> >   out_free_domain:
> >       irq_domain_remove(ipi_domain);
> >   out_free_fwnode:
> > @@ -1190,6 +1192,9 @@ static int xive_setup_cpu_ipi(unsigned int cpu)
> >       pr_debug("Setting up IPI for CPU %d\n", cpu);
> > +    if (xive_ipi_irq == XIVE_BAD_IRQ)
> > +        return -EIO;
> > +
> >       xc = per_cpu(xive_cpu, cpu);
> >       /* Check if we are already setup */
> > @@ -1234,6 +1239,9 @@ noinstr static void xive_cleanup_cpu_ipi(unsigned int cpu, struct xive_cpu *xc)
> >       /* Disable the IPI and free the IRQ data */
> > +    if (xive_ipi_irq == XIVE_BAD_IRQ)
> > +        return;
> > +
> >       /* Already cleaned up ? */
> >       if (xc->hw_ipi == XIVE_BAD_IRQ)
> >           return;