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

__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.

No functional change when allocation succeeds.

Link: https://lore.kernel.org/all/[email protected]/ [1]
Fixes: 7dcc37b3eff9 ("powerpc/xive: Map one IPI interrupt per node")
Signed-off-by: Gou Hao <[email protected]>
Reviewed-by: Wentao Guan <[email protected]>
Reviewed-by: jiazhenyuan <[email protected]>
Suggested-by: Andrew Morton <[email protected]>
Suggested-by: Cédric Le Goater <[email protected]>
Suggested-by: Mukesh Kumar Chaurasiya (IBM) <[email protected]>
Reviewed-by: Mukesh Kumar Chaurasiya (IBM) <[email protected]>
Reviewed-by: Cédric Le Goater <[email protected]>
Reviewed-by: Andrew Morton <[email protected]>
---
 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;
-- 
2.20.1