[PATCH] module: Fix implicit type conversion

[Jiasheng Jiang]

The variable 'cpu' is defined as unsigned int.
However in the for_each_possible_cpu, its values is assigned to -1.
That doesn't make sense and in the cpumask_next() it is implicitly
type conversed to int.
It is universally accepted that the implicit type conversion is
terrible.
Also, having the good programming custom will set an example for
others.
Thus, it might be better to change the definition of 'cpu' from
unsigned int to int.

Fixes: 10fad5e ("percpu, module: implement and use is_kernel/module_percpu_address()")
Signed-off-by: Jiasheng Jiang <jias...@iscas.ac.cn>
---
kernel/module.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/module.c b/kernel/module.c
index 927d46c..f10d611 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -632,7 +632,7 @@ static void percpu_modcopy(struct module *mod,
bool __is_module_percpu_address(unsigned long addr, unsigned long *can_addr)
{
struct module *mod;
- unsigned int cpu;
+ int cpu;

preempt_disable();

--
2.7.4

[Miroslav Benes]

[CCing Luis]

Hi,

On Fri, 29 Oct 2021, Jiasheng Jiang wrote:

> The variable 'cpu' is defined as unsigned int.
> However in the for_each_possible_cpu, its values is assigned to -1.
> That doesn't make sense and in the cpumask_next() it is implicitly
> type conversed to int.
> It is universally accepted that the implicit type conversion is
> terrible.
> Also, having the good programming custom will set an example for
> others.
> Thus, it might be better to change the definition of 'cpu' from
> unsigned int to int.

Frankly, I don't see a benefit of changing this. It seems fine to me.
Moreover this is not, by far, the only place in the kernel with the same
pattern.

Miroslav

[Luis Chamberlain]

If we're going to do this we we must ask, is it really worth it and
moving forward then add a semantic patch rule which will pick up on
misuses.

@ finds_for_each_cpu_unsigned_int @
identifier x;
iterator name for_each_possible_cpu;
iterator name for_each_online_cpu;
iterator name for_each_present_cpu;
statement S;
@@

-unsigned
int x;
<+...
(
for_each_possible_cpu(x) S
|
for_each_online_cpu(x) S
|
for_each_present_cpu(x) S
)
...+>


This produces:

arch/arm/mm/cache-b15-rac.c | 2 +-
arch/arm/mm/cache-uniphier.c | 2 +-
arch/arm64/kernel/mte.c | 2 +-
arch/arm64/kernel/smp.c | 2 +-
arch/arm64/kvm/arm.c | 2 +-
arch/ia64/kernel/smp.c | 2 +-
arch/ia64/kernel/topology.c | 2 +-
arch/ia64/mm/contig.c | 4 ++--
arch/mips/kernel/mips-cm.c | 2 +-
arch/mips/kernel/mips-cpc.c | 2 +-
arch/mips/kernel/smp.c | 6 +++---
arch/mips/mm/init.c | 2 +-
arch/openrisc/kernel/smp.c | 2 +-
arch/parisc/kernel/topology.c | 2 +-
arch/powerpc/kernel/cacheinfo.c | 4 ++--
arch/powerpc/kernel/iommu.c | 2 +-
arch/powerpc/kernel/setup_32.c | 4 ++--
arch/powerpc/kernel/setup_64.c | 8 ++++----
arch/powerpc/kernel/smp.c | 2 +-
arch/powerpc/mm/numa.c | 2 +-
arch/powerpc/platforms/ps3/interrupt.c | 2 +-
arch/powerpc/platforms/pseries/hotplug-cpu.c | 6 +++---
arch/powerpc/platforms/pseries/mobility.c | 2 +-
arch/powerpc/platforms/pseries/setup.c | 2 +-
arch/s390/pci/pci_irq.c | 4 ++--
arch/sh/kernel/topology.c | 2 +-
arch/sh/mm/cache-j2.c | 6 +++---
arch/sparc/kernel/iommu-common.c | 2 +-
arch/sparc/kernel/smp_64.c | 4 ++--
arch/x86/events/amd/uncore.c | 4 ++--
arch/x86/kernel/apic/apic_numachip.c | 2 +-
arch/x86/kernel/apic/bigsmp_32.c | 2 +-
arch/x86/kernel/apic/x2apic_cluster.c | 2 +-
arch/x86/kernel/apic/x2apic_uv_x.c | 2 +-
arch/x86/kernel/cpu/mce/apei.c | 2 +-
arch/x86/kernel/cpu/microcode/core.c | 2 +-
arch/x86/kernel/setup_percpu.c | 4 ++--
arch/x86/kernel/smpboot.c | 4 ++--
arch/x86/mm/cpu_entry_area.c | 2 +-
arch/x86/mm/pti.c | 2 +-
arch/x86/xen/mmu_pv.c | 2 +-
arch/x86/xen/smp_pv.c | 4 ++--
arch/xtensa/kernel/irq.c | 2 +-
arch/xtensa/kernel/smp.c | 4 ++--
arch/xtensa/kernel/traps.c | 2 +-
drivers/base/arch_numa.c | 2 +-
drivers/base/arch_topology.c | 2 +-
drivers/block/rnbd/rnbd-clt.c | 2 +-
drivers/cpufreq/acpi-cpufreq.c | 4 ++--
drivers/cpufreq/cpufreq_ondemand.c | 2 +-
drivers/cpufreq/intel_pstate.c | 2 +-
drivers/cpufreq/qcom-cpufreq-nvmem.c | 4 ++--
drivers/cpufreq/sun50i-cpufreq-nvmem.c | 4 ++--
drivers/idle/intel_idle.c | 2 +-
drivers/iommu/iova.c | 4 ++--
drivers/irqchip/irq-bcm6345-l1.c | 2 +-
drivers/irqchip/irq-gic.c | 2 +-
drivers/irqchip/irq-jcore-aic.c | 2 +-
drivers/irqchip/irq-mips-gic.c | 2 +-
drivers/macintosh/rack-meter.c | 2 +-
drivers/net/ethernet/chelsio/libcxgb/libcxgb_ppm.c | 2 +-
drivers/net/ethernet/intel/ixgbe/ixgbe_fcoe.c | 2 +-
drivers/net/ethernet/intel/ixgbe/ixgbe_main.c | 2 +-
drivers/net/ethernet/marvell/mvneta.c | 2 +-
drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c | 4 ++--
drivers/pci/controller/pcie-iproc-msi.c | 2 +-
drivers/scsi/bnx2fc/bnx2fc_fcoe.c | 2 +-
drivers/scsi/bnx2i/bnx2i_init.c | 2 +-
drivers/scsi/bnx2i/bnx2i_iscsi.c | 2 +-
drivers/scsi/fcoe/fcoe.c | 6 +++---
drivers/scsi/fcoe/fcoe_transport.c | 2 +-
drivers/scsi/libfc/fc_exch.c | 4 ++--
drivers/scsi/libfc/fc_lport.c | 2 +-
drivers/soc/bcm/brcmstb/biuctrl.c | 2 +-
drivers/xen/events/events_base.c | 2 +-
drivers/xen/events/events_fifo.c | 2 +-
fs/fscache/main.c | 2 +-
kernel/cpu.c | 4 ++--
kernel/livepatch/transition.c | 12 ++++++------
kernel/module.c | 2 +-
kernel/relay.c | 8 ++++----
kernel/sched/deadline.c | 2 +-
kernel/sched/rt.c | 2 +-
kernel/smpboot.c | 4 ++--
kernel/stop_machine.c | 2 +-
kernel/taskstats.c | 2 +-
kernel/trace/trace_hwlat.c | 4 ++--
lib/cpu_rmap.c | 6 +++---
lib/test_lockup.c | 2 +-
mm/kmemleak.c | 4 ++--
mm/percpu-vm.c | 4 ++--
mm/percpu.c | 8 ++++----
mm/slub.c | 2 +-
mm/swap_slots.c | 2 +-
net/core/dev.c | 2 +-
net/ipv4/netfilter/arp_tables.c | 2 +-
net/ipv4/netfilter/ip_tables.c | 2 +-
net/ipv4/route.c | 2 +-
net/ipv6/netfilter/ip6_tables.c | 2 +-
net/netfilter/x_tables.c | 4 ++--
net/rds/page.c | 2 +-
net/sunrpc/svc.c | 2 +-
102 files changed, 148 insertions(+), 148 deletions(-)

[Peter Zijlstra]

On Tue, Nov 09, 2021 at 12:56:38PM -0800, Luis Chamberlain wrote:

> If we're going to do this we we must ask, is it really worth it and
> moving forward then add a semantic patch rule which will pick up on
> misuses.

Please, no!

This guy has been going around sending silly patches on his own, but the
moment you add this script all the robots will join him, adding to the
pile of useless crap we get to wade through each day.

I've yet to see one of these patches fix an actual problem.

[Luis Chamberlain]

Glad we were able to swat this fly fast.

Luis