[PATCH 0/6] Remove usage of list iterator past the loop body

Jakob Koschel
2022-02-28T11:09:54Z

This is the first patch removing several categories of use cases of
the list iterator variable past the loop.
This is follow up to the discussion in:
https://lore.kernel.org/all/20220217184829.1991035-1-jakobkoschel@gmail.com/

As concluded in:
https://lore.kernel.org/all/YhdfEIwI4EdtHdym@kroah.com/
the correct use should be using a separate variable after the loop
and using a 'tmp' variable as the list iterator.
The list iterator will not point to a valid structure after the loop
if no break/goto was hit. Invalid uses of the list iterator variable
can be avoided altogether by simply using a separate pointer to
iterate the list.

Linus and Greg agreed on the following pattern:

- struct gr_request *req;
+ struct gr_request *req = NULL;
+ struct gr_request *tmp;
struct gr_ep *ep;
int ret = 0;

- list_for_each_entry(req, &ep->queue, queue) {
- if (&req->req == _req)
+ list_for_each_entry(tmp, &ep->queue, queue) {
+ if (&tmp->req == _req) {
+ req = tmp;
break;
+ }
}
- if (&req->req != _req) {
+ if (!req) {
ret = -EINVAL;
goto out;
}

With gnu89 the list iterator variable cannot yet be declared
within the for loop of the list iterator.
Moving to a more modern version of C would allow defining
the list iterator variable within the macro, limiting
the scope to the loop.
This avoids any incorrect usage past the loop altogether.

This are around 30% of the cases where the iterator
variable is used past the loop (identified with a slightly
modified version of use_after_iter.cocci).
I've decided to split it into at a few patches separated
by similar use cases.

Because the output of get_maintainer.pl was too big,
I included all the found lists and everyone from the
previous discussion.

Jakob Koschel (6):
drivers: usb: remove usage of list iterator past the loop body
treewide: remove using list iterator after loop body as a ptr
treewide: fix incorrect use to determine if list is empty
drivers: remove unnecessary use of list iterator variable
treewide: remove dereference of list iterator after loop body
treewide: remove check of list iterator against head past the loop
body

arch/arm/mach-mmp/sram.c | 9 ++--
arch/arm/plat-pxa/ssp.c | 28 +++++-------
arch/powerpc/sysdev/fsl_gtm.c | 4 +-
arch/x86/kernel/cpu/sgx/encl.c | 6 ++-
drivers/block/drbd/drbd_req.c | 45 ++++++++++++-------
drivers/counter/counter-chrdev.c | 26 ++++++-----
drivers/crypto/cavium/nitrox/nitrox_main.c | 11 +++--
drivers/dma/dw-edma/dw-edma-core.c | 4 +-
drivers/dma/ppc4xx/adma.c | 11 +++--
drivers/firewire/core-transaction.c | 32 +++++++------
drivers/firewire/sbp2.c | 14 +++---
drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c | 19 +++++---
drivers/gpu/drm/drm_memory.c | 15 ++++---
drivers/gpu/drm/drm_mm.c | 17 ++++---
drivers/gpu/drm/drm_vm.c | 13 +++---
drivers/gpu/drm/gma500/oaktrail_lvds.c | 9 ++--
drivers/gpu/drm/i915/gem/i915_gem_context.c | 14 +++---
.../gpu/drm/i915/gem/i915_gem_execbuffer.c | 15 ++++---
drivers/gpu/drm/i915/gt/intel_ring.c | 15 ++++---
.../gpu/drm/nouveau/nvkm/subdev/clk/base.c | 11 +++--
.../gpu/drm/nouveau/nvkm/subdev/fb/ramgk104.c | 13 +++---
drivers/gpu/drm/scheduler/sched_main.c | 14 +++---
drivers/gpu/drm/ttm/ttm_bo.c | 19 ++++----
drivers/gpu/drm/vmwgfx/vmwgfx_kms.c | 22 +++++----
drivers/infiniband/hw/hfi1/tid_rdma.c | 16 ++++---
drivers/infiniband/hw/mlx4/main.c | 12 ++---
drivers/media/dvb-frontends/mxl5xx.c | 11 +++--
drivers/media/pci/saa7134/saa7134-alsa.c | 4 +-
drivers/media/v4l2-core/v4l2-ctrls-api.c | 31 +++++++------
drivers/misc/mei/interrupt.c | 12 ++---
.../net/ethernet/intel/i40e/i40e_ethtool.c | 3 +-
.../net/ethernet/qlogic/qede/qede_filter.c | 11 +++--
drivers/net/wireless/ath/ath6kl/htc_mbox.c | 2 +-
.../net/wireless/intel/ipw2x00/libipw_rx.c | 15 ++++---
drivers/perf/xgene_pmu.c | 13 +++---
drivers/power/supply/cpcap-battery.c | 11 +++--
drivers/scsi/lpfc/lpfc_bsg.c | 16 ++++---
drivers/scsi/scsi_transport_sas.c | 17 ++++---
drivers/scsi/wd719x.c | 12 +++--
drivers/staging/rtl8192e/rtl819x_TSProc.c | 17 +++----
drivers/staging/rtl8192e/rtllib_rx.c | 17 ++++---
.../staging/rtl8192u/ieee80211/ieee80211_rx.c | 15 ++++---
.../rtl8192u/ieee80211/rtl819x_TSProc.c | 19 ++++----
drivers/thermal/thermal_core.c | 38 ++++++++++------
drivers/usb/gadget/composite.c | 9 ++--
drivers/usb/gadget/configfs.c | 22 +++++----
drivers/usb/gadget/udc/aspeed-vhub/epn.c | 11 +++--
drivers/usb/gadget/udc/at91_udc.c | 26 ++++++-----
drivers/usb/gadget/udc/atmel_usba_udc.c | 11 +++--
drivers/usb/gadget/udc/bdc/bdc_ep.c | 11 +++--
drivers/usb/gadget/udc/fsl_qe_udc.c | 11 +++--
drivers/usb/gadget/udc/fsl_udc_core.c | 11 +++--
drivers/usb/gadget/udc/goku_udc.c | 11 +++--
drivers/usb/gadget/udc/gr_udc.c | 11 +++--
drivers/usb/gadget/udc/lpc32xx_udc.c | 11 +++--
drivers/usb/gadget/udc/max3420_udc.c | 11 +++--
drivers/usb/gadget/udc/mv_u3d_core.c | 11 +++--
drivers/usb/gadget/udc/mv_udc_core.c | 11 +++--
drivers/usb/gadget/udc/net2272.c | 12 ++---
drivers/usb/gadget/udc/net2280.c | 11 +++--
drivers/usb/gadget/udc/omap_udc.c | 11 +++--
drivers/usb/gadget/udc/pxa25x_udc.c | 11 +++--
drivers/usb/gadget/udc/s3c-hsudc.c | 11 +++--
drivers/usb/gadget/udc/tegra-xudc.c | 11 +++--
drivers/usb/gadget/udc/udc-xilinx.c | 11 +++--
drivers/usb/mtu3/mtu3_gadget.c | 11 +++--
drivers/usb/musb/musb_gadget.c | 11 +++--
drivers/vfio/mdev/mdev_core.c | 11 +++--
fs/cifs/smb2misc.c | 10 +++--
fs/f2fs/segment.c | 9 ++--
fs/proc/kcore.c | 13 +++---
kernel/debug/kdb/kdb_main.c | 36 +++++++++------
kernel/power/snapshot.c | 10 +++--
kernel/trace/ftrace.c | 22 +++++----
kernel/trace/trace_eprobe.c | 15 ++++---
kernel/trace/trace_events.c | 11 ++---
net/9p/trans_xen.c | 11 +++--
net/ipv4/udp_tunnel_nic.c | 10 +++--
net/tipc/name_table.c | 11 +++--
net/tipc/socket.c | 11 +++--
net/xfrm/xfrm_ipcomp.c | 11 +++--
sound/soc/intel/catpt/pcm.c | 13 +++---
sound/soc/sprd/sprd-mcdt.c | 13 +++---
83 files changed, 708 insertions(+), 465 deletions(-)

base-commit: 7ee022567bf9e2e0b3cd92461a2f4986ecc99673
--
2.25.1