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

* [PATCH 0/6] Remove usage of list iterator past the loop body
@ 2022-02-28 11:08 ` Jakob Koschel
  0 siblings, 0 replies; 596+ messages in thread
From: Jakob Koschel @ 2022-02-28 11:08 UTC (permalink / raw)
  To: Linus Torvalds
  Cc: Jakob Koschel, linux-arch, Thomas Gleixner, Arnd Bergman,
	Andy Shevchenko, Andrew Morton, Kees Cook, Mike Rapoport,
	Gustavo A. R. Silva, Brian Johannesmeyer, Cristiano Giuffrida,
	Bos, H.J.,
	Christophe JAILLET, Dan Carpenter, Jason Gunthorpe,
	Rasmus Villemoes, Nathan Chancellor, linux-arm-kernel,
	linux-kernel, linuxppc-dev, linux-sgx, drbd-dev, linux-block,
	linux-iio, linux-crypto, dmaengine, linux1394-devel, amd-gfx,
	dri-devel, intel-gfx, nouveau, linux-rdma, linux-media,
	intel-wired-lan, netdev, linux-wireless, linux-pm, linux-scsi,
	linux-staging, linux-usb, linux-aspeed, bcm-kernel-feedback-list,
	linux-tegra, linux-mediatek, kvm, linux-cifs, samba-technical,
	linux-f2fs-devel, linux-fsdevel, kgdb-bugreport, v9fs-developer,
	tipc-discussion, alsa-devel

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

^ permalink raw reply	[flat|nested] 596+ messages in thread