| Message ID | 20220228110822.491923-1-jakobkoschel@gmail.com (mailing list archive) |
|---|---|
| Headers | show |
| Series | Remove usage of list iterator past the loop body | expand |
Updating this API is risky because some places rely on the old behavior and not all of them have been updated. Here are some additional places you might want to change. drivers/usb/host/uhci-q.c:466 link_async() warn: iterator used outside loop: 'pqh' drivers/infiniband/core/mad.c:968 ib_get_rmpp_segment() warn: iterator used outside loop: 'mad_send_wr->cur_seg' drivers/opp/debugfs.c:208 opp_migrate_dentry() warn: iterator used outside loop: 'new_dev' drivers/staging/greybus/audio_codec.c:602 gbcodec_mute_stream() warn: iterator used outside loop: 'module' drivers/staging/media/atomisp/pci/atomisp_acc.c:508 atomisp_acc_load_extensions() warn: iterator used outside loop: 'acc_fw' drivers/perf/thunderx2_pmu.c:814 tx2_uncore_pmu_init_dev() warn: iterator used outside loop: 'rentry' drivers/gpu/drm/nouveau/nvkm/engine/device/ctrl.c:111 nvkm_control_mthd_pstate_attr() warn: iterator used outside loop: 'pstate' drivers/gpu/drm/panfrost/panfrost_mmu.c:203 panfrost_mmu_as_get() warn: iterator used outside loop: 'lru_mmu' drivers/media/usb/uvc/uvc_v4l2.c:885 uvc_ioctl_enum_input() warn: iterator used outside loop: 'iterm' drivers/media/usb/uvc/uvc_v4l2.c:896 uvc_ioctl_enum_input() warn: iterator used outside loop: 'iterm' drivers/scsi/dc395x.c:3596 device_alloc() warn: iterator used outside loop: 'p' drivers/net/ethernet/mellanox/mlx4/alloc.c:379 __mlx4_alloc_from_zone() warn: iterator used outside loop: 'curr_node' fs/ocfs2/dlm/dlmdebug.c:573 lockres_seq_start() warn: iterator used outside loop: 'res' This patchset fixes 3 bugs. Initially when it's merged it's probably going to introduce some bugs because there are likely other places which rely on the old behavior. In an ideal world, with the new API the compiler would warn about uninitialized variables, but unfortunately that warning is disabled by default so we still have to rely on kbuild/Clang/Smatch to find the bugs. But hopefully the new API encourages people to write clearer code so it prevents bugs in the long run. regards, dan carpenter
From: Dan Carpenter > Sent: 07 March 2022 15:01 > > Updating this API is risky because some places rely on the old behavior > and not all of them have been updated. Here are some additional places > you might want to change. I really can't help thinking that trying to merge this patch is actually impossible. It affects far too many different parts of the tree. Since (I believe) this is a doubly linked list with forwards and backwards pointers that point to a 'node' (not that there is a nice comment to that effect in the header - and there are lots of ways to do linked lists) the 'head' pretty much has to be a 'node'. I'd write the following new defines (but I might be using the old names here): list_first(head, field) First item, NULL if empty. list_last(head, field) Last item NULL if empty. list_next(head, item, field) Item after 'item', NULL if last. list_prev(head, item. field) Item before 'item', NULL if first. You get (something like): #define list_first(head, field) \ head->next == &head ? NULL : list_item(head->next, field) (probably needs typeof(item) from somewhere). The iterator loop is then just: #define loop_iterate(item, head, field) \ for (item = list_first(head, field); item; \ item = list_next(head, item, field) I'm not sure, but making the 'head' be a structure that contains a single member that is a 'node' might help type checking. Then all the code that uses the current defines can slowly be moved over (probably a couple of releases) before the existing defines are deleted. That should simplify all the open-coded search loops that are just as likely to be buggy (possibly more so). David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
On Mon, Mar 7, 2022 at 7:26 AM David Laight <David.Laight@aculab.com> wrote: > > I'd write the following new defines (but I might be using > the old names here): See my email at https://lore.kernel.org/all/CAHk-=wiacQM76xec=Hr7cLchVZ8Mo9VDHmXRJzJ_EX4sOsApEA@mail.gmail.com/ for what I think is the way forward if we want to do new defines and clean up the situation. It's really just an example (and converts two list cases and one single file that uses them), so it's not in any way complete. I also has that "-std=gnu11" in the patch so that you can use the loop-declared variables - but without the other small fixups for some of the things that exposed. I'll merge the proper version of the "update C standard version" from Arnd early in the 5.18 merge window, but for testing that one file example change I sent out the patch like that. Linus
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