[PATCH net-next v2 00/18] Remove use of list iterator after loop body

Jakob Koschel
2022-04-12T11:01:09Z

When the list iterator loop does not exit early the list iterator variable
contains a type-confused pointer to a 'bogus' list element computed based
on the head [1].

Often a 'found' variable is used to ensure the list iterator
variable is only accessed after the loop body if the loop did exit early
(using a break or goto).

In other cases that list iterator variable is used in
combination to access the list member which reverses the invocation of
container_of() and brings back a "safe" pointer to the head of the list.

Since, due to this code patten, there were quite a few bugs discovered [2],
Linus concluded that the rule should be to never use the list iterator
after the loop and introduce a dedicated pointer for that [3].

With the new gnu11 standard, it will now be possible to limit the scope
of the list iterator variable to the traversal loop itself by defining
the variable within the for loop.
This, however, requires to remove all uses of the list iterator after
the loop.

Based on input from Paolo Abeni [4], Vinicius Costa Gomes [5], and
Jakub Kicinski [6], I've splitted all the net-next related changes into
two patch sets, where this is part 1.

v1->v2:
- Fixed commit message for PATCH 14/18 and used dedicated variable
pointing to the position (Edward Cree)
- Removed redundant check in mv88e6xxx_port_vlan() (Vladimir Oltean)
- Refactor mv88e6xxx_port_vlan() using separate list iterator functions
(Vladimir Oltean)
- Refactor sja1105_insert_gate_entry() to use separate list iterator
functions (Vladimir Oltean)
- Allow early return in sja1105_insert_gate_entry() if
sja1105_first_entry_longer_than() didn't find any element
(Vladimir Oltean)
- Use list_add_tail() instead of list_add() in sja1105_insert_gate_entry()
(Jakub Kicinski)
- net: netcp: also use separate 'pos' variable instead of duplicating list_add()

Link: https://lwn.net/Articles/887097/ [1]
Link: https://lore.kernel.org/linux-kernel/20220217184829.1991035-4-jakobkoschel@gmail.com/ [2]
Link: https://lore.kernel.org/all/CAHk-=wgRr_D8CB-D9Kg-c=EHreAsk5SqXPwr9Y7k9sA6cWXJ6w@mail.gmail.com/ [3]
Link: https://lore.kernel.org/linux-kernel/7393b673c626fd75f2b4f8509faa5459254fb87c.camel@redhat.com/ [4]
Link: https://lore.kernel.org/linux-kernel/877d8a3sww.fsf@intel.com/ [5]
Link: https://lore.kernel.org/linux-kernel/20220403205502.1b34415d@kernel.org/ [6]

Jakob Koschel (18):
connector: Replace usage of found with dedicated list iterator
variable
net: dsa: sja1105: remove use of iterator after list_for_each_entry()
loop
net: dsa: sja1105: reorder sja1105_first_entry_longer_than with memory
allocation
net: dsa: sja1105: use list_add_tail(pos) instead of
list_add(pos->prev)
net: dsa: mv88e6xxx: remove redundant check in mv88e6xxx_port_vlan()
net: dsa: mv88e6xxx: refactor mv88e6xxx_port_vlan()
net: dsa: Replace usage of found with dedicated list iterator variable
net: sparx5: Replace usage of found with dedicated list iterator
variable
qed: Use dedicated list iterator variable
qed: Replace usage of found with dedicated list iterator variable
qed: Remove usage of list iterator variable after the loop
net: qede: Replace usage of found with dedicated list iterator
variable
net: qede: Remove check of list iterator against head past the loop
body
sfc: Remove usage of list iterator for list_add() after the loop body
net: netcp: Remove usage of list iterator for list_add() after loop
body
ps3_gelic: Replace usage of found with dedicated list iterator
variable
ipvlan: Remove usage of list iterator variable for the loop body
team: Remove use of list iterator variable for
list_for_each_entry_from()

drivers/connector/cn_queue.c | 13 ++---
drivers/net/dsa/mv88e6xxx/chip.c | 57 ++++++++++---------
drivers/net/dsa/sja1105/sja1105_vl.c | 51 +++++++++--------
.../microchip/sparx5/sparx5_mactable.c | 25 ++++----
drivers/net/ethernet/qlogic/qed/qed_dev.c | 11 ++--
drivers/net/ethernet/qlogic/qed/qed_iwarp.c | 26 ++++-----
drivers/net/ethernet/qlogic/qed/qed_spq.c | 6 +-
.../net/ethernet/qlogic/qede/qede_filter.c | 11 ++--
drivers/net/ethernet/qlogic/qede/qede_rdma.c | 11 ++--
drivers/net/ethernet/sfc/rx_common.c | 8 ++-
drivers/net/ethernet/ti/netcp_core.c | 14 +++--
.../net/ethernet/toshiba/ps3_gelic_wireless.c | 30 +++++-----
drivers/net/ipvlan/ipvlan_main.c | 7 ++-
drivers/net/team/team.c | 20 ++++---
net/dsa/dsa.c | 11 ++--
15 files changed, 163 insertions(+), 138 deletions(-)

base-commit: 3e732ebf7316ac83e8562db7e64cc68aec390a18