[net-next,v5,00/18] Remove use of list iterator after loop body

Message

Jakob Koschel April 27, 2022, 4:06 p.m. UTC

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.a

v4->v5:
- fix reverse-xmas tree in efx_alloc_rss_context_entry() (Martin Habets)

v3->v4:
- fix build issue in efx_alloc_rss_context_entry() (Jakub Kicinski)

v2->v3:
- fix commit authors and signed-off order regarding Vladimir's patches
  (Sorry about that, wasn't intentional.)

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/[e-mail]/ [2]
Link: https://lore.kernel.org/all/CAHk-=wgRr_D8CB-D9Kg-c=[e-mail]/ [3]
Link: https://lore.kernel.org/linux-kernel/[e-mail]/ [4]
Link: https://lore.kernel.org/linux-kernel/[e-mail]/ [5]
Link: https://lore.kernel.org/linux-kernel/[e-mail]/ [6]