1. 06 Apr, 2022 39 commits
  2. 05 Apr, 2022 1 commit
    • Johannes Berg's avatar
      net: ensure net_todo_list is processed quickly · 0b5c21bb
      Johannes Berg authored
      In [1], Will raised a potential issue that the cfg80211 code,
      which does (from a locking perspective)
      
        rtnl_lock()
        wiphy_lock()
        rtnl_unlock()
      
      might be suspectible to ABBA deadlocks, because rtnl_unlock()
      calls netdev_run_todo(), which might end up calling rtnl_lock()
      again, which could then deadlock (see the comment in the code
      added here for the scenario).
      
      Some back and forth and thinking ensued, but clearly this can't
      happen if the net_todo_list is empty at the rtnl_unlock() here.
      Clearly, the code here cannot actually put an entry on it, and
      all other users of rtnl_unlock() will empty it since that will
      always go through netdev_run_todo(), emptying the list.
      
      So the only other way to get there would be to add to the list
      and then unlock the RTNL without going through rtnl_unlock(),
      which is only possible through __rtnl_unlock(). However, this
      isn't exported and not used in many places, and none of them
      seem to be able to unregister before using it.
      
      Therefore, add a WARN_ON() in the code to ensure this invariant
      won't be broken, so that the cfg80211 (or any similar) code
      stays safe.
      
      [1] https://lore.kernel.org/r/Yjzpo3TfZxtKPMAG@google.comSigned-off-by: default avatarJohannes Berg <johannes.berg@intel.com>
      Link: https://lore.kernel.org/r/20220404113847.0ee02e4a70da.Ic73d206e217db20fd22dcec14fe5442ca732804b@changeidSigned-off-by: default avatarJakub Kicinski <kuba@kernel.org>
      0b5c21bb