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   1 From: Maharaja Kennadyrajan <maharaja.kennadyrajan@oss.qualcomm.com>
   2 Date: Fri, 18 Jul 2025 11:38:35 +0530
   3 Subject: [PATCH] wifi: mac80211: Add link iteration macro for link data
   4  with rcu_dereference
   5
   6 Currently, the existing macro for_each_link_data() uses sdata_dereference()
   7 which requires the wiphy lock. This lock cannot be used in atomic or RCU
   8 read-side contexts, such as in the RX path.
   9
  10 Introduce a new macro, for_each_link_data_rcu(), that iterates over link of
  11 sdata using rcu_dereference(), making it safe to use in RCU contexts. This
  12 allows callers to access link data without requiring the wiphy lock.
  13
  14 The macro takes into account the vif.valid_links bitmap and ensures only
  15 valid links are accessed safely. Callers are responsible for ensuring that
  16 rcu_read_lock() is held when using this macro.
  17
  18 Signed-off-by: Maharaja Kennadyrajan <maharaja.kennadyrajan@oss.qualcomm.com>
  19 Link: https://patch.msgid.link/20250718060837.59371-3-maharaja.kennadyrajan@oss.qualcomm.com
  20 Signed-off-by: Johannes Berg <johannes.berg@intel.com>
  21 ---
  22
  23 --- a/net/mac80211/ieee80211_i.h
  24 +++ b/net/mac80211/ieee80211_i.h
  25 @@ -1237,6 +1237,19 @@ struct ieee80211_sub_if_data *vif_to_sda
  26                     ((__link) = sdata_dereference((__sdata)->link[__link_id],   \
  27                                                   (__sdata))))
  28
  29 +/*
  30 + * for_each_link_data_rcu should be used under RCU read lock.
  31 + */
  32 +#define for_each_link_data_rcu(sdata, __link)                                  \
  33 +       /* outer loop just to define the variable ... */                        \
  34 +       for (struct ieee80211_sub_if_data *__sdata = (sdata); __sdata;          \
  35 +               __sdata = NULL /* always stop */)                               \
  36 +       for (int __link_id = 0;                                                 \
  37 +            __link_id < ARRAY_SIZE((__sdata)->link); __link_id++)              \
  38 +               if ((!(__sdata)->vif.valid_links ||                             \
  39 +                    (__sdata)->vif.valid_links & BIT(__link_id)) &&            \
  40 +                   ((__link) = rcu_dereference((__sdata)->link[__link_id])))   \
  41 +
  42  static inline int
  43  ieee80211_get_mbssid_beacon_len(struct cfg80211_mbssid_elems *elems,
  44                                 struct cfg80211_rnr_elems *rnr_elems,