rt-patches/0229-net-Add-a-mutex-around-devnet_rename_seq.patch

   1 From 13422180504cf326a959fde38db6b76b7d72ee9e Mon Sep 17 00:00:00 2001
   2 From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
   3 Date: Wed, 20 Mar 2013 18:06:20 +0100
   4 Subject: [PATCH 229/366] net: Add a mutex around devnet_rename_seq
   5
   6 On RT write_seqcount_begin() disables preemption and device_rename()
   7 allocates memory with GFP_KERNEL and grabs later the sysfs_mutex
   8 mutex. Serialize with a mutex and add use the non preemption disabling
   9 __write_seqcount_begin().
  10
  11 To avoid writer starvation, let the reader grab the mutex and release
  12 it when it detects a writer in progress. This keeps the normal case
  13 (no reader on the fly) fast.
  14
  15 [ tglx: Instead of replacing the seqcount by a mutex, add the mutex ]
  16
  17 Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
  18 Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
  19 ---
  20  net/core/dev.c | 34 ++++++++++++++++++++--------------
  21  1 file changed, 20 insertions(+), 14 deletions(-)
  22
  23 diff --git a/net/core/dev.c b/net/core/dev.c
  24 index 437e5fe..45b7dc7 100644
  25 --- a/net/core/dev.c
  26 +++ b/net/core/dev.c
  27 @@ -186,6 +186,7 @@ static unsigned int napi_gen_id;
  28  static DEFINE_HASHTABLE(napi_hash, 8);
  29
  30  static seqcount_t devnet_rename_seq;
  31 +static DEFINE_MUTEX(devnet_rename_mutex);
  32
  33  static inline void dev_base_seq_inc(struct net *net)
  34  {
  35 @@ -884,7 +885,8 @@ retry:
  36         strcpy(name, dev->name);
  37         rcu_read_unlock();
  38         if (read_seqcount_retry(&devnet_rename_seq, seq)) {
  39 -               cond_resched();
  40 +               mutex_lock(&devnet_rename_mutex);
  41 +               mutex_unlock(&devnet_rename_mutex);
  42                 goto retry;
  43         }
  44
  45 @@ -1153,20 +1155,17 @@ int dev_change_name(struct net_device *dev, const char *newname)
  46         if (dev->flags & IFF_UP)
  47                 return -EBUSY;
  48
  49 -       write_seqcount_begin(&devnet_rename_seq);
  50 +       mutex_lock(&devnet_rename_mutex);
  51 +       __raw_write_seqcount_begin(&devnet_rename_seq);
  52
  53 -       if (strncmp(newname, dev->name, IFNAMSIZ) == 0) {
  54 -               write_seqcount_end(&devnet_rename_seq);
  55 -               return 0;
  56 -       }
  57 +       if (strncmp(newname, dev->name, IFNAMSIZ) == 0)
  58 +               goto outunlock;
  59
  60         memcpy(oldname, dev->name, IFNAMSIZ);
  61
  62         err = dev_get_valid_name(net, dev, newname);
  63 -       if (err < 0) {
  64 -               write_seqcount_end(&devnet_rename_seq);
  65 -               return err;
  66 -       }
  67 +       if (err < 0)
  68 +               goto outunlock;
  69
  70         if (oldname[0] && !strchr(oldname, '%'))
  71                 netdev_info(dev, "renamed from %s\n", oldname);
  72 @@ -1179,11 +1178,12 @@ rollback:
  73         if (ret) {
  74                 memcpy(dev->name, oldname, IFNAMSIZ);
  75                 dev->name_assign_type = old_assign_type;
  76 -               write_seqcount_end(&devnet_rename_seq);
  77 -               return ret;
  78 +               err = ret;
  79 +               goto outunlock;
  80         }
  81
  82 -       write_seqcount_end(&devnet_rename_seq);
  83 +       __raw_write_seqcount_end(&devnet_rename_seq);
  84 +       mutex_unlock(&devnet_rename_mutex);
  85
  86         netdev_adjacent_rename_links(dev, oldname);
  87
  88 @@ -1204,7 +1204,8 @@ rollback:
  89                 /* err >= 0 after dev_alloc_name() or stores the first errno */
  90                 if (err >= 0) {
  91                         err = ret;
  92 -                       write_seqcount_begin(&devnet_rename_seq);
  93 +                       mutex_lock(&devnet_rename_mutex);
  94 +                       __raw_write_seqcount_begin(&devnet_rename_seq);
  95                         memcpy(dev->name, oldname, IFNAMSIZ);
  96                         memcpy(oldname, newname, IFNAMSIZ);
  97                         dev->name_assign_type = old_assign_type;
  98 @@ -1217,6 +1218,11 @@ rollback:
  99         }
 100
 101         return err;
 102 +
 103 +outunlock:
 104 +       __raw_write_seqcount_end(&devnet_rename_seq);
 105 +       mutex_unlock(&devnet_rename_mutex);
 106 +       return err;
 107  }
 108
 109  /**
 110 --
 111 1.9.1
 112