| From: Sebastian Andrzej Siewior <bigeasy@linutronix.de> |
| Date: Wed, 20 Mar 2013 18:06:20 +0100 |
| Subject: [PATCH] net: Add a mutex around devnet_rename_seq |
| |
| On RT write_seqcount_begin() disables preemption and device_rename() |
| allocates memory with GFP_KERNEL and grabs later the sysfs_mutex |
| mutex. Serialize with a mutex and add use the non preemption disabling |
| __write_seqcount_begin(). |
| |
| To avoid writer starvation, let the reader grab the mutex and release |
| it when it detects a writer in progress. This keeps the normal case |
| (no reader on the fly) fast. |
| |
| [ tglx: Instead of replacing the seqcount by a mutex, add the mutex ] |
| |
| Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> |
| Signed-off-by: Thomas Gleixner <tglx@linutronix.de> |
| --- |
| net/core/dev.c | 34 ++++++++++++++++++++-------------- |
| 1 file changed, 20 insertions(+), 14 deletions(-) |
| |
| --- a/net/core/dev.c |
| +++ b/net/core/dev.c |
| @@ -167,6 +167,7 @@ DEFINE_RWLOCK(dev_base_lock); |
| EXPORT_SYMBOL(dev_base_lock); |
| |
| static seqcount_t devnet_rename_seq; |
| +static DEFINE_MUTEX(devnet_rename_mutex); |
| |
| static inline void dev_base_seq_inc(struct net *net) |
| { |
| @@ -818,7 +819,8 @@ retry: |
| strcpy(name, dev->name); |
| rcu_read_unlock(); |
| if (read_seqcount_retry(&devnet_rename_seq, seq)) { |
| - cond_resched(); |
| + mutex_lock(&devnet_rename_mutex); |
| + mutex_unlock(&devnet_rename_mutex); |
| goto retry; |
| } |
| |
| @@ -1084,30 +1086,28 @@ int dev_change_name(struct net_device *d |
| if (dev->flags & IFF_UP) |
| return -EBUSY; |
| |
| - write_seqcount_begin(&devnet_rename_seq); |
| + mutex_lock(&devnet_rename_mutex); |
| + __write_seqcount_begin(&devnet_rename_seq); |
| |
| - if (strncmp(newname, dev->name, IFNAMSIZ) == 0) { |
| - write_seqcount_end(&devnet_rename_seq); |
| - return 0; |
| - } |
| + if (strncmp(newname, dev->name, IFNAMSIZ) == 0) |
| + goto outunlock; |
| |
| memcpy(oldname, dev->name, IFNAMSIZ); |
| |
| err = dev_get_valid_name(net, dev, newname); |
| - if (err < 0) { |
| - write_seqcount_end(&devnet_rename_seq); |
| - return err; |
| - } |
| + if (err < 0) |
| + goto outunlock; |
| |
| rollback: |
| ret = device_rename(&dev->dev, dev->name); |
| if (ret) { |
| memcpy(dev->name, oldname, IFNAMSIZ); |
| - write_seqcount_end(&devnet_rename_seq); |
| - return ret; |
| + err = ret; |
| + goto outunlock; |
| } |
| |
| - write_seqcount_end(&devnet_rename_seq); |
| + __write_seqcount_end(&devnet_rename_seq); |
| + mutex_unlock(&devnet_rename_mutex); |
| |
| write_lock_bh(&dev_base_lock); |
| hlist_del_rcu(&dev->name_hlist); |
| @@ -1126,7 +1126,8 @@ rollback: |
| /* err >= 0 after dev_alloc_name() or stores the first errno */ |
| if (err >= 0) { |
| err = ret; |
| - write_seqcount_begin(&devnet_rename_seq); |
| + mutex_lock(&devnet_rename_mutex); |
| + __write_seqcount_begin(&devnet_rename_seq); |
| memcpy(dev->name, oldname, IFNAMSIZ); |
| goto rollback; |
| } else { |
| @@ -1136,6 +1137,11 @@ rollback: |
| } |
| |
| return err; |
| + |
| +outunlock: |
| + __write_seqcount_end(&devnet_rename_seq); |
| + mutex_unlock(&devnet_rename_mutex); |
| + return err; |
| } |
| |
| /** |