From: Sebastian Andrzej Siewior Date: Wed, 20 Mar 2013 18:06:20 +0100 Subject: net: Add a mutex around devnet_rename_seq Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/4.19/older/patches-4.19.1-rt3.tar.xz 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 Signed-off-by: Thomas Gleixner --- net/core/dev.c | 34 ++++++++++++++++++++-------------- 1 file changed, 20 insertions(+), 14 deletions(-) --- a/net/core/dev.c +++ b/net/core/dev.c @@ -195,6 +195,7 @@ static unsigned int napi_gen_id = NR_CPU static DEFINE_READ_MOSTLY_HASHTABLE(napi_hash, 8); static seqcount_t devnet_rename_seq; +static DEFINE_MUTEX(devnet_rename_mutex); static inline void dev_base_seq_inc(struct net *net) { @@ -920,7 +921,8 @@ int netdev_get_name(struct net *net, cha 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; } @@ -1183,20 +1185,17 @@ 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); + __raw_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; if (oldname[0] && !strchr(oldname, '%')) netdev_info(dev, "renamed from %s\n", oldname); @@ -1209,11 +1208,12 @@ int dev_change_name(struct net_device *d if (ret) { memcpy(dev->name, oldname, IFNAMSIZ); dev->name_assign_type = old_assign_type; - write_seqcount_end(&devnet_rename_seq); - return ret; + err = ret; + goto outunlock; } - write_seqcount_end(&devnet_rename_seq); + __raw_write_seqcount_end(&devnet_rename_seq); + mutex_unlock(&devnet_rename_mutex); netdev_adjacent_rename_links(dev, oldname); @@ -1234,7 +1234,8 @@ int dev_change_name(struct net_device *d /* 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); + __raw_write_seqcount_begin(&devnet_rename_seq); memcpy(dev->name, oldname, IFNAMSIZ); memcpy(oldname, newname, IFNAMSIZ); dev->name_assign_type = old_assign_type; @@ -1247,6 +1248,11 @@ int dev_change_name(struct net_device *d } return err; + +outunlock: + __raw_write_seqcount_end(&devnet_rename_seq); + mutex_unlock(&devnet_rename_mutex); + return err; } /**