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net: core: device_rename: Use rwsem instead of a seqcount
Sequence counters write paths are critical sections that must never be preempted, and blocking, even for CONFIG_PREEMPTION=n, is not allowed. Commit5dbe7c178d
("net: fix kernel deadlock with interface rename and netdev name retrieval.") handled a deadlock, observed with CONFIG_PREEMPTION=n, where the devnet_rename seqcount read side was infinitely spinning: it got scheduled after the seqcount write side blocked inside its own critical section. To fix that deadlock, among other issues, the commit added a cond_resched() inside the read side section. While this will get the non-preemptible kernel eventually unstuck, the seqcount reader is fully exhausting its slice just spinning -- until TIF_NEED_RESCHED is set. The fix is also still broken: if the seqcount reader belongs to a real-time scheduling policy, it can spin forever and the kernel will livelock. Disabling preemption over the seqcount write side critical section will not work: inside it are a number of GFP_KERNEL allocations and mutex locking through the drivers/base/ :: device_rename() call chain. >From all the above, replace the seqcount with a rwsem. Fixes:5dbe7c178d
(net: fix kernel deadlock with interface rename and netdev name retrieval.) Fixes:30e6c9fa93
(net: devnet_rename_seq should be a seqcount) Fixes:c91f6df2db
(sockopt: Change getsockopt() of SO_BINDTODEVICE to return an interface name) Cc: <stable@vger.kernel.org> Reported-by: kbuild test robot <lkp@intel.com> [ v1 missing up_read() on error exit ] Reported-by: Dan Carpenter <dan.carpenter@oracle.com> [ v1 missing up_read() on error exit ] Signed-off-by: Ahmed S. Darwish <a.darwish@linutronix.de> Reviewed-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
parent
67122a7910
commit
11d6011c2c
1 changed files with 18 additions and 22 deletions
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@ -79,6 +79,7 @@
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#include <linux/sched.h>
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#include <linux/sched/mm.h>
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#include <linux/mutex.h>
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#include <linux/rwsem.h>
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#include <linux/string.h>
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#include <linux/mm.h>
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#include <linux/socket.h>
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@ -194,7 +195,7 @@ static DEFINE_SPINLOCK(napi_hash_lock);
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static unsigned int napi_gen_id = NR_CPUS;
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static DEFINE_READ_MOSTLY_HASHTABLE(napi_hash, 8);
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static seqcount_t devnet_rename_seq;
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static DECLARE_RWSEM(devnet_rename_sem);
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static inline void dev_base_seq_inc(struct net *net)
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{
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@ -998,33 +999,28 @@ EXPORT_SYMBOL(dev_get_by_napi_id);
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* @net: network namespace
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* @name: a pointer to the buffer where the name will be stored.
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* @ifindex: the ifindex of the interface to get the name from.
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*
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* The use of raw_seqcount_begin() and cond_resched() before
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* retrying is required as we want to give the writers a chance
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* to complete when CONFIG_PREEMPTION is not set.
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*/
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int netdev_get_name(struct net *net, char *name, int ifindex)
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{
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struct net_device *dev;
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unsigned int seq;
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int ret;
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retry:
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seq = raw_seqcount_begin(&devnet_rename_seq);
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down_read(&devnet_rename_sem);
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rcu_read_lock();
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dev = dev_get_by_index_rcu(net, ifindex);
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if (!dev) {
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rcu_read_unlock();
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return -ENODEV;
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ret = -ENODEV;
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goto out;
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}
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strcpy(name, dev->name);
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rcu_read_unlock();
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if (read_seqcount_retry(&devnet_rename_seq, seq)) {
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cond_resched();
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goto retry;
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}
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return 0;
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ret = 0;
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out:
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rcu_read_unlock();
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up_read(&devnet_rename_sem);
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return ret;
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}
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/**
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@ -1296,10 +1292,10 @@ int dev_change_name(struct net_device *dev, const char *newname)
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likely(!(dev->priv_flags & IFF_LIVE_RENAME_OK)))
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return -EBUSY;
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write_seqcount_begin(&devnet_rename_seq);
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down_write(&devnet_rename_sem);
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if (strncmp(newname, dev->name, IFNAMSIZ) == 0) {
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write_seqcount_end(&devnet_rename_seq);
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up_write(&devnet_rename_sem);
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return 0;
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}
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@ -1307,7 +1303,7 @@ int dev_change_name(struct net_device *dev, const char *newname)
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err = dev_get_valid_name(net, dev, newname);
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if (err < 0) {
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write_seqcount_end(&devnet_rename_seq);
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up_write(&devnet_rename_sem);
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return err;
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}
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@ -1322,11 +1318,11 @@ int dev_change_name(struct net_device *dev, const char *newname)
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if (ret) {
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memcpy(dev->name, oldname, IFNAMSIZ);
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dev->name_assign_type = old_assign_type;
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write_seqcount_end(&devnet_rename_seq);
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up_write(&devnet_rename_sem);
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return ret;
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}
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write_seqcount_end(&devnet_rename_seq);
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up_write(&devnet_rename_sem);
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netdev_adjacent_rename_links(dev, oldname);
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@ -1347,7 +1343,7 @@ int dev_change_name(struct net_device *dev, const char *newname)
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/* err >= 0 after dev_alloc_name() or stores the first errno */
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if (err >= 0) {
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err = ret;
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write_seqcount_begin(&devnet_rename_seq);
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down_write(&devnet_rename_sem);
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memcpy(dev->name, oldname, IFNAMSIZ);
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memcpy(oldname, newname, IFNAMSIZ);
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dev->name_assign_type = old_assign_type;
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