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| author | Eric Dumazet <eric.dumazet@gmail.com> | 2013-05-29 09:06:27 +0000 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2013-06-27 10:34:33 -0700 |
| commit | 64274c35beebe1be22650a9353c0c33a7b8b723c (patch) | |
| tree | c57037c60b3d0416246c9d4a31477c41b3b6a7ce | |
| parent | e1b796f9408a33d18709e9fdbf18ce91dfede962 (diff) | |
| download | kernel_samsung_aries-64274c35beebe1be22650a9353c0c33a7b8b723c.zip kernel_samsung_aries-64274c35beebe1be22650a9353c0c33a7b8b723c.tar.gz kernel_samsung_aries-64274c35beebe1be22650a9353c0c33a7b8b723c.tar.bz2 | |
net: force a reload of first item in hlist_nulls_for_each_entry_rcu
[ Upstream commit c87a124a5d5e8cf8e21c4363c3372bcaf53ea190 ]
Roman Gushchin discovered that udp4_lib_lookup2() was not reloading
first item in the rcu protected list, in case the loop was restarted.
This produced soft lockups as in https://lkml.org/lkml/2013/4/16/37
rcu_dereference(X)/ACCESS_ONCE(X) seem to not work as intended if X is
ptr->field :
In some cases, gcc caches the value or ptr->field in a register.
Use a barrier() to disallow such caching, as documented in
Documentation/atomic_ops.txt line 114
Thanks a lot to Roman for providing analysis and numerous patches.
Diagnosed-by: Roman Gushchin <klamm@yandex-team.ru>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Boris Zhmurov <zhmurov@yandex-team.ru>
Signed-off-by: Roman Gushchin <klamm@yandex-team.ru>
Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
| -rw-r--r-- | include/linux/rculist_nulls.h | 7 |
1 files changed, 6 insertions, 1 deletions
diff --git a/include/linux/rculist_nulls.h b/include/linux/rculist_nulls.h index 2ae1371..1c33dd7 100644 --- a/include/linux/rculist_nulls.h +++ b/include/linux/rculist_nulls.h @@ -105,9 +105,14 @@ static inline void hlist_nulls_add_head_rcu(struct hlist_nulls_node *n, * @head: the head for your list. * @member: the name of the hlist_nulls_node within the struct. * + * The barrier() is needed to make sure compiler doesn't cache first element [1], + * as this loop can be restarted [2] + * [1] Documentation/atomic_ops.txt around line 114 + * [2] Documentation/RCU/rculist_nulls.txt around line 146 */ #define hlist_nulls_for_each_entry_rcu(tpos, pos, head, member) \ - for (pos = rcu_dereference_raw(hlist_nulls_first_rcu(head)); \ + for (({barrier();}), \ + pos = rcu_dereference_raw(hlist_nulls_first_rcu(head)); \ (!is_a_nulls(pos)) && \ ({ tpos = hlist_nulls_entry(pos, typeof(*tpos), member); 1; }); \ pos = rcu_dereference_raw(hlist_nulls_next_rcu(pos))) |