diff options
| author | Tejun Heo <tj@kernel.org> | 2013-06-28 10:34:48 -0700 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2013-09-26 16:52:47 -0700 |
| commit | c97081c634fdee51845ca8a30f394cf06125a509 (patch) | |
| tree | 36510417cbcf9975e4995d15bfb9b76545b31ca2 | |
| parent | ff819a0c7f12179d197aa06841087964dd2be7d3 (diff) | |
rculist: list_first_or_null_rcu() should use list_entry_rcu()
commit c34ac00caefbe49d40058ae7200bd58725cebb45 upstream.
list_first_or_null() should test whether the list is empty and return
pointer to the first entry if not in a RCU safe manner. It's broken
in several ways.
* It compares __kernel @__ptr with __rcu @__next triggering the
following sparse warning.
net/core/dev.c:4331:17: error: incompatible types in comparison expression (different address spaces)
* It doesn't perform rcu_dereference*() and computes the entry address
using container_of() directly from the __rcu pointer which is
inconsitent with other rculist interface. As a result, all three
in-kernel users - net/core/dev.c, macvlan, cgroup - are buggy. They
dereference the pointer w/o going through read barrier.
* While ->next dereference passes through list_next_rcu(), the
compiler is still free to fetch ->next more than once and thus
nullify the "__ptr != __next" condition check.
Fix it by making list_first_or_null_rcu() dereference ->next directly
using ACCESS_ONCE() and then use list_entry_rcu() on it like other
rculist accessors.
v2: Paul pointed out that the compiler may fetch the pointer more than
once nullifying the condition check. ACCESS_ONCE() added on
->next dereference.
v3: Restored () around macro param which was accidentally removed.
Spotted by Paul.
Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: Fengguang Wu <fengguang.wu@intel.com>
Cc: Dipankar Sarma <dipankar@in.ibm.com>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Li Zefan <lizefan@huawei.com>
Cc: Patrick McHardy <kaber@trash.net>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
| -rw-r--r-- | include/linux/rculist.h | 5 |
1 files changed, 3 insertions, 2 deletions
diff --git a/include/linux/rculist.h b/include/linux/rculist.h index c30ffd87e5f..52d280bab0b 100644 --- a/include/linux/rculist.h +++ b/include/linux/rculist.h @@ -254,8 +254,9 @@ static inline void list_splice_init_rcu(struct list_head *list, */ #define list_first_or_null_rcu(ptr, type, member) \ ({struct list_head *__ptr = (ptr); \ - struct list_head __rcu *__next = list_next_rcu(__ptr); \ - likely(__ptr != __next) ? container_of(__next, type, member) : NULL; \ + struct list_head *__next = ACCESS_ONCE(__ptr->next); \ + likely(__ptr != __next) ? \ + list_entry_rcu(__next, type, member) : NULL; \ }) /** |