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authorTejun Heo <tj@kernel.org>2013-06-28 10:34:48 -0700
committerPaul E. McKenney <paulmck@linux.vnet.ibm.com>2013-08-18 17:40:16 -0700
commitc34ac00caefbe49d40058ae7200bd58725cebb45 (patch)
tree5f68cd7cd4f563a4f950b1312eb0d1eca4dc92e6 /init
parent1eafd31c640d6799c63136246a59d608bed93c74 (diff)
downloadop-kernel-dev-c34ac00caefbe49d40058ae7200bd58725cebb45.zip
op-kernel-dev-c34ac00caefbe49d40058ae7200bd58725cebb45.tar.gz
rculist: list_first_or_null_rcu() should use list_entry_rcu()
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> Cc: stable@vger.kernel.org Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
Diffstat (limited to 'init')
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