srcu: Lock srcu_data structure in srcu_gp_start()
commit eb4c2382272ae7ae5d81fdfa5b7a6c86146eaaa4 upstream. The srcu_gp_start() function is called with the srcu_struct structure's ->lock held, but not with the srcu_data structure's ->lock. This is problematic because this function accesses and updates the srcu_data structure's ->srcu_cblist, which is protected by that lock. Failing to hold this lock can result in corruption of the SRCU callback lists, which in turn can result in arbitrarily bad results. This commit therefore makes srcu_gp_start() acquire the srcu_data structure's ->lock across the calls to rcu_segcblist_advance() and rcu_segcblist_accelerate(), thus preventing this corruption. Reported-by: NBart Van Assche <bvanassche@acm.org> Reported-by: NChristoph Hellwig <hch@infradead.org> Reported-by: NSebastian Kuzminsky <seb.kuzminsky@gmail.com> Signed-off-by: NDennis Krein <Dennis.Krein@netapp.com> Signed-off-by: NPaul E. McKenney <paulmck@linux.ibm.com> Tested-by: NDennis Krein <Dennis.Krein@netapp.com> Cc: <stable@vger.kernel.org> # 4.16.x Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
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