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As pointed out by Jiri, there is still a race condition between tcf_block_put() and tcf_chain_destroy() in a RCU callback. There is no way to make it correct without proper locking or synchronization, because both operate on a shared list. Locking is hard, because the only lock we can pick here is a spinlock, however, in tc_dump_tfilter() we iterate this list with a sleeping function called (tcf_chain_dump()), which makes using a lock to protect chain_list almost impossible. Jiri suggested the idea of holding a refcnt before flushing, this works because it guarantees us there would be no parallel tcf_chain_destroy() during the loop, therefore the race condition is gone. But we have to be very careful with proper synchronization with RCU callbacks. Suggested-by: Jiri Pirko <jiri@mellanox.com> Cc: Jamal Hadi Salim <jhs@mojatatu.com> Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com> Acked-by: Jiri Pirko <jiri@mellanox.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.