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If rwlock is replaced with rcu and spinlock, it is possible that the reader thread will see fn->leaf as NULL in the following scenarios: 1. fib6_add() is in progress and we have already inserted a new node but not yet inserted the route. 2. fib6_del_route() is in progress and we have already set fn->leaf to NULL but not yet freed the node because of rcu grace period. This patch makes sure all the reader threads check fn->leaf first before using it. And together with later patch to grab rcu_read_lock() and rcu_dereference() fn->leaf, it makes sure reader threads are safe when accessing fn->leaf. Signed-off-by: Wei Wang <weiwan@google.com> Signed-off-by: Martin KaFai Lau <kafai@fb.com> Signed-off-by: Eric Dumazet <edumazet@google.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.