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SRCU uses two per-cpu counters: a nesting counter to count the number of active critical sections, and a sequence counter to ensure that the nesting counters don't change while they are being added together in srcu_readers_active_idx_check(). This patch instead uses per-cpu lock and unlock counters. Because both counters only increase and srcu_readers_active_idx_check() reads the unlock counter before the lock counter, this achieves the same end without having to increment two different counters in srcu_read_lock(). This also saves a smp_mb() in srcu_readers_active_idx_check(). Possible bug: There is no guarantee that the lock counter won't overflow during srcu_readers_active_idx_check(), as there are no memory barriers around srcu_flip() (see comment in srcu_readers_active_idx_check() for details). However, this problem was already present before this patch. Suggested-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Signed-off-by: Lance Roy <ldr709@gmail.com> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Lai Jiangshan <jiangshanlai@gmail.com> Cc: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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.