linux/kernel/rcu/srcutree.c, branch v5.1

Merge branches 'doc.2019.01.26a', 'fixes.2019.01.26a', 'sil.2019.01.26a', 'spdx.2019.02.09a', 'srcu.2019.01.26a' and 'torture.2019.01.26a' into HEAD

2019-02-09T16:47:52Z

doc.2019.01.26a: Documentation updates. fixes.2019.01.26a: Miscellaneous fixes. sil.2019.01.26a: Removal of a few more spin_is_locked() instances. spdx.2019.02.09a: Add SPDX identifiers to RCU files srcu.2019.01.26a: SRCU updates. torture.2019.01.26a: Torture-test updates.

rcu/srcu: Convert to SPDX license identifier

2019-02-09T16:43:54Z

Replace the license boiler plate with a SPDX license identifier. While in the area, update an email address. Signed-off-by: Paul E. McKenney Reviewed-by: Thomas Gleixner

srcu: Remove srcu_queue_delayed_work_on()

2019-01-25T23:36:42Z

srcu_queue_delayed_work_on() disables preemption (and therefore CPU hotplug in RCU's case) and then checks based on its own accounting if a CPU is online. If the CPU is online it uses queue_delayed_work_on() otherwise it fallbacks to queue_delayed_work(). The problem here is that queue_work() on -RT does not work with disabled preemption. queue_work_on() works also on an offlined CPU. queue_delayed_work_on() has the problem that it is possible to program a timer on an offlined CPU. This timer will fire once the CPU is online again. But until then, the timer remains programmed and nothing will happen. Add a local timer which will fire (as requested per delay) on the local CPU and then enqueue the work on the specific CPU. RCUtorture testing with SRCU-P for 24h showed no problems. Signed-off-by: Sebastian Andrzej Siewior Signed-off-by: Paul E. McKenney

srcu: Use "ssp" instead of "sp" for srcu_struct pointer

2018-11-27T17:24:17Z

In RCU, the distinction between "rsp", "rnp", and "rdp" has served well for a great many years, but in SRCU, "sp" vs. "sdp" has proven confusing. This commit therefore renames SRCU's "sp" pointers to "ssp", so that there is "ssp" for srcu_struct pointer, "snp" for srcu_node pointer, and "sdp" for srcu_data pointer. Signed-off-by: Paul E. McKenney

srcu: Lock srcu_data structure in srcu_gp_start()

2018-11-27T17:23:57Z

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: Bart Van Assche Reported-by: Christoph Hellwig Reported-by: Sebastian Kuzminsky Signed-off-by: Dennis Krein Signed-off-by: Paul E. McKenney Tested-by: Dennis Krein Cc: # 4.16.x

srcu: Prevent __call_srcu() counter wrap with read-side critical section

2018-11-09T05:54:14Z

Ever since cdf7abc4610a ("srcu: Allow use of Tiny/Tree SRCU from both process and interrupt context"), it has been permissible to use SRCU read-side critical sections in interrupt context. This allows __call_srcu() to use SRCU read-side critical sections to prevent a new SRCU grace period from ending before the call to either srcu_funnel_gp_start() or srcu_funnel_exp_start completes, thus preventing SRCU grace-period counter overflow during that time. Note that this does not permit removal of the counter-wrap checks in srcu_gp_end(). These check are necessary to handle the case where a given CPU does not interact at all with SRCU for an extended time period. This commit therefore adds an SRCU read-side critical section to __call_srcu() in order to prevent grace period counter wrap during the funnel-locking process. Signed-off-by: Paul E. McKenney

Merge branches 'doc.2018.08.30a', 'dynticks.2018.08.30b', 'srcu.2018.08.30b' and 'torture.2018.08.29a' into HEAD

2018-08-30T23:12:53Z

doc.2018.08.30a: Documentation updates dynticks.2018.08.30b: RCU flavor consolidation updates and cleanups srcu.2018.08.30b: SRCU updates torture.2018.08.29a: Torture-test updates

srcu: Make early-boot call_srcu() reuse workqueue lists

2018-08-30T23:10:49Z

Allocating a list_head structure that is almost never used, and, when used, is used only during early boot (rcu_init() and earlier), is a bit wasteful. This commit therefore eliminates that list_head in favor of the one in the work_struct structure. This is safe because the work_struct structure cannot be used until after rcu_init() returns. Reported-by: Steven Rostedt Signed-off-by: Paul E. McKenney Cc: Tejun Heo Cc: Lai Jiangshan Tested-by: Steven Rostedt (VMware)

srcu: Make call_srcu() available during very early boot

2018-08-30T23:10:19Z

Event tracing is moving to SRCU in order to take advantage of the fact that SRCU may be safely used from idle and even offline CPUs. However, event tracing can invoke call_srcu() very early in the boot process, even before workqueue_init_early() is invoked (let alone rcu_init()). Therefore, call_srcu()'s attempts to queue work fail miserably. This commit therefore detects this situation, and refrains from attempting to queue work before rcu_init() time, but does everything else that it would have done, and in addition, adds the srcu_struct to a global list. The rcu_init() function now invokes a new srcu_init() function, which is empty if CONFIG_SRCU=n. Otherwise, srcu_init() queues work for each srcu_struct on the list. This all happens early enough in boot that there is but a single CPU with interrupts disabled, which allows synchronization to be dispensed with. Of course, the queued work won't actually be invoked until after workqueue_init() is invoked, which happens shortly after the scheduler is up and running. This means that although call_srcu() may be invoked any time after per-CPU variables have been set up, there is still a very narrow window when synchronize_srcu() won't work, and this window extends from the time that the scheduler starts until the time that workqueue_init() returns. This can be fixed in a manner similar to the fix for synchronize_rcu_expedited() and friends, but until someone actually needs to use synchronize_srcu() during this window, this fix is added churn for no benefit. Finally, note that Tree SRCU's new srcu_init() function invokes queue_work() rather than the queue_delayed_work() function that is invoked post-boot. The reason is that queue_delayed_work() will (as you would expect) post a timer, and timers have not yet been initialized. So use of queue_work() avoids the complaints about use of uninitialized spinlocks that would otherwise result. Besides, some delay is already provide by the aforementioned fact that the queued work won't actually be invoked until after the scheduler is up and running. Requested-by: Steven Rostedt Signed-off-by: Paul E. McKenney Tested-by: Steven Rostedt (VMware)

rcu: Clean up flavor-related definitions and comments in srcutree.h

2018-08-30T23:03:34Z

Signed-off-by: Paul E. McKenney