user/sven/linux.git/kernel/rcu, branch v5.17.1

rcu: Don't deboost before reporting expedited quiescent state

2022-03-28T08:03:21Z

commit 10c535787436d62ea28156a4b91365fd89b5a432 upstream. Currently rcu_preempt_deferred_qs_irqrestore() releases rnp->boost_mtx before reporting the expedited quiescent state. Under heavy real-time load, this can result in this function being preempted before the quiescent state is reported, which can in turn prevent the expedited grace period from completing. Tim Murray reports that the resulting expedited grace periods can take hundreds of milliseconds and even more than one second, when they should normally complete in less than a millisecond. This was fine given that there were no particular response-time constraints for synchronize_rcu_expedited(), as it was designed for throughput rather than latency. However, some users now need sub-100-millisecond response-time constratints. This patch therefore follows Neeraj's suggestion (seconded by Tim and by Uladzislau Rezki) of simply reversing the two operations. Reported-by: Tim Murray Reported-by: Joel Fernandes Reported-by: Neeraj Upadhyay Reviewed-by: Neeraj Upadhyay Reviewed-by: Uladzislau Rezki (Sony) Tested-by: Tim Murray Cc: Todd Kjos Cc: Sandeep Patil Cc: # 5.4.x Signed-off-by: Paul E. McKenney Signed-off-by: Greg Kroah-Hartman

rcu-tasks: Fix computation of CPU-to-list shift counts

2022-01-26T21:04:05Z

The ->percpu_enqueue_shift field is used to map from the running CPU number to the index of the corresponding callback list. This mapping can change at runtime in response to varying callback load, resulting in varying levels of contention on the callback-list locks. Unfortunately, the initial value of this field is correct only if the system happens to have a power-of-two number of CPUs, otherwise the callbacks from the high-numbered CPUs can be placed into the callback list indexed by 1 (rather than 0), and those index-1 callbacks will be ignored. This can result in soft lockups and hangs. This commit therefore corrects this mapping, adding one to this shift count as needed for systems having odd numbers of CPUs. Fixes: 7a30871b6a27 ("rcu-tasks: Introduce ->percpu_enqueue_shift for dynamic queue selection") Reported-by: Andrii Nakryiko Cc: Reported-by: Martin Lau Cc: Neeraj Upadhyay Signed-off-by: Paul E. McKenney

Merge branch 'akpm' (patches from Andrew)

2022-01-15T18:37:06Z

Merge misc updates from Andrew Morton: "146 patches. Subsystems affected by this patch series: kthread, ia64, scripts, ntfs, squashfs, ocfs2, vfs, and mm (slab-generic, slab, kmemleak, dax, kasan, debug, pagecache, gup, shmem, frontswap, memremap, memcg, selftests, pagemap, dma, vmalloc, memory-failure, hugetlb, userfaultfd, vmscan, mempolicy, oom-kill, hugetlbfs, migration, thp, ksm, page-poison, percpu, rmap, zswap, zram, cleanups, hmm, and damon)" * emailed patches from Andrew Morton : (146 commits) mm/damon: hide kernel pointer from tracepoint event mm/damon/vaddr: hide kernel pointer from damon_va_three_regions() failure log mm/damon/vaddr: use pr_debug() for damon_va_three_regions() failure logging mm/damon/dbgfs: remove an unnecessary variable mm/damon: move the implementation of damon_insert_region to damon.h mm/damon: add access checking for hugetlb pages Docs/admin-guide/mm/damon/usage: update for schemes statistics mm/damon/dbgfs: support all DAMOS stats Docs/admin-guide/mm/damon/reclaim: document statistics parameters mm/damon/reclaim: provide reclamation statistics mm/damon/schemes: account how many times quota limit has exceeded mm/damon/schemes: account scheme actions that successfully applied mm/damon: remove a mistakenly added comment for a future feature Docs/admin-guide/mm/damon/usage: update for kdamond_pid and (mk|rm)_contexts Docs/admin-guide/mm/damon/usage: mention tracepoint at the beginning Docs/admin-guide/mm/damon/usage: remove redundant information Docs/admin-guide/mm/damon/usage: update for scheme quotas and watermarks mm/damon: convert macro functions to static inline functions mm/damon: modify damon_rand() macro to static inline function mm/damon: move damon_rand() definition into damon.h ...

rcutorture: make use of the helper function kthread_run_on_cpu()

2022-01-15T14:30:24Z

Replace kthread_create_on_node/kthread_bind/wake_up_process() with kthread_run_on_cpu() to simplify the code. Link: https://lkml.kernel.org/r/20211022025711.3673-5-caihuoqing@baidu.com Signed-off-by: Cai Huoqing Cc: Bernard Metzler Cc: Daniel Bristot de Oliveira Cc: Davidlohr Bueso Cc: Doug Ledford Cc: Ingo Molnar Cc: Jason Gunthorpe Cc: Joel Fernandes (Google) Cc: Josh Triplett Cc: Lai Jiangshan Cc: Mathieu Desnoyers Cc: "Paul E . McKenney" Cc: Steven Rostedt Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

Merge branches 'doc.2021.11.30c', 'exp.2021.12.07a', 'fastnohz.2021.11.30c', 'fixes.2021.11.30c', 'nocb.2021.12.09a', 'nolibc.2021.11.30c', 'tasks.2021.12.09a', 'torture.2021.12.07a' and 'torturescript.2021.11.30c' into HEAD

2021-12-09T19:38:09Z

doc.2021.11.30c: Documentation updates. exp.2021.12.07a: Expedited-grace-period fixes. fastnohz.2021.11.30c: Remove CONFIG_RCU_FAST_NO_HZ. fixes.2021.11.30c: Miscellaneous fixes. nocb.2021.12.09a: No-CB CPU updates. nolibc.2021.11.30c: Tiny in-kernel library updates. tasks.2021.12.09a: RCU-tasks updates, including update-side scalability. torture.2021.12.07a: Torture-test in-kernel module updates. torturescript.2021.11.30c: Torture-test scripting updates.

rcu/nocb: Merge rcu_spawn_cpu_nocb_kthread() and rcu_spawn_one_nocb_kthread()

2021-12-09T19:35:16Z

The rcu_spawn_one_nocb_kthread() function is called only from rcu_spawn_cpu_nocb_kthread(). Therefore, inline the former into the latter, saving a few lines of code. Reviewed-by: Neeraj Upadhyay Signed-off-by: Frederic Weisbecker Cc: Boqun Feng Cc: Uladzislau Rezki Cc: Josh Triplett Cc: Joel Fernandes Tested-by: Juri Lelli Signed-off-by: Paul E. McKenney

rcu/nocb: Allow empty "rcu_nocbs" kernel parameter

2021-12-09T19:35:11Z

Allow the rcu_nocbs kernel parameter to be specified just by itself, without specifying any CPUs. This allows systems administrators to use "rcu_nocbs" to specify that none of the CPUs are to be offloaded at boot time, but than any of them may be offloaded at runtime via cpusets. In contrast, if the "rcu_nocbs" or "nohz_full" kernel parameters are not specified at all, then not only are none of the CPUs offloaded at boot, none of them can be offloaded at runtime, either. While in the area, modernize the description of the "rcuo" kthreads' naming scheme. Reviewed-by: Neeraj Upadhyay Signed-off-by: Frederic Weisbecker Cc: Boqun Feng Cc: Uladzislau Rezki Cc: Josh Triplett Cc: Joel Fernandes Tested-by: Juri Lelli Signed-off-by: Paul E. McKenney

rcu/nocb: Create kthreads on all CPUs if "rcu_nocbs=" or "nohz_full=" are passed

2021-12-09T19:35:06Z

In order to be able to (de-)offload any CPU using cpusets in the future, create the NOCB data structures for all possible CPUs. For now this is done only as long as the "rcu_nocbs=" or "nohz_full=" kernel parameters are passed to avoid the unnecessary overhead for most users. Note that the rcuog and rcuoc kthreads are not created until at least one of the corresponding CPUs comes online. This approach avoids the creation of excess kthreads when firmware lies about the number of CPUs present on the system. Reviewed-by: Neeraj Upadhyay Signed-off-by: Frederic Weisbecker Cc: Boqun Feng Cc: Uladzislau Rezki Cc: Josh Triplett Cc: Joel Fernandes Tested-by: Juri Lelli Signed-off-by: Paul E. McKenney

rcu/nocb: Optimize kthreads and rdp initialization

2021-12-09T19:34:37Z

Currently cpumask_available() is used to prevent from unwanted NOCB initialization. However if neither "rcu_nocbs=" nor "nohz_full=" parameters are passed to a kernel built with CONFIG_CPUMASK_OFFSTACK=n, the initialization path is still taken, running through all sorts of needless operations and iterations on an empty cpumask. Fix this by relying on a real initialization state instead. This also optimizes kthread creation, preventing needless iteration over all online CPUs when the kernel is booted without any offloaded CPUs. Reviewed-by: Neeraj Upadhyay Signed-off-by: Frederic Weisbecker Cc: Boqun Feng Cc: Uladzislau Rezki Cc: Josh Triplett Cc: Joel Fernandes Tested-by: Juri Lelli Signed-off-by: Paul E. McKenney

rcu/nocb: Prepare nocb_cb_wait() to start with a non-offloaded rdp

2021-12-09T19:34:30Z

In order to be able to toggle the offloaded state from cpusets, a nocb kthread will need to be created for all possible CPUs whenever either of the "rcu_nocbs=" or "nohz_full=" parameters are specified. Therefore, the nocb_cb_wait() kthread must be prepared to start running on a de-offloaded rdp. To accomplish this, simply move the sleeping condition to the beginning of the nocb_cb_wait() function, which prevents this kthread from attempting to invoke callbacks before the corresponding CPU is offloaded. Reviewed-by: Neeraj Upadhyay Signed-off-by: Frederic Weisbecker Cc: Boqun Feng Cc: Uladzislau Rezki Cc: Josh Triplett Cc: Joel Fernandes Tested-by: Juri Lelli Signed-off-by: Paul E. McKenney