linux/kernel/rcu, branch v6.7

Merge tag 'rcu-fixes-v6.7' of git://git.kernel.org/pub/scm/linux/kernel/git/frederic/linux-dynticks

2023-11-08T17:47:52Z

Pull RCU fixes from Frederic Weisbecker: - Fix a lock inversion between scheduler and RCU introduced in v6.2-rc4. The scenario could trigger on any user of RCU_NOCB (mostly Android but also nohz_full) - Fix PF_IDLE semantic changes introduced in v6.6-rc3 breaking some RCU-Tasks and RCU-Tasks-Trace expectations as to what exactly is an idle task. This resulted in potential spurious stalls and warnings. * tag 'rcu-fixes-v6.7' of git://git.kernel.org/pub/scm/linux/kernel/git/frederic/linux-dynticks: rcu/tasks-trace: Handle new PF_IDLE semantics rcu/tasks: Handle new PF_IDLE semantics rcu: Introduce rcu_cpu_online() rcu: Break rcu_node_0 --> &rq->__lock order

Merge tag 'mm-stable-2023-11-01-14-33' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

2023-11-03T05:38:47Z

Pull MM updates from Andrew Morton: "Many singleton patches against the MM code. The patch series which are included in this merge do the following: - Kemeng Shi has contributed some compation maintenance work in the series 'Fixes and cleanups to compaction' - Joel Fernandes has a patchset ('Optimize mremap during mutual alignment within PMD') which fixes an obscure issue with mremap()'s pagetable handling during a subsequent exec(), based upon an implementation which Linus suggested - More DAMON/DAMOS maintenance and feature work from SeongJae Park i the following patch series: mm/damon: misc fixups for documents, comments and its tracepoint mm/damon: add a tracepoint for damos apply target regions mm/damon: provide pseudo-moving sum based access rate mm/damon: implement DAMOS apply intervals mm/damon/core-test: Fix memory leaks in core-test mm/damon/sysfs-schemes: Do DAMOS tried regions update for only one apply interval - In the series 'Do not try to access unaccepted memory' Adrian Hunter provides some fixups for the recently-added 'unaccepted memory' feature. To increase the feature's checking coverage. 'Plug a few gaps where RAM is exposed without checking if it is unaccepted memory' - In the series 'cleanups for lockless slab shrink' Qi Zheng has done some maintenance work which is preparation for the lockless slab shrinking code - Qi Zheng has redone the earlier (and reverted) attempt to make slab shrinking lockless in the series 'use refcount+RCU method to implement lockless slab shrink' - David Hildenbrand contributes some maintenance work for the rmap code in the series 'Anon rmap cleanups' - Kefeng Wang does more folio conversions and some maintenance work in the migration code. Series 'mm: migrate: more folio conversion and unification' - Matthew Wilcox has fixed an issue in the buffer_head code which was causing long stalls under some heavy memory/IO loads. Some cleanups were added on the way. Series 'Add and use bdev_getblk()' - In the series 'Use nth_page() in place of direct struct page manipulation' Zi Yan has fixed a potential issue with the direct manipulation of hugetlb page frames - In the series 'mm: hugetlb: Skip initialization of gigantic tail struct pages if freed by HVO' has improved our handling of gigantic pages in the hugetlb vmmemmep optimizaton code. This provides significant boot time improvements when significant amounts of gigantic pages are in use - Matthew Wilcox has sent the series 'Small hugetlb cleanups' - code rationalization and folio conversions in the hugetlb code - Yin Fengwei has improved mlock()'s handling of large folios in the series 'support large folio for mlock' - In the series 'Expose swapcache stat for memcg v1' Liu Shixin has added statistics for memcg v1 users which are available (and useful) under memcg v2 - Florent Revest has enhanced the MDWE (Memory-Deny-Write-Executable) prctl so that userspace may direct the kernel to not automatically propagate the denial to child processes. The series is named 'MDWE without inheritance' - Kefeng Wang has provided the series 'mm: convert numa balancing functions to use a folio' which does what it says - In the series 'mm/ksm: add fork-exec support for prctl' Stefan Roesch makes is possible for a process to propagate KSM treatment across exec() - Huang Ying has enhanced memory tiering's calculation of memory distances. This is used to permit the dax/kmem driver to use 'high bandwidth memory' in addition to Optane Data Center Persistent Memory Modules (DCPMM). The series is named 'memory tiering: calculate abstract distance based on ACPI HMAT' - In the series 'Smart scanning mode for KSM' Stefan Roesch has optimized KSM by teaching it to retain and use some historical information from previous scans - Yosry Ahmed has fixed some inconsistencies in memcg statistics in the series 'mm: memcg: fix tracking of pending stats updates values' - In the series 'Implement IOCTL to get and optionally clear info about PTEs' Peter Xu has added an ioctl to /proc//pagemap which permits us to atomically read-then-clear page softdirty state. This is mainly used by CRIU - Hugh Dickins contributed the series 'shmem,tmpfs: general maintenance', a bunch of relatively minor maintenance tweaks to this code - Matthew Wilcox has increased the use of the VMA lock over file-backed page faults in the series 'Handle more faults under the VMA lock'. Some rationalizations of the fault path became possible as a result - In the series 'mm/rmap: convert page_move_anon_rmap() to folio_move_anon_rmap()' David Hildenbrand has implemented some cleanups and folio conversions - In the series 'various improvements to the GUP interface' Lorenzo Stoakes has simplified and improved the GUP interface with an eye to providing groundwork for future improvements - Andrey Konovalov has sent along the series 'kasan: assorted fixes and improvements' which does those things - Some page allocator maintenance work from Kemeng Shi in the series 'Two minor cleanups to break_down_buddy_pages' - In thes series 'New selftest for mm' Breno Leitao has developed another MM self test which tickles a race we had between madvise() and page faults - In the series 'Add folio_end_read' Matthew Wilcox provides cleanups and an optimization to the core pagecache code - Nhat Pham has added memcg accounting for hugetlb memory in the series 'hugetlb memcg accounting' - Cleanups and rationalizations to the pagemap code from Lorenzo Stoakes, in the series 'Abstract vma_merge() and split_vma()' - Audra Mitchell has fixed issues in the procfs page_owner code's new timestamping feature which was causing some misbehaviours. In the series 'Fix page_owner's use of free timestamps' - Lorenzo Stoakes has fixed the handling of new mappings of sealed files in the series 'permit write-sealed memfd read-only shared mappings' - Mike Kravetz has optimized the hugetlb vmemmap optimization in the series 'Batch hugetlb vmemmap modification operations' - Some buffer_head folio conversions and cleanups from Matthew Wilcox in the series 'Finish the create_empty_buffers() transition' - As a page allocator performance optimization Huang Ying has added automatic tuning to the allocator's per-cpu-pages feature, in the series 'mm: PCP high auto-tuning' - Roman Gushchin has contributed the patchset 'mm: improve performance of accounted kernel memory allocations' which improves their performance by ~30% as measured by a micro-benchmark - folio conversions from Kefeng Wang in the series 'mm: convert page cpupid functions to folios' - Some kmemleak fixups in Liu Shixin's series 'Some bugfix about kmemleak' - Qi Zheng has improved our handling of memoryless nodes by keeping them off the allocation fallback list. This is done in the series 'handle memoryless nodes more appropriately' - khugepaged conversions from Vishal Moola in the series 'Some khugepaged folio conversions'" [ bcachefs conflicts with the dynamically allocated shrinkers have been resolved as per Stephen Rothwell in https://lore.kernel.org/all/20230913093553.4290421e@canb.auug.org.au/ with help from Qi Zheng. The clone3 test filtering conflict was half-arsed by yours truly ] * tag 'mm-stable-2023-11-01-14-33' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm: (406 commits) mm/damon/sysfs: update monitoring target regions for online input commit mm/damon/sysfs: remove requested targets when online-commit inputs selftests: add a sanity check for zswap Documentation: maple_tree: fix word spelling error mm/vmalloc: fix the unchecked dereference warning in vread_iter() zswap: export compression failure stats Documentation: ubsan: drop "the" from article title mempolicy: migration attempt to match interleave nodes mempolicy: mmap_lock is not needed while migrating folios mempolicy: alloc_pages_mpol() for NUMA policy without vma mm: add page_rmappable_folio() wrapper mempolicy: remove confusing MPOL_MF_LAZY dead code mempolicy: mpol_shared_policy_init() without pseudo-vma mempolicy trivia: use pgoff_t in shared mempolicy tree mempolicy trivia: slightly more consistent naming mempolicy trivia: delete those ancient pr_debug()s mempolicy: fix migrate_pages(2) syscall return nr_failed kernfs: drop shared NUMA mempolicy hooks hugetlbfs: drop shared NUMA mempolicy pretence mm/damon/sysfs-test: add a unit test for damon_sysfs_set_targets() ...

rcu/tasks-trace: Handle new PF_IDLE semantics

2023-11-01T21:12:03Z

The commit: cff9b2332ab7 ("kernel/sched: Modify initial boot task idle setup") has changed the semantics of what is to be considered an idle task in such a way that the idle task of an offline CPU may not carry the PF_IDLE flag anymore. However RCU-tasks-trace tests the opposite assertion, still assuming that idle tasks carry the PF_IDLE flag during their whole lifecycle. Remove this assumption to avoid spurious warnings but keep the initial test verifying that the idle task is the current task on any offline CPU. Reported-by: Naresh Kamboju Fixes: cff9b2332ab7 ("kernel/sched: Modify initial boot task idle setup") Suggested-by: Joel Fernandes Suggested-by: Paul E . McKenney" Acked-by: Peter Zijlstra (Intel) Signed-off-by: Frederic Weisbecker

rcu/tasks: Handle new PF_IDLE semantics

2023-11-01T21:03:56Z

The commit: cff9b2332ab7 ("kernel/sched: Modify initial boot task idle setup") has changed the semantics of what is to be considered an idle task in such a way that CPU boot code preceding the actual idle loop is excluded from it. This has however introduced new potential RCU-tasks stalls when either: 1) Grace period is started before init/0 had a chance to set PF_IDLE, keeping it stuck in the holdout list until idle ever schedules. 2) Grace period is started when some possible CPUs have never been online, keeping their idle tasks stuck in the holdout list until the CPU ever boots up. 3) Similar to 1) but with secondary CPUs: Grace period is started concurrently with secondary CPU booting, putting its idle task in the holdout list because PF_IDLE isn't yet observed on it. It stays then stuck in the holdout list until that CPU ever schedules. The effect is mitigated here by the hotplug AP thread that must run to bring the CPU up. Fix this with handling the new semantics of PF_IDLE, keeping in mind that it may or may not be set on an idle task. Take advantage of that to strengthen the coverage of an RCU-tasks quiescent state within an idle task, excluding the CPU boot code from it. Only the code running within the idle loop is now a quiescent state, along with offline CPUs. Fixes: cff9b2332ab7 ("kernel/sched: Modify initial boot task idle setup") Suggested-by: Joel Fernandes Suggested-by: Paul E . McKenney" Acked-by: Peter Zijlstra (Intel) Signed-off-by: Frederic Weisbecker

rcu: Introduce rcu_cpu_online()

2023-11-01T21:03:27Z

Export the RCU point of view as to when a CPU is considered offline (ie: when does RCU consider that a CPU is sufficiently down in the hotplug process to not feature any possible read side). This will be used by RCU-tasks whose vision of an offline CPU should reasonably match the one of RCU core. Fixes: cff9b2332ab7 ("kernel/sched: Modify initial boot task idle setup") Acked-by: Peter Zijlstra (Intel) Signed-off-by: Frederic Weisbecker

rcu: Break rcu_node_0 --> &rq->__lock order

2023-11-01T20:39:58Z

Commit 851a723e45d1 ("sched: Always clear user_cpus_ptr in do_set_cpus_allowed()") added a kfree() call to free any user provided affinity mask, if present. It was changed later to use kfree_rcu() in commit 9a5418bc48ba ("sched/core: Use kfree_rcu() in do_set_cpus_allowed()") to avoid a circular locking dependency problem. It turns out that even kfree_rcu() isn't safe for avoiding circular locking problem. As reported by kernel test robot, the following circular locking dependency now exists: &rdp->nocb_lock --> rcu_node_0 --> &rq->__lock Solve this by breaking the rcu_node_0 --> &rq->__lock chain by moving the resched_cpu() out from under rcu_node lock. [peterz: heavily borrowed from Waiman's Changelog] [paulmck: applied Z qiang feedback] Fixes: 851a723e45d1 ("sched: Always clear user_cpus_ptr in do_set_cpus_allowed()") Reported-by: kernel test robot Acked-by: Waiman Long Signed-off-by: Peter Zijlstra (Intel) Link: https://lore.kernel.org/oe-lkp/202310302207.a25f1a30-oliver.sang@intel.com Signed-off-by: Paul E. McKenney Signed-off-by: Frederic Weisbecker

Merge branches 'rcu/torture', 'rcu/fixes', 'rcu/docs', 'rcu/refscale', 'rcu/tasks' and 'rcu/stall' into rcu/next

2023-10-23T13:24:11Z

rcu/torture: RCU torture, locktorture and generic torture infrastructure rcu/fixes: Generic and misc fixes rcu/docs: RCU documentation updates rcu/refscale: RCU reference scalability test updates rcu/tasks: RCU tasks updates rcu/stall: Stall detection updates

srcu: Only accelerate on enqueue time

2023-10-13T12:00:54Z

Acceleration in SRCU happens on enqueue time for each new callback. This operation is expected not to fail and therefore any similar attempt from other places shouldn't find any remaining callbacks to accelerate. Moreover accelerations performed beyond enqueue time are error prone because rcu_seq_snap() then may return the snapshot for a new grace period that is not going to be started. Remove these dangerous and needless accelerations and introduce instead assertions reporting leaking unaccelerated callbacks beyond enqueue time. Co-developed-by: Yong He Signed-off-by: Yong He Co-developed-by: Joel Fernandes (Google) Signed-off-by: Joel Fernandes (Google) Co-developed-by: Neeraj upadhyay Signed-off-by: Neeraj upadhyay Reviewed-by: Like Xu Signed-off-by: Frederic Weisbecker

srcu: Fix callbacks acceleration mishandling

2023-10-10T14:32:26Z

SRCU callbacks acceleration might fail if the preceding callbacks advance also fails. This can happen when the following steps are met: 1) The RCU_WAIT_TAIL segment has callbacks (say for gp_num 8) and the RCU_NEXT_READY_TAIL also has callbacks (say for gp_num 12). 2) The grace period for RCU_WAIT_TAIL is observed as started but not yet completed so rcu_seq_current() returns 4 + SRCU_STATE_SCAN1 = 5. 3) This value is passed to rcu_segcblist_advance() which can't move any segment forward and fails. 4) srcu_gp_start_if_needed() still proceeds with callback acceleration. But then the call to rcu_seq_snap() observes the grace period for the RCU_WAIT_TAIL segment (gp_num 8) as completed and the subsequent one for the RCU_NEXT_READY_TAIL segment as started (ie: 8 + SRCU_STATE_SCAN1 = 9) so it returns a snapshot of the next grace period, which is 16. 5) The value of 16 is passed to rcu_segcblist_accelerate() but the freshly enqueued callback in RCU_NEXT_TAIL can't move to RCU_NEXT_READY_TAIL which already has callbacks for a previous grace period (gp_num = 12). So acceleration fails. 6) Note in all these steps, srcu_invoke_callbacks() hadn't had a chance to run srcu_invoke_callbacks(). Then some very bad outcome may happen if the following happens: 7) Some other CPU races and starts the grace period number 16 before the CPU handling previous steps had a chance. Therefore srcu_gp_start() isn't called on the latter sdp to fix the acceleration leak from previous steps with a new pair of call to advance/accelerate. 8) The grace period 16 completes and srcu_invoke_callbacks() is finally called. All the callbacks from previous grace periods (8 and 12) are correctly advanced and executed but callbacks in RCU_NEXT_READY_TAIL still remain. Then rcu_segcblist_accelerate() is called with a snaphot of 20. 9) Since nothing started the grace period number 20, callbacks stay unhandled. This has been reported in real load: [3144162.608392] INFO: task kworker/136:12:252684 blocked for more than 122 seconds. [3144162.615986] Tainted: G O K 5.4.203-1-tlinux4-0011.1 #1 [3144162.623053] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. [3144162.631162] kworker/136:12 D 0 252684 2 0x90004000 [3144162.631189] Workqueue: kvm-irqfd-cleanup irqfd_shutdown [kvm] [3144162.631192] Call Trace: [3144162.631202] __schedule+0x2ee/0x660 [3144162.631206] schedule+0x33/0xa0 [3144162.631209] schedule_timeout+0x1c4/0x340 [3144162.631214] ? update_load_avg+0x82/0x660 [3144162.631217] ? raw_spin_rq_lock_nested+0x1f/0x30 [3144162.631218] wait_for_completion+0x119/0x180 [3144162.631220] ? wake_up_q+0x80/0x80 [3144162.631224] __synchronize_srcu.part.19+0x81/0xb0 [3144162.631226] ? __bpf_trace_rcu_utilization+0x10/0x10 [3144162.631227] synchronize_srcu+0x5f/0xc0 [3144162.631236] irqfd_shutdown+0x3c/0xb0 [kvm] [3144162.631239] ? __schedule+0x2f6/0x660 [3144162.631243] process_one_work+0x19a/0x3a0 [3144162.631244] worker_thread+0x37/0x3a0 [3144162.631247] kthread+0x117/0x140 [3144162.631247] ? process_one_work+0x3a0/0x3a0 [3144162.631248] ? __kthread_cancel_work+0x40/0x40 [3144162.631250] ret_from_fork+0x1f/0x30 Fix this with taking the snapshot for acceleration _before_ the read of the current grace period number. The only side effect of this solution is that callbacks advancing happen then _after_ the full barrier in rcu_seq_snap(). This is not a problem because that barrier only cares about: 1) Ordering accesses of the update side before call_srcu() so they don't bleed. 2) See all the accesses prior to the grace period of the current gp_num The only things callbacks advancing need to be ordered against are carried by snp locking. Reported-by: Yong He Co-developed-by:: Yong He Signed-off-by: Yong He Co-developed-by: Joel Fernandes (Google) Signed-off-by: Joel Fernandes (Google) Co-developed-by: Neeraj upadhyay Signed-off-by: Neeraj upadhyay Link: http://lore.kernel.org/CANZk6aR+CqZaqmMWrC2eRRPY12qAZnDZLwLnHZbNi=xXMB401g@mail.gmail.com Fixes: da915ad5cf25 ("srcu: Parallelize callback handling") Signed-off-by: Frederic Weisbecker

rcu: Standardize explicit CPU-hotplug calls

2023-10-04T20:29:45Z

rcu_report_dead() and rcutree_migrate_callbacks() have their headers in rcupdate.h while those are pure rcutree calls, like the other CPU-hotplug functions. Also rcu_cpu_starting() and rcu_report_dead() have different naming conventions while they mirror each other's effects. Fix the headers and propose a naming that relates both functions and aligns with the prefix of other rcutree CPU-hotplug functions. Reviewed-by: Paul E. McKenney Signed-off-by: Frederic Weisbecker