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authorLinus Torvalds <torvalds@linux-foundation.org>2021-08-30 12:48:01 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2021-08-30 12:48:01 -0700
commit4ca4256453effb885c1688633676682529593f82 (patch)
treecff56102334a6cf04c2b97bc55a4c0ac3fd5b229 /kernel/sched/core.c
parent6f01c935d96cd4eb8bbbc5249bd9a754b6939e0a (diff)
parentb770efc4608d24fb446b94e1087d9989425dd39b (diff)
Merge branch 'core-rcu.2021.08.28a' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu
Pull RCU updates from Paul McKenney: "RCU changes for this cycle were: - Documentation updates - Miscellaneous fixes - Offloaded-callbacks updates - Updates to the nolibc library - Tasks-RCU updates - In-kernel torture-test updates - Torture-test scripting, perhaps most notably the pinning of torture-test guest OSes so as to force differences in memory latency. For example, in a two-socket system, a four-CPU guest OS will have one pair of its CPUs pinned to threads in a single core on one socket and the other pair pinned to threads in a single core on the other socket. This approach proved able to force race conditions that earlier testing missed. Some of these race conditions are still being tracked down" * 'core-rcu.2021.08.28a' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu: (61 commits) torture: Replace deprecated CPU-hotplug functions. rcu: Replace deprecated CPU-hotplug functions rcu: Print human-readable message for schedule() in RCU reader rcu: Explain why rcu_all_qs() is a stub in preemptible TREE RCU rcu: Use per_cpu_ptr to get the pointer of per_cpu variable rcu: Remove useless "ret" update in rcu_gp_fqs_loop() rcu: Mark accesses in tree_stall.h rcu: Make rcu_gp_init() and rcu_gp_fqs_loop noinline to conserve stack rcu: Mark lockless ->qsmask read in rcu_check_boost_fail() srcutiny: Mark read-side data races rcu: Start timing stall repetitions after warning complete rcu: Do not disable GP stall detection in rcu_cpu_stall_reset() rcu/tree: Handle VM stoppage in stall detection rculist: Unify documentation about missing list_empty_rcu() rcu: Mark accesses to ->rcu_read_lock_nesting rcu: Weaken ->dynticks accesses and updates rcu: Remove special bit at the bottom of the ->dynticks counter rcu: Fix stall-warning deadlock due to non-release of rcu_node ->lock rcu: Fix to include first blocked task in stall warning torture: Make kvm-test-1-run-qemu.sh check for reboot loops ...
Diffstat (limited to 'kernel/sched/core.c')
-rw-r--r--kernel/sched/core.c11
1 files changed, 11 insertions, 0 deletions
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index f3b27c6c5153..2b9ed1172533 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -7849,6 +7849,17 @@ int __sched __cond_resched(void)
preempt_schedule_common();
return 1;
}
+ /*
+ * In preemptible kernels, ->rcu_read_lock_nesting tells the tick
+ * whether the current CPU is in an RCU read-side critical section,
+ * so the tick can report quiescent states even for CPUs looping
+ * in kernel context. In contrast, in non-preemptible kernels,
+ * RCU readers leave no in-memory hints, which means that CPU-bound
+ * processes executing in kernel context might never report an
+ * RCU quiescent state. Therefore, the following code causes
+ * cond_resched() to report a quiescent state, but only when RCU
+ * is in urgent need of one.
+ */
#ifndef CONFIG_PREEMPT_RCU
rcu_all_qs();
#endif