Merge tag 'rcu.2023.02.10a' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu

Pull RCU updates from Paul McKenney:

 - Documentation updates

 - Miscellaneous fixes, perhaps most notably:

      - Throttling callback invocation based on the number of callbacks
        that are now ready to invoke instead of on the total number of
        callbacks

      - Several patches that suppress false-positive boot-time
        diagnostics, for example, due to lockdep not yet being
        initialized

      - Make expedited RCU CPU stall warnings dump stacks of any tasks
        that are blocking the stalled grace period. (Normal RCU CPU
        stall warnings have done this for many years)

      - Lazy-callback fixes to avoid delays during boot, suspend, and
        resume. (Note that lazy callbacks must be explicitly enabled, so
        this should not (yet) affect production use cases)

 - Make kfree_rcu() and friends take advantage of polled grace periods,
   thus reducing memory footprint by almost two orders of magnitude,
   admittedly on a microbenchmark

   This also begins the transition from kfree_rcu(p) to
   kfree_rcu_mightsleep(p). This transition was motivated by bugs where
   kfree_rcu(p), which can block, was typed instead of the intended
   kfree_rcu(p, rh)

 - SRCU updates, perhaps most notably fixing a bug that causes SRCU to
   fail when booted on a system with a non-zero boot CPU. This
   surprising situation actually happens for kdump kernels on the
   powerpc architecture

   This also adds an srcu_down_read() and srcu_up_read(), which act like
   srcu_read_lock() and srcu_read_unlock(), but allow an SRCU read-side
   critical section to be handed off from one task to another

 - Clean up the now-useless SRCU Kconfig option

   There are a few more commits that are not yet acked or pulled into
   maintainer trees, and these will be in a pull request for a later
   merge window

 - RCU-tasks updates, perhaps most notably these fixes:

      - A strange interaction between PID-namespace unshare and the
        RCU-tasks grace period that results in a low-probability but
        very real hang

      - A race between an RCU tasks rude grace period on a single-CPU
        system and CPU-hotplug addition of the second CPU that can
        result in a too-short grace period

      - A race between shrinking RCU tasks down to a single callback
        list and queuing a new callback to some other CPU, but where
        that queuing is delayed for more than an RCU grace period. This
        can result in that callback being stranded on the non-boot CPU

 - Torture-test updates and fixes

 - Torture-test scripting updates and fixes

 - Provide additional RCU CPU stall-warning information in kernels built
   with CONFIG_RCU_CPU_STALL_CPUTIME=y, and restore the full five-minute
   timeout limit for expedited RCU CPU stall warnings

* tag 'rcu.2023.02.10a' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu: (80 commits)
  rcu/kvfree: Add kvfree_rcu_mightsleep() and kfree_rcu_mightsleep()
  kernel/notifier: Remove CONFIG_SRCU
  init: Remove "select SRCU"
  fs/quota: Remove "select SRCU"
  fs/notify: Remove "select SRCU"
  fs/btrfs: Remove "select SRCU"
  fs: Remove CONFIG_SRCU
  drivers/pci/controller: Remove "select SRCU"
  drivers/net: Remove "select SRCU"
  drivers/md: Remove "select SRCU"
  drivers/hwtracing/stm: Remove "select SRCU"
  drivers/dax: Remove "select SRCU"
  drivers/base: Remove CONFIG_SRCU
  rcu: Disable laziness if lazy-tracking says so
  rcu: Track laziness during boot and suspend
  rcu: Remove redundant call to rcu_boost_kthread_setaffinity()
  rcu: Allow up to five minutes expedited RCU CPU stall-warning timeouts
  rcu: Align the output of RCU CPU stall warning messages
  rcu: Add RCU stall diagnosis information
  sched: Add helper nr_context_switches_cpu()
  ...

4 files changed, 0 insertions, 28 deletions

diff --git a/fs/btrfs/Kconfig b/fs/btrfs/Kconfig
index 183e5c4aed34..37b6bab90c83 100644
--- a/fs/btrfs/Kconfig
+++ b/fs/btrfs/Kconfig
@@ -17,7 +17,6 @@ config BTRFS_FS
 	select FS_IOMAP
 	select RAID6_PQ
 	select XOR_BLOCKS
-	select SRCU
 	depends on PAGE_SIZE_LESS_THAN_256KB
 
 	help
diff --git a/fs/locks.c b/fs/locks.c
index 624c6ac92ede..66b4eef09db5 100644
--- a/fs/locks.c
+++ b/fs/locks.c
@@ -1890,7 +1890,6 @@ int generic_setlease(struct file *filp, long arg, struct file_lock **flp,
 }
 EXPORT_SYMBOL(generic_setlease);
 
-#if IS_ENABLED(CONFIG_SRCU)
 /*
  * Kernel subsystems can register to be notified on any attempt to set
  * a new lease with the lease_notifier_chain. This is used by (e.g.) nfsd
@@ -1924,30 +1923,6 @@ void lease_unregister_notifier(struct notifier_block *nb)
 }
 EXPORT_SYMBOL_GPL(lease_unregister_notifier);
 
-#else /* !IS_ENABLED(CONFIG_SRCU) */
-static inline void
-lease_notifier_chain_init(void)
-{
-}
-
-static inline void
-setlease_notifier(long arg, struct file_lock *lease)
-{
-}
-
-int lease_register_notifier(struct notifier_block *nb)
-{
-	return 0;
-}
-EXPORT_SYMBOL_GPL(lease_register_notifier);
-
-void lease_unregister_notifier(struct notifier_block *nb)
-{
-}
-EXPORT_SYMBOL_GPL(lease_unregister_notifier);
-
-#endif /* IS_ENABLED(CONFIG_SRCU) */
-
 /**
  * vfs_setlease        -       sets a lease on an open file
  * @filp:	file pointer
diff --git a/fs/notify/Kconfig b/fs/notify/Kconfig
index c020d26ba223..c6c72c90fd25 100644
--- a/fs/notify/Kconfig
+++ b/fs/notify/Kconfig
@@ -1,7 +1,6 @@
 # SPDX-License-Identifier: GPL-2.0-only
 config FSNOTIFY
 	def_bool n
-	select SRCU
 
 source "fs/notify/dnotify/Kconfig"
 source "fs/notify/inotify/Kconfig"
diff --git a/fs/quota/Kconfig b/fs/quota/Kconfig
index b59cd172b5f9..d5a85a8062d0 100644
--- a/fs/quota/Kconfig
+++ b/fs/quota/Kconfig
@@ -6,7 +6,6 @@
 config QUOTA
 	bool "Quota support"
 	select QUOTACTL
-	select SRCU
 	help
 	  If you say Y here, you will be able to set per user limits for disk
 	  usage (also called disk quotas). Currently, it works for the