Commit 3ba7dfb8 authored by Linus Torvalds's avatar Linus Torvalds
Browse files

Merge tag 'rcu-next-v6.15' of git://git.kernel.org/pub/scm/linux/kernel/git/rcu/linux 

Pull RCU updates from Boqun Feng:
 "Documentation:
   - Add broken-timing possibility to stallwarn.rst
   - Improve discussion of this_cpu_ptr(), add raw_cpu_ptr()
   - Document self-propagating callbacks
   - Point call_srcu() to call_rcu() for detailed memory ordering
   - Add CONFIG_RCU_LAZY delays to call_rcu() kernel-doc header
   - Clarify RCU_LAZY and RCU_LAZY_DEFAULT_OFF help text
   - Remove references to old grace-period-wait primitives

  srcu:
   - Introduce srcu_read_{un,}lock_fast(), which is similar to
     srcu_read_{un,}lock_lite(): avoid smp_mb()s in lock and unlock
     at the cost of calling synchronize_rcu() in synchronize_srcu()

     Moreover, by returning the percpu offset of the counter at
     srcu_read_lock_fast() time, srcu_read_unlock_fast() can avoid
     extra pointer dereferencing, which makes it faster than
     srcu_read_{un,}lock_lite()

     srcu_read_{un,}lock_fast() are intended to replace
     rcu_read_{un,}lock_trace() if possible

  RCU torture:
   - Add get_torture_init_jiffies() to return the start time of the test
   - Add a test_boost_holdoff module parameter to allow delaying
     boosting tests when building rcutorture as built-in
   - Add grace period sequence number logging at the beginning and end
     of failure/close-call results
   - Switch to hexadecimal for the expedited grace period sequence
     number in the rcu_exp_grace_period trace point
   - Make cur_ops->format_gp_seqs take buffer length
   - Move RCU_TORTURE_TEST_{CHK_RDR_STATE,LOG_CPU} to bool
   - Complain when invalid SRCU reader_flavor is specified
   - Add FORCE_NEED_SRCU_NMI_SAFE Kconfig for testing, which forces SRCU
     uses atomics even when percpu ops are NMI safe, and use the Kconfig
     for SRCU lockdep testing

  Misc:
   - Split rcu_report_exp_cpu_mult() mask parameter and use for tracing
   - Remove READ_ONCE() for rdp->gpwrap access in __note_gp_changes()
   - Fix get_state_synchronize_rcu_full() GP-start detection
   - Move RCU Tasks self-tests to core_initcall()
   - Print segment lengths in show_rcu_nocb_gp_state()
   - Make RCU watch ct_kernel_exit_state() warning
   - Flush console log from kernel_power_off()
   - rcutorture: Allow a negative value for nfakewriters
   - rcu: Update TREE05.boot to test normal synchronize_rcu()
   - rcu: Use _full() API to debug synchronize_rcu()

  Make RCU handle PREEMPT_LAZY better:
   - Fix header guard for rcu_all_qs()
   - rcu: Rename PREEMPT_AUTO to PREEMPT_LAZY
   - Update __cond_resched comment about RCU quiescent states
   - Handle unstable rdp in rcu_read_unlock_strict()
   - Handle quiescent states for PREEMPT_RCU=n, PREEMPT_COUNT=y
   - osnoise: Provide quiescent states
   - Adjust rcutorture with possible PREEMPT_RCU=n && PREEMPT_COUNT=y
     combination
   - Limit PREEMPT_RCU configurations
   - Make rcutorture senario TREE07 and senario TREE10 use
     PREEMPT_LAZY=y"

* tag 'rcu-next-v6.15' of git://git.kernel.org/pub/scm/linux/kernel/git/rcu/linux: (59 commits)
  rcutorture: Make scenario TREE07 build CONFIG_PREEMPT_LAZY=y
  rcutorture: Make scenario TREE10 build CONFIG_PREEMPT_LAZY=y
  rcu: limit PREEMPT_RCU configurations
  rcutorture: Update ->extendables check for lazy preemption
  rcutorture: Update rcutorture_one_extend_check() for lazy preemption
  osnoise: provide quiescent states
  rcu: Use _full() API to debug synchronize_rcu()
  rcu: Update TREE05.boot to test normal synchronize_rcu()
  rcutorture: Allow a negative value for nfakewriters
  Flush console log from kernel_power_off()
  context_tracking: Make RCU watch ct_kernel_exit_state() warning
  rcu/nocb: Print segment lengths in show_rcu_nocb_gp_state()
  rcu-tasks: Move RCU Tasks self-tests to core_initcall()
  rcu: Fix get_state_synchronize_rcu_full() GP-start detection
  torture: Make SRCU lockdep testing use srcu_read_lock_nmisafe()
  srcu: Add FORCE_NEED_SRCU_NMI_SAFE Kconfig for testing
  rcutorture: Complain when invalid SRCU reader_flavor is specified
  rcutorture: Move RCU_TORTURE_TEST_{CHK_RDR_STATE,LOG_CPU} to bool
  rcutorture: Make cur_ops->format_gp_seqs take buffer length
  rcutorture: Add ftrace-compatible timestamp to GP# failure/close-call output
  ...
parents 2f2d5294 467c890f

Documentation/RCU/rcubarrier.rst

+1 −4
Original line number Diff line number Diff line
@@ -329,10 +329,7 @@ Answer: 
	was first added back in 2005.  This is because on_each_cpu()

	disables preemption, which acted as an RCU read-side critical

	section, thus preventing CPU 0's grace period from completing

	until on_each_cpu() had dealt with all of the CPUs.  However,

	with the advent of preemptible RCU, rcu_barrier() no longer

	waited on nonpreemptible regions of code in preemptible kernels,

	that being the job of the new rcu_barrier_sched() function.

	until on_each_cpu() had dealt with all of the CPUs.



	However, with the RCU flavor consolidation around v4.20, this

	possibility was once again ruled out, because the consolidated

Documentation/RCU/stallwarn.rst

+7 −0
Original line number Diff line number Diff line
@@ -96,6 +96,13 @@ warnings: 
	the ``rcu_.*timer wakeup didn't happen for`` console-log message,

	which will include additional debugging information.



-	A timer issue causes time to appear to jump forward, so that RCU

	believes that the RCU CPU stall-warning timeout has been exceeded

	when in fact much less time has passed.  This could be due to

	timer hardware bugs, timer driver bugs, or even corruption of

	the "jiffies" global variable.	These sorts of timer hardware

	and driver bugs are not uncommon when testing new hardware.



-	A low-level kernel issue that either fails to invoke one of the

	variants of rcu_eqs_enter(true), rcu_eqs_exit(true), ct_idle_enter(),

	ct_idle_exit(), ct_irq_enter(), or ct_irq_exit() on the one

Documentation/admin-guide/kernel-parameters.txt

+5 −0
Original line number Diff line number Diff line
@@ -5760,6 +5760,11 @@ 
	rcutorture.test_boost_duration= [KNL]

			Duration (s) of each individual boost test.



	rcutorture.test_boost_holdoff= [KNL]

			Holdoff time (s) from start of test to the start

			of RCU priority-boost testing.	Defaults to zero,

			that is, no holdoff.



	rcutorture.test_boost_interval= [KNL]

			Interval (s) between each boost test.

Documentation/core-api/this_cpu_ops.rst

+16 −6
Original line number Diff line number Diff line
@@ -138,12 +138,22 @@ get_cpu/put_cpu sequence requires. No processor number is 
available. Instead, the offset of the local per cpu area is simply

added to the per cpu offset.



Note that this operation is usually used in a code segment when

preemption has been disabled. The pointer is then used to

access local per cpu data in a critical section. When preemption

is re-enabled this pointer is usually no longer useful since it may

no longer point to per cpu data of the current processor.



Note that this operation can only be used in code segments where

smp_processor_id() may be used, for example, where preemption has been

disabled. The pointer is then used to access local per cpu data in a

critical section. When preemption is re-enabled this pointer is usually

no longer useful since it may no longer point to per cpu data of the

current processor.



The special cases where it makes sense to obtain a per-CPU pointer in

preemptible code are addressed by raw_cpu_ptr(), but such use cases need

to handle cases where two different CPUs are accessing the same per cpu

variable, which might well be that of a third CPU.  These use cases are

typically performance optimizations.  For example, SRCU implements a pair

of counters as a pair of per-CPU variables, and rcu_read_lock_nmisafe()

uses raw_cpu_ptr() to get a pointer to some CPU's counter, and uses

atomic_inc_long() to handle migration between the raw_cpu_ptr() and

the atomic_inc_long().



Per cpu variables and offsets

-----------------------------

include/linux/printk.h

+6 −0
Original line number Diff line number Diff line
@@ -207,6 +207,7 @@ void printk_legacy_allow_panic_sync(void); 
extern bool nbcon_device_try_acquire(struct console *con);

extern void nbcon_device_release(struct console *con);

void nbcon_atomic_flush_unsafe(void);

bool pr_flush(int timeout_ms, bool reset_on_progress);

#else

static inline __printf(1, 0)

int vprintk(const char *s, va_list args)
@@ -315,6 +316,11 @@ static inline void nbcon_atomic_flush_unsafe(void) 
{

}



static inline bool pr_flush(int timeout_ms, bool reset_on_progress)

{

	return true;

}



#endif



bool this_cpu_in_panic(void);