linux.git/kernel/rcu/tree_stall.h, branch v5.8

Merge tag 'tty-5.8-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty

2020-06-07T16:52:36+00:00

Pull tty/serial driver updates from Greg KH:
 "Here is the tty and serial driver updates for 5.8-rc1

  Nothing huge at all, just a lot of little serial driver fixes, updates
  for new devices and features, and other small things. Full details are
  in the shortlog.

  All of these have been in linux-next with no issues for a while"

* tag 'tty-5.8-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty: (67 commits)
  tty: serial: qcom_geni_serial: Add 51.2MHz frequency support
  tty: serial: imx: clear Ageing Timer Interrupt in handler
  serial: 8250_fintek: Add F81966 Support
  sc16is7xx: Add flag to activate IrDA mode
  dt-bindings: sc16is7xx: Add flag to activate IrDA mode
  serial: 8250: Support rs485 bus termination GPIO
  serial: 8520_port: Fix function param documentation
  dt-bindings: serial: Add binding for rs485 bus termination GPIO
  vt: keyboard: avoid signed integer overflow in k_ascii
  serial: 8250: Enable 16550A variants by default on non-x86
  tty: hvc_console, fix crashes on parallel open/close
  serial: imx: Initialize lock for non-registered console
  sc16is7xx: Read the LSR register for basic device presence check
  sc16is7xx: Allow sharing the IRQ line
  sc16is7xx: Use threaded IRQ
  sc16is7xx: Always use falling edge IRQ
  tty: n_gsm: Fix bogus i++ in gsm_data_kick
  tty: n_gsm: Remove unnecessary test in gsm_print_packet()
  serial: stm32: add no_console_suspend support
  tty: serial: fsl_lpuart: Use __maybe_unused instead of #if CONFIG_PM_SLEEP
  ...

rcu: constify sysrq_key_op

2020-05-15T12:53:20+00:00

With earlier commits, the API no longer discards the const-ness of the
sysrq_key_op. As such we can add the notation.

Cc: Greg Kroah-Hartman 
Cc: Jiri Slaby 
Cc: linux-kernel@vger.kernel.org
Cc: "Paul E. McKenney" 
Cc: Josh Triplett 
Cc: rcu@vger.kernel.org
Reviewed-by: Paul E. McKenney 
Signed-off-by: Emil Velikov 
Link: https://lore.kernel.org/r/20200513214351.2138580-11-emil.l.velikov@gmail.com
Signed-off-by: Greg Kroah-Hartman

Merge branches 'fixes.2020.04.27a', 'kfree_rcu.2020.04.27a', 'rcu-tasks.2020.04.27a', 'stall.2020.04.27a' and 'torture.2020.05.07a' into HEAD

2020-05-07T17:18:32+00:00

fixes.2020.04.27a:  Miscellaneous fixes.
kfree_rcu.2020.04.27a:  Changes related to kfree_rcu().
rcu-tasks.2020.04.27a:  Addition of new RCU-tasks flavors.
stall.2020.04.27a:  RCU CPU stall-warning updates.
torture.2020.05.07a:  Torture-test updates.

rcu: Remove self-stack-trace when all quiescent states seen

2020-04-27T18:04:37+00:00

When all quiescent states have been seen, it is normally the grace-period
kthread that is in trouble.  Although the existing stack trace from
the current CPU might possibly provide useful information, experience
indicates that there is too much noise for this to be worthwhile.

This commit therefore removes this stack trace from the output.

Signed-off-by: Paul E. McKenney

rcu: When GP kthread is starved, tag idle threads as false positives

2020-04-27T18:04:37+00:00

If the grace-period kthread is starved, idle threads' extended quiescent
states are not reported.  These idle threads thus wrongly appear to
be blocking the current grace period.  This commit therefore tags such
idle threads as probable false positives when the grace-period kthread
is being starved.

Signed-off-by: Paul E. McKenney

rcu-tasks: Add RCU tasks to rcutorture writer stall output

2020-04-27T18:03:51+00:00

This commit adds state for each RCU-tasks flavor to the rcutorture
writer stall output.  The initial state is minimal, but you have to
start somewhere.

Signed-off-by: Paul E. McKenney 
[ paulmck: Fixes based on feedback from kbuild test robot. ]

rcu: Add per-task state to RCU CPU stall warnings

2020-04-27T18:03:50+00:00

Currently, an RCU-preempt CPU stall warning simply lists the PIDs of
those tasks holding up the current grace period.  This can be helpful,
but more can be even more helpful.

To this end, this commit adds the nesting level, whether the task
thinks it was preempted in its current RCU read-side critical section,
whether RCU core has asked this task for a quiescent state, whether the
expedited-grace-period hint is set, and whether the task believes that
it is on the blocked-tasks list (it must be, or it would not be printed,
but if things are broken, best not to take too much for granted).

Signed-off-by: Paul E. McKenney

rcu: Add rcu_gp_might_be_stalled()

2020-04-27T18:02:50+00:00

This commit adds rcu_gp_might_be_stalled(), which returns true if there
is some reason to believe that the RCU grace period is stalled.  The use
case is where an RCU free-memory path needs to allocate memory in order
to free it, a situation that should be avoided where possible.

But where it is necessary, there is always the alternative of using
synchronize_rcu() to wait for a grace period in order to avoid the
allocation.  And if the grace period is stalled, allocating memory to
asynchronously wait for it is a bad idea of epic proportions: Far better
to let others use the memory, because these others might actually be
able to free that memory before the grace period ends.

Thus, rcu_gp_might_be_stalled() can be used to help decide whether
allocating memory on an RCU free path is a semi-reasonable course
of action.

Cc: Joel Fernandes 
Cc: Uladzislau Rezki 
Signed-off-by: Paul E. McKenney

rcu: Fix the (t=0 jiffies) false positive

2020-04-27T18:01:16+00:00

It is possible that an over-long grace period will end while the RCU
CPU stall warning message is printing.  In this case, the estimate of
the offending grace period's duration can be erroneous due to refetching
of rcu_state.gp_start, which will now be the time of the newly started
grace period.  Computation of this duration clearly needs to use the
start time for the old over-long grace period, not the fresh new one.
This commit avoids such errors by causing both print_other_cpu_stall() and
print_cpu_stall() to reuse the value previously fetched by their caller.

Signed-off-by: Zhaolong Zhang 
Signed-off-by: Paul E. McKenney

rcu: Use data_race() for RCU CPU stall-warning prints

2020-04-27T18:01:16+00:00

Although the accesses used to determine whether or not a stall should
be printed are an integral part of the concurrency algorithm governing
use of the corresponding variables, the values that are simply printed
are ancillary.  As such, it is best to use data_race() for these accesses
in order to provide the greatest latitude in the use of KCSAN for the
other accesses that are an integral part of the algorithm.  This commit
therefore changes the relevant uses of READ_ONCE() to data_race().

Signed-off-by: Paul E. McKenney