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Neeraj Upadhyay 0fda786242 rcu-tasks: Fix IPI failure handling in trc_wait_for_one_reader
commit 46aa886c48 upstream.

The trc_wait_for_one_reader() function is called at multiple stages
of trace rcu-tasks GP function, rcu_tasks_wait_gp():

- First, it is called as part of per task function -
  rcu_tasks_trace_pertask(), for all non-idle tasks. As part of per task
  processing, this function add the task in the holdout list and if the
  task is currently running on a CPU, it sends IPI to the task's CPU.
  The IPI handler takes action depending on whether task is in trace
  rcu-tasks read side critical section or not:

  - a. If the task is in trace rcu-tasks read side critical section
       (t->trc_reader_nesting != 0), the IPI handler sets the task's
       ->trc_reader_special.b.need_qs, so that this task notifies exit
       from its outermost read side critical section (by decrementing
       trc_n_readers_need_end) to the GP handling function.
       trc_wait_for_one_reader() also increments trc_n_readers_need_end,
       so that the trace rcu-tasks GP handler function waits for this
       task's read side exit notification. The IPI handler also sets
       t->trc_reader_checked to true, and no further IPIs are sent for
       this task, for this trace rcu-tasks grace period and this
       task can be removed from holdout list.

  - b. If the task is in the process of exiting its trace rcu-tasks
       read side critical section, (t->trc_reader_nesting < 0), defer
       this task's processing to future calls to trc_wait_for_one_reader().

  - c. If task is not in rcu-task read side critical section,
       t->trc_reader_nesting == 0, ->trc_reader_checked is set for this
       task, so that this task is removed from holdout list.

- Second, trc_wait_for_one_reader() is called as part of post scan, in
  function rcu_tasks_trace_postscan(), for all idle tasks.

- Third, in function check_all_holdout_tasks_trace(), this function is
  called for each task in the holdout list, but only if there isn't
  a pending IPI for the task (->trc_ipi_to_cpu == -1). This function
  removed the task from holdout list, if IPI handler has completed the
  required work, to ensure that the current trace rcu-tasks grace period
  either waits for this task, or this task is not in a trace rcu-tasks
  read side critical section.

Now, considering the scenario where smp_call_function_single() fails in
first case, inside rcu_tasks_trace_pertask(). In this case,
->trc_ipi_to_cpu is set to the current CPU for that task. This will
result in trc_wait_for_one_reader() getting skipped in third case,
inside check_all_holdout_tasks_trace(), for this task. This further
results in ->trc_reader_checked never getting set for this task,
and the task not getting removed from holdout list. This can cause
the current trace rcu-tasks grace period to stall.

Fix the above problem, by resetting ->trc_ipi_to_cpu to -1, on
smp_call_function_single() failure, so that future IPI calls can
be send for this task.

Note that all three of the trc_wait_for_one_reader() function's
callers (rcu_tasks_trace_pertask(), rcu_tasks_trace_postscan(),
check_all_holdout_tasks_trace()) hold cpu_read_lock().  This means
that smp_call_function_single() cannot race with CPU hotplug, and thus
should never fail.  Therefore, also add a warning in order to report
any such failure in case smp_call_function_single() grows some other
reason for failure.

Signed-off-by: Neeraj Upadhyay <neeraju@codeaurora.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Cc: Joel Fernandes <joel@joelfernandes.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2023-09-05 01:25:15 +08:00
arch ARM: module: Use module_init_layout_section() to spot init sections 2023-09-05 01:25:15 +08:00
block block/partition: fix signedness issue for Amiga partitions 2023-08-20 15:24:51 +08:00
certs certs/blacklist_hashes.c: fix const confusion in certs blacklist 2023-04-19 17:50:34 +08:00
crypto KEYS: asymmetric: Copy sig and digest in public_key_verify_signature() 2023-08-20 15:21:12 +08:00
Documentation ACPI: thermal: Drop nocrt parameter 2023-09-05 01:25:15 +08:00
drivers ACPI: thermal: Drop nocrt parameter 2023-09-05 01:25:15 +08:00
fs nfsd: use vfs setgid helper 2023-09-05 01:25:10 +08:00
include module: Expose module_init_layout_section() 2023-09-05 01:25:15 +08:00
init x86/mm: Initialize text poking earlier 2023-08-20 16:01:29 +08:00
io_uring io_uring: correct check for O_TMPFILE 2023-08-20 16:01:40 +08:00
ipc ipc/sem: Fix dangling sem_array access in semtimedop race 2023-04-19 17:56:54 +08:00
kernel rcu-tasks: Fix IPI failure handling in trc_wait_for_one_reader 2023-09-05 01:25:15 +08:00
lib radix tree: remove unused variable 2023-09-05 01:25:09 +08:00
LICENSES LICENSES/dual/CC-BY-4.0: Git rid of "smart quotes" 2021-07-15 06:31:24 -06:00
mm mm: memory-failure: fix unexpected return value in soft_offline_page() 2023-09-05 01:25:11 +08:00
net can: raw: add missing refcount for memory leak fix 2023-09-05 01:25:11 +08:00
samples samples: ftrace: Save required argument registers in sample trampolines 2023-08-20 16:01:05 +08:00
scripts kbuild: Disable GCOV for *.mod.o 2023-08-20 15:24:38 +08:00
security selinux: set next pointer before attaching to list 2023-09-05 01:25:08 +08:00
sound ALSA: ymfpci: Fix the missing snd_card_free() call at probe error 2023-09-05 01:25:07 +08:00
tools objtool/x86: Fix SRSO mess 2023-09-05 01:25:02 +08:00
usr usr/include/Makefile: add linux/nfc.h to the compile-test coverage 2023-04-19 17:44:58 +08:00
virt KVM: Grab a reference to KVM for VM and vCPU stats file descriptors 2023-08-20 16:01:23 +08:00
.clang-format clang-format: Update with the latest for_each macro list 2021-05-12 23:32:39 +02:00
.cocciconfig
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COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
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Kbuild kbuild: rename hostprogs-y/always to hostprogs/always-y 2020-02-04 01:53:07 +09:00
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stfsync.txt add file to track last rebase commit from stf 2023-08-21 00:12:49 +08:00

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.