linux.git/kernel/sched/wait_bit.c, branch v6.18.21

sched: Make clangd usable

2025-06-11T09:20:53+00:00

Due to the weird Makefile setup of sched the various files do not
compile as stand alone units. The new generation of editors are trying
to do just this -- mostly to offer fancy things like completions but
also better syntax highlighting and code navigation.

Specifically, I've been playing around with neovim and clangd.

Setting up clangd on the kernel source is a giant pain in the arse
(this really should be improved), but once you do manage, you run into
dumb stuff like the above.

Fix up the scheduler files to at least pretend to work.

Signed-off-by: Peter Zijlstra (Intel) 
Acked-by: Ingo Molnar 
Tested-by: Juri Lelli 
Link: https://lkml.kernel.org/r/20250523164348.GN39944@noisy.programming.kicks-ass.net

sched/wait: Remove unused bit_wait_io_timeout

2024-10-07T07:28:41+00:00

bit_wait_io_timeout has been unused since 2016's
commit 62906027091f ("mm: add PageWaiters indicating tasks are waiting for a page bit")

Remove it.

Signed-off-by: "Dr. David Alan Gilbert" 
Signed-off-by: Peter Zijlstra (Intel) 
Reviewed-by: Tim Chen 
Link: https://lore.kernel.org/r/20241001234016.231696-1-linux@treblig.org

sched: Document wait_var_event() family of functions and wake_up_var()

2024-10-07T07:28:38+00:00

wake_up_var(), wait_var_event() and related interfaces are not
documented but have important ordering requirements.  This patch adds
documentation and makes these requirements explicit.

The return values for those wait_var_event_* functions which return a
value are documented.  Note that these are, perhaps surprisingly,
sometimes different from comparable wait_on_bit() functions.

Signed-off-by: NeilBrown 
Signed-off-by: Peter Zijlstra (Intel) 
Link: https://lore.kernel.org/r/20240925053405.3960701-4-neilb@suse.de

sched: Improve documentation for wake_up_bit/wait_on_bit family of functions

2024-10-07T07:28:37+00:00

This patch revises the documention for wake_up_bit(),
clear_and_wake_up_bit(), and all the wait_on_bit() family of functions.

The new documentation places less emphasis on the pool of waitqueues
used (an implementation detail) and focuses instead on details of how
the functions behave.

The barriers included in the wait functions and clear_and_wake_up_bit()
and those required for wake_up_bit() are spelled out more clearly.

The error statuses returned are given explicitly.

The fact that the wait_on_bit_lock() function sets the bit is made more
obvious.

Signed-off-by: NeilBrown 
Signed-off-by: Peter Zijlstra (Intel) 
Link: https://lore.kernel.org/r/20240925053405.3960701-3-neilb@suse.de

sched: change wake_up_bit() and related function to expect unsigned long *

2024-10-07T07:28:37+00:00

wake_up_bit() currently allows a "void *".  While this isn't strictly a
problem as the address is never dereferenced, it is inconsistent with
the corresponding wait_on_bit() which requires "unsigned long *" and
does dereference the pointer.

Any code that needs to wait for a change in something other than an
unsigned long would be better served by wake_up_var()/wait_var_event().

This patch changes all related "void *" to "unsigned long *".

Reported-by: Linus Torvalds 
Signed-off-by: NeilBrown 
Signed-off-by: Peter Zijlstra (Intel) 
Link: https://lore.kernel.org/r/20240925053405.3960701-2-neilb@suse.de

sched: Fix spelling in comments

2024-05-27T15:00:21+00:00

Do a spell-checking pass.

Signed-off-by: Ingo Molnar 
Cc: Peter Zijlstra 
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar

wait_on_bit: add an acquire memory barrier

2022-08-26T16:30:25+00:00

There are several places in the kernel where wait_on_bit is not followed
by a memory barrier (for example, in drivers/md/dm-bufio.c:new_read).

On architectures with weak memory ordering, it may happen that memory
accesses that follow wait_on_bit are reordered before wait_on_bit and
they may return invalid data.

Fix this class of bugs by introducing a new function "test_bit_acquire"
that works like test_bit, but has acquire memory ordering semantics.

Signed-off-by: Mikulas Patocka 
Acked-by: Will Deacon 
Cc: stable@vger.kernel.org
Signed-off-by: Linus Torvalds

sched/headers: Introduce kernel/sched/build_utility.c and build multiple .c files there

2022-02-23T09:58:33+00:00

Collect all utility functionality source code files into a single kernel/sched/build_utility.c file,
via #include-ing the .c files:

    kernel/sched/clock.c
    kernel/sched/completion.c
    kernel/sched/loadavg.c
    kernel/sched/swait.c
    kernel/sched/wait_bit.c
    kernel/sched/wait.c

CONFIG_CPU_FREQ:
    kernel/sched/cpufreq.c

CONFIG_CPU_FREQ_GOV_SCHEDUTIL:
    kernel/sched/cpufreq_schedutil.c

CONFIG_CGROUP_CPUACCT:
    kernel/sched/cpuacct.c

CONFIG_SCHED_DEBUG:
    kernel/sched/debug.c

CONFIG_SCHEDSTATS:
    kernel/sched/stats.c

CONFIG_SMP:
   kernel/sched/cpupri.c
   kernel/sched/stop_task.c
   kernel/sched/topology.c

CONFIG_SCHED_CORE:
   kernel/sched/core_sched.c

CONFIG_PSI:
   kernel/sched/psi.c

CONFIG_MEMBARRIER:
   kernel/sched/membarrier.c

CONFIG_CPU_ISOLATION:
   kernel/sched/isolation.c

CONFIG_SCHED_AUTOGROUP:
   kernel/sched/autogroup.c

The goal is to amortize the 60+ KLOC header bloat from over a dozen build units into
a single build unit.

The build time of build_utility.c also roughly matches the build time of core.c and
fair.c - allowing better load-balancing of scheduler-only rebuilds.

Signed-off-by: Ingo Molnar 
Reviewed-by: Peter Zijlstra

sched/wait: fix ___wait_var_event(exclusive)

2019-12-17T12:32:50+00:00

init_wait_var_entry() forgets to initialize wq_entry->flags.

Currently not a problem, we don't have wait_var_event_exclusive().

Signed-off-by: Oleg Nesterov 
Signed-off-by: Peter Zijlstra (Intel) 
Cc: Vincent Guittot 
Cc: Ingo Molnar 
Cc: Felipe Balbi 
Cc: Linus Torvalds 
Cc: Miklos Szeredi 
Cc: Juri Lelli 
Link: https://lkml.kernel.org/r/20191210191902.GB14449@redhat.com

treewide: Add SPDX license identifier for missed files

2019-05-21T08:50:45+00:00

Add SPDX license identifiers to all files which:

 - Have no license information of any form

 - Have EXPORT_.*_SYMBOL_GPL inside which was used in the
   initial scan/conversion to ignore the file

These files fall under the project license, GPL v2 only. The resulting SPDX
license identifier is:

  GPL-2.0-only

Signed-off-by: Thomas Gleixner 
Signed-off-by: Greg Kroah-Hartman