mirror of
https://github.com/edk2-porting/linux-next.git
synced 2024-12-23 04:34:11 +08:00
a5c6234e10
completion uses a wait_queue_head_t to enqueue waiters.
wait_queue_head_t contains a spinlock_t to protect the list of waiters
which excludes it from being used in truly atomic context on a PREEMPT_RT
enabled kernel.
The spinlock in the wait queue head cannot be replaced by a raw_spinlock
because:
- wait queues can have custom wakeup callbacks, which acquire other
spinlock_t locks and have potentially long execution times
- wake_up() walks an unbounded number of list entries during the wake up
and may wake an unbounded number of waiters.
For simplicity and performance reasons complete() should be usable on
PREEMPT_RT enabled kernels.
completions do not use custom wakeup callbacks and are usually single
waiter, except for a few corner cases.
Replace the wait queue in the completion with a simple wait queue (swait),
which uses a raw_spinlock_t for protecting the waiter list and therefore is
safe to use inside truly atomic regions on PREEMPT_RT.
There is no semantical or functional change:
- completions use the exclusive wait mode which is what swait provides
- complete() wakes one exclusive waiter
- complete_all() wakes all waiters while holding the lock which protects
the wait queue against newly incoming waiters. The conversion to swait
preserves this behaviour.
complete_all() might cause unbound latencies with a large number of waiters
being woken at once, but most complete_all() usage sites are either in
testing or initialization code or have only a really small number of
concurrent waiters which for now does not cause a latency problem. Keep it
simple for now.
The fixup of the warning check in the USB gadget driver is just a straight
forward conversion of the lockless waiter check from one waitqueue type to
the other.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Davidlohr Bueso <dbueso@suse.de>
Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lkml.kernel.org/r/20200321113242.317954042@linutronix.de
122 lines
4.1 KiB
C
122 lines
4.1 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
|
|
#ifndef __LINUX_COMPLETION_H
|
|
#define __LINUX_COMPLETION_H
|
|
|
|
/*
|
|
* (C) Copyright 2001 Linus Torvalds
|
|
*
|
|
* Atomic wait-for-completion handler data structures.
|
|
* See kernel/sched/completion.c for details.
|
|
*/
|
|
|
|
#include <linux/swait.h>
|
|
|
|
/*
|
|
* struct completion - structure used to maintain state for a "completion"
|
|
*
|
|
* This is the opaque structure used to maintain the state for a "completion".
|
|
* Completions currently use a FIFO to queue threads that have to wait for
|
|
* the "completion" event.
|
|
*
|
|
* See also: complete(), wait_for_completion() (and friends _timeout,
|
|
* _interruptible, _interruptible_timeout, and _killable), init_completion(),
|
|
* reinit_completion(), and macros DECLARE_COMPLETION(),
|
|
* DECLARE_COMPLETION_ONSTACK().
|
|
*/
|
|
struct completion {
|
|
unsigned int done;
|
|
struct swait_queue_head wait;
|
|
};
|
|
|
|
#define init_completion_map(x, m) __init_completion(x)
|
|
#define init_completion(x) __init_completion(x)
|
|
static inline void complete_acquire(struct completion *x) {}
|
|
static inline void complete_release(struct completion *x) {}
|
|
|
|
#define COMPLETION_INITIALIZER(work) \
|
|
{ 0, __SWAIT_QUEUE_HEAD_INITIALIZER((work).wait) }
|
|
|
|
#define COMPLETION_INITIALIZER_ONSTACK_MAP(work, map) \
|
|
(*({ init_completion_map(&(work), &(map)); &(work); }))
|
|
|
|
#define COMPLETION_INITIALIZER_ONSTACK(work) \
|
|
(*({ init_completion(&work); &work; }))
|
|
|
|
/**
|
|
* DECLARE_COMPLETION - declare and initialize a completion structure
|
|
* @work: identifier for the completion structure
|
|
*
|
|
* This macro declares and initializes a completion structure. Generally used
|
|
* for static declarations. You should use the _ONSTACK variant for automatic
|
|
* variables.
|
|
*/
|
|
#define DECLARE_COMPLETION(work) \
|
|
struct completion work = COMPLETION_INITIALIZER(work)
|
|
|
|
/*
|
|
* Lockdep needs to run a non-constant initializer for on-stack
|
|
* completions - so we use the _ONSTACK() variant for those that
|
|
* are on the kernel stack:
|
|
*/
|
|
/**
|
|
* DECLARE_COMPLETION_ONSTACK - declare and initialize a completion structure
|
|
* @work: identifier for the completion structure
|
|
*
|
|
* This macro declares and initializes a completion structure on the kernel
|
|
* stack.
|
|
*/
|
|
#ifdef CONFIG_LOCKDEP
|
|
# define DECLARE_COMPLETION_ONSTACK(work) \
|
|
struct completion work = COMPLETION_INITIALIZER_ONSTACK(work)
|
|
# define DECLARE_COMPLETION_ONSTACK_MAP(work, map) \
|
|
struct completion work = COMPLETION_INITIALIZER_ONSTACK_MAP(work, map)
|
|
#else
|
|
# define DECLARE_COMPLETION_ONSTACK(work) DECLARE_COMPLETION(work)
|
|
# define DECLARE_COMPLETION_ONSTACK_MAP(work, map) DECLARE_COMPLETION(work)
|
|
#endif
|
|
|
|
/**
|
|
* init_completion - Initialize a dynamically allocated completion
|
|
* @x: pointer to completion structure that is to be initialized
|
|
*
|
|
* This inline function will initialize a dynamically created completion
|
|
* structure.
|
|
*/
|
|
static inline void __init_completion(struct completion *x)
|
|
{
|
|
x->done = 0;
|
|
init_swait_queue_head(&x->wait);
|
|
}
|
|
|
|
/**
|
|
* reinit_completion - reinitialize a completion structure
|
|
* @x: pointer to completion structure that is to be reinitialized
|
|
*
|
|
* This inline function should be used to reinitialize a completion structure so it can
|
|
* be reused. This is especially important after complete_all() is used.
|
|
*/
|
|
static inline void reinit_completion(struct completion *x)
|
|
{
|
|
x->done = 0;
|
|
}
|
|
|
|
extern void wait_for_completion(struct completion *);
|
|
extern void wait_for_completion_io(struct completion *);
|
|
extern int wait_for_completion_interruptible(struct completion *x);
|
|
extern int wait_for_completion_killable(struct completion *x);
|
|
extern unsigned long wait_for_completion_timeout(struct completion *x,
|
|
unsigned long timeout);
|
|
extern unsigned long wait_for_completion_io_timeout(struct completion *x,
|
|
unsigned long timeout);
|
|
extern long wait_for_completion_interruptible_timeout(
|
|
struct completion *x, unsigned long timeout);
|
|
extern long wait_for_completion_killable_timeout(
|
|
struct completion *x, unsigned long timeout);
|
|
extern bool try_wait_for_completion(struct completion *x);
|
|
extern bool completion_done(struct completion *x);
|
|
|
|
extern void complete(struct completion *);
|
|
extern void complete_all(struct completion *);
|
|
|
|
#endif
|