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sched: Allow wait_on_bit_action() functions to support a timeout

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It is currently not possible for various wait_on_bit functions
to implement a timeout.

While the "action" function that is called to do the waiting
could certainly use schedule_timeout(), there is no way to carry
forward the remaining timeout after a false wake-up.
As false-wakeups a clearly possible at least due to possible
hash collisions in bit_waitqueue(), this is a real problem.

The 'action' function is currently passed a pointer to the word
containing the bit being waited on.  No current action functions
use this pointer.  So changing it to something else will be a
little noisy but will have no immediate effect.

This patch changes the 'action' function to take a pointer to
the "struct wait_bit_key", which contains a pointer to the word
containing the bit so nothing is really lost.

It also adds a 'private' field to "struct wait_bit_key", which
is initialized to zero.

An action function can now implement a timeout with something
like

static int timed_out_waiter(struct wait_bit_key *key)
{
	unsigned long waited;
	if (key->private == 0) {
		key->private = jiffies;
		if (key->private == 0)
			key->private -= 1;
	}
	waited = jiffies - key->private;
	if (waited > 10 * HZ)
		return -EAGAIN;
	schedule_timeout(waited - 10 * HZ);
	return 0;
}

If any other need for context in a waiter were found it would be
easy to use ->private for some other purpose, or even extend
"struct wait_bit_key".

My particular need is to support timeouts in nfs_release_page()
to avoid deadlocks with loopback mounted NFS.

While wait_on_bit_timeout() would be a cleaner interface, it
will not meet my need.  I need the timeout to be sensitive to
the state of the connection with the server, which could change.
 So I need to use an 'action' interface.

Signed-off-by: NeilBrown <neilb@suse.de>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Steve French <sfrench@samba.org>
Cc: David Howells <dhowells@redhat.com>
Cc: Steven Whitehouse <swhiteho@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/20140707051604.28027.41257.stgit@notabene.brown
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
NeilBrown 2014-07-07 15:16:04 +10:00 • committed by Ingo Molnar
parent 743162013d
commit c1221321b7
8 changed files with 25 additions and 23 deletions
Download patch file Download diff file Expand all files Collapse all files

18
include/linux/wait.h
View file

@ -25,6 +25,7 @@ struct wait_bit_key {
void *flags;
int bit_nr;
#define WAIT_ATOMIC_T_BIT_NR -1
unsigned long private;
};
struct wait_bit_queue {
@ -141,18 +142,19 @@ __remove_wait_queue(wait_queue_head_t *head, wait_queue_t *old)
list_del(&old->task_list);
}
typedef int wait_bit_action_f(struct wait_bit_key *);
void __wake_up(wait_queue_head_t *q, unsigned int mode, int nr, void *key);
void __wake_up_locked_key(wait_queue_head_t *q, unsigned int mode, void *key);
void __wake_up_sync_key(wait_queue_head_t *q, unsigned int mode, int nr, void *key);
void __wake_up_locked(wait_queue_head_t *q, unsigned int mode, int nr);
void __wake_up_sync(wait_queue_head_t *q, unsigned int mode, int nr);
void __wake_up_bit(wait_queue_head_t *, void *, int);
int __wait_on_bit(wait_queue_head_t *, struct wait_bit_queue *, int (*)(void *), unsigned);
int __wait_on_bit_lock(wait_queue_head_t *, struct wait_bit_queue *, int (*)(void *), unsigned);
int __wait_on_bit(wait_queue_head_t *, struct wait_bit_queue *, wait_bit_action_f *, unsigned);
int __wait_on_bit_lock(wait_queue_head_t *, struct wait_bit_queue *, wait_bit_action_f *, unsigned);
void wake_up_bit(void *, int);
void wake_up_atomic_t(atomic_t *);
int out_of_line_wait_on_bit(void *, int, int (*)(void *), unsigned);
int out_of_line_wait_on_bit_lock(void *, int, int (*)(void *), unsigned);
int out_of_line_wait_on_bit(void *, int, wait_bit_action_f *, unsigned);
int out_of_line_wait_on_bit_lock(void *, int, wait_bit_action_f *, unsigned);
int out_of_line_wait_on_atomic_t(atomic_t *, int (*)(atomic_t *), unsigned);
wait_queue_head_t *bit_waitqueue(void *, int);
@ -855,8 +857,8 @@ int wake_bit_function(wait_queue_t *wait, unsigned mode, int sync, void *key);
} while (0)
extern int bit_wait(void *);
extern int bit_wait_io(void *);
extern int bit_wait(struct wait_bit_key *);
extern int bit_wait_io(struct wait_bit_key *);
/**
* wait_on_bit - wait for a bit to be cleared
@ -925,7 +927,7 @@ wait_on_bit_io(void *word, int bit, unsigned mode)
* on that signal.
*/
static inline int
wait_on_bit_action(void *word, int bit, int (*action)(void *), unsigned mode)
wait_on_bit_action(void *word, int bit, wait_bit_action_f *action, unsigned mode)
{
if (!test_bit(bit, word))
return 0;
@ -1000,7 +1002,7 @@ wait_on_bit_lock_io(void *word, int bit, unsigned mode)
* the @mode allows that signal to wake the process.
*/
static inline int
wait_on_bit_lock_action(void *word, int bit, int (*action)(void *), unsigned mode)
wait_on_bit_lock_action(void *word, int bit, wait_bit_action_f *action, unsigned mode)
{
if (!test_and_set_bit(bit, word))
return 0;