sched: Allow wait_on_bit_action() functions to support a timeout

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>

1 files changed, 8 insertions, 8 deletions

diff --git a/kernel/sched/wait.c b/kernel/sched/wait.c
index a104879e88f2..15cab1a4f84e 100644
--- a/kernel/sched/wait.c
+++ b/kernel/sched/wait.c
@@ -319,14 +319,14 @@ EXPORT_SYMBOL(wake_bit_function);
  */
 int __sched
 __wait_on_bit(wait_queue_head_t *wq, struct wait_bit_queue *q,
-                        int (*action)(void *), unsigned mode)
+              wait_bit_action_f *action, unsigned mode)
 {
         int ret = 0;
 
         do {
                 prepare_to_wait(wq, &q->wait, mode);
                 if (test_bit(q->key.bit_nr, q->key.flags))
-                        ret = (*action)(q->key.flags);
+                        ret = (*action)(&q->key);
         } while (test_bit(q->key.bit_nr, q->key.flags) && !ret);
         finish_wait(wq, &q->wait);
         return ret;
@@ -334,7 +334,7 @@ __wait_on_bit(wait_queue_head_t *wq, struct wait_bit_queue *q,
 EXPORT_SYMBOL(__wait_on_bit);
 
 int __sched out_of_line_wait_on_bit(void *word, int bit,
-                                        int (*action)(void *), unsigned mode)
+                                    wait_bit_action_f *action, unsigned mode)
 {
         wait_queue_head_t *wq = bit_waitqueue(word, bit);
         DEFINE_WAIT_BIT(wait, word, bit);
@@ -345,7 +345,7 @@ EXPORT_SYMBOL(out_of_line_wait_on_bit);
 
 int __sched
 __wait_on_bit_lock(wait_queue_head_t *wq, struct wait_bit_queue *q,
-                        int (*action)(void *), unsigned mode)
+                        wait_bit_action_f *action, unsigned mode)
 {
         do {
                 int ret;
@@ -353,7 +353,7 @@ __wait_on_bit_lock(wait_queue_head_t *wq, struct wait_bit_queue *q,
                 prepare_to_wait_exclusive(wq, &q->wait, mode);
                 if (!test_bit(q->key.bit_nr, q->key.flags))
                         continue;
-                ret = action(q->key.flags);
+                ret = action(&q->key);
                 if (!ret)
                         continue;
                 abort_exclusive_wait(wq, &q->wait, mode, &q->key);
@@ -365,7 +365,7 @@ __wait_on_bit_lock(wait_queue_head_t *wq, struct wait_bit_queue *q,
 EXPORT_SYMBOL(__wait_on_bit_lock);
 
 int __sched out_of_line_wait_on_bit_lock(void *word, int bit,
-                                        int (*action)(void *), unsigned mode)
+                                         wait_bit_action_f *action, unsigned mode)
 {
         wait_queue_head_t *wq = bit_waitqueue(word, bit);
         DEFINE_WAIT_BIT(wait, word, bit);
@@ -503,7 +503,7 @@ void wake_up_atomic_t(atomic_t *p)
 }
 EXPORT_SYMBOL(wake_up_atomic_t);
 
-__sched int bit_wait(void *word)
+__sched int bit_wait(struct wait_bit_key *word)
 {
         if (signal_pending_state(current->state, current))
                 return 1;
@@ -512,7 +512,7 @@ __sched int bit_wait(void *word)
 }
 EXPORT_SYMBOL(bit_wait);
 
-__sched int bit_wait_io(void *word)
+__sched int bit_wait_io(struct wait_bit_key *word)
 {
         if (signal_pending_state(current->state, current))
                 return 1;