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authorNeilBrown <neilb@suse.de>2014-07-07 15:16:04 +1000
committerIngo Molnar <mingo@kernel.org>2014-07-16 15:10:41 +0200
commitc1221321b7c25b53204447cff9949a6d5a7ddddc (patch)
treeb4dc6613ab838dcd71023f5f018306574fc2985a /include/linux/wait.h
parent743162013d40ca612b4cb53d3a200dff2d9ab26e (diff)
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>
Diffstat (limited to 'include/linux/wait.h')
-rw-r--r--include/linux/wait.h18
1 files changed, 10 insertions, 8 deletions
diff --git a/include/linux/wait.h b/include/linux/wait.h
index 73960ff09e56..6fb1ba5f9b2f 100644
--- a/include/linux/wait.h
+++ b/include/linux/wait.h
@@ -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;