poll: allow f_op->poll to sleep

[Fwd to Andrew, CC fsdevel & Arjan]

Andrew, can you please apply this? I don't think it should be sneaked in through the fuse tree (even though the immediate requirement is from the poll implementation in fuse).

Thanks,
Miklos
----

From: Tejun Heo <[email protected]>

f_op->poll is the only vfs operation which is not allowed to sleep. It's because poll and select implementation used task state to synchronize against wake ups, which doesn't have to be the case anymore as wait/wake interface can now use custom wake up functions. The non-sleep restriction can be a bit tricky because ->poll is not called from an atomic context and the result of accidentally sleeping in ->poll only shows up as temporary busy looping when the timing is right or rather wrong.

This patch converts poll/select to use custom wake up function and use separate triggered variable to synchronize against wake up events. The only added overhead is an extra function call during wake up and negligible.

This patch removes the one non-sleep exception from vfs locking rules and is beneficial to userland filesystem implementations like FUSE, 9p or peculiar fs like spufs as it's very difficult for those to implement non-sleeping poll method.

While at it, make the following cosmetic changes to make poll.h and select.c checkpatch friendly.

* s/type * symbol/type *symbol/ : three places in poll.h
* remove blank line before EXPORT_SYMBOL() : two places in select.c

---
 Documentation/filesystems/Locking |    2 -
 drivers/media/video/v4l1-compat.c |    4 --
 fs/select.c                       |   51 +++++++++++++++++++++++++++-----------
 include/linux/poll.h              |   15 ++++++++---
 4 files changed, 51 insertions(+), 21 deletions(-)

Index: work/fs/select.c
===================================================================
@@ -109,11 +109,11 @@ static void __pollwait(struct file *filp
 void poll_initwait(struct poll_wqueues *pwq)
 {
 	init_poll_funcptr(&pwq->pt, __pollwait);
+	pwq->polling_task = current;
 	pwq->error = 0;
 	pwq->table = NULL;
 	pwq->inline_index = 0;
 }
-
 EXPORT_SYMBOL(poll_initwait);
 
 static void free_poll_entry(struct poll_table_entry *entry)

@@ -142,12 +142,10 @@ void poll_freewait(struct poll_wqueues *
 		free_page((unsigned long) old);
 	}
 }
-
 EXPORT_SYMBOL(poll_freewait);
 
-static struct poll_table_entry *poll_get_entry(poll_table *_p)
+static struct poll_table_entry *poll_get_entry(struct poll_wqueues *p)
 {
-	struct poll_wqueues *p = container_of(_p, struct poll_wqueues, pt);
 	struct poll_table_page *table = p->table;
 
 	if (p->inline_index < N_INLINE_POLL_ENTRIES)

@@ -159,7 +157,6 @@ static struct poll_table_entry *poll_get
 		new_table = (struct poll_table_page *) __get_free_page(GFP_KERNEL);
 		if (!new_table) {
 			p->error = -ENOMEM;
-			__set_current_state(TASK_RUNNING);
 			return NULL;
 		}
 		new_table->entry = new_table->entries;

@@ -171,20 +168,50 @@ static struct poll_table_entry *poll_get
 	return table->entry++;
 }
 
+static int pollwake(wait_queue_t *wait, unsigned mode, int sync, void *key)
+{
+	struct poll_wqueues *pwq = wait->private;
+	DECLARE_WAITQUEUE(dummy_wait, pwq->polling_task);
+
+	set_mb(pwq->triggered, 1);
+
+	/* perform the default wake up operation */
+	return default_wake_function(&dummy_wait, mode, sync, key);
+}
+
 /* Add a new entry */
 static void __pollwait(struct file *filp, wait_queue_head_t *wait_address,
 				poll_table *p)
 {
-	struct poll_table_entry *entry = poll_get_entry(p);
+	struct poll_wqueues *pwq = container_of(p, struct poll_wqueues, pt);
+	struct poll_table_entry *entry = poll_get_entry(pwq);
 	if (!entry)
 		return;
 	get_file(filp);
 	entry->filp = filp;
 	entry->wait_address = wait_address;
-	init_waitqueue_entry(&entry->wait, current);
+	init_waitqueue_func_entry(&entry->wait, pollwake);
+	entry->wait.private = pwq;
 	add_wait_queue(wait_address, &entry->wait);
 }
 
+int poll_schedule_timeout(struct poll_wqueues *pwq, int state,
+			  ktime_t *expires, unsigned long slack)
+{
+	int rc = -EINTR;
+
+	set_current_state(state);
+	if (!pwq->triggered)
+		rc = schedule_hrtimeout_range(expires, slack, HRTIMER_MODE_ABS);
+	__set_current_state(TASK_RUNNING);
+
+	/* clear triggered for the next iteration */
+	pwq->triggered = 0;
+
+	return rc;
+}
+EXPORT_SYMBOL(poll_schedule_timeout);
+
 /**
  * poll_select_set_timeout - helper function to setup the timeout value
  * @to:		pointer to timespec variable for the final timeout

@@ -340,8 +367,6 @@ int do_select(int n, fd_set_bits *fds, s
 	for (;;) {
 		unsigned long *rinp, *routp, *rexp, *inp, *outp, *exp;
 
-		set_current_state(TASK_INTERRUPTIBLE);
-
 		inp = fds->in; outp = fds->out; exp = fds->ex;
 		rinp = fds->res_in; routp = fds->res_out; rexp = fds->res_ex;
 

@@ -411,10 +436,10 @@ int do_select(int n, fd_set_bits *fds, s
 			to = &expire;
 		}
 
-		if (!schedule_hrtimeout_range(to, slack, HRTIMER_MODE_ABS))
+		if (!poll_schedule_timeout(&table, TASK_INTERRUPTIBLE,
+					   to, slack))
 			timed_out = 1;
 	}
-	__set_current_state(TASK_RUNNING);
 
 	poll_freewait(&table);
 

@@ -666,7 +691,6 @@ static int do_poll(unsigned int nfds,  s
 	for (;;) {
 		struct poll_list *walk;
 
-		set_current_state(TASK_INTERRUPTIBLE);
 		for (walk = list; walk != NULL; walk = walk->next) {
 			struct pollfd * pfd, * pfd_end;
 

@@ -709,10 +733,9 @@ static int do_poll(unsigned int nfds,  s
 			to = &expire;
 		}
 
-		if (!schedule_hrtimeout_range(to, slack, HRTIMER_MODE_ABS))
+		if (!poll_schedule_timeout(wait, TASK_INTERRUPTIBLE, to, slack))
 			timed_out = 1;
 	}
-	__set_current_state(TASK_RUNNING);
 	return count;
 }
 

Index: work/include/linux/poll.h
===================================================================
@@ -46,9 +46,9 @@ static inline void init_poll_funcptr(pol
 }
 
 struct poll_table_entry {
-	struct file * filp;
+	struct file *filp;
 	wait_queue_t wait;
-	wait_queue_head_t * wait_address;
+	wait_queue_head_t *wait_address;
 };
 
 /*

@@ -56,7 +56,9 @@ struct poll_table_entry {
  */
 struct poll_wqueues {
 	poll_table pt;
-	struct poll_table_page * table;
+	struct poll_table_page *table;
+	struct task_struct *polling_task;
+	int triggered;
 	int error;
 	int inline_index;
 	struct poll_table_entry inline_entries[N_INLINE_POLL_ENTRIES];

@@ -64,6 +66,13 @@ struct poll_wqueues {
 
 extern void poll_initwait(struct poll_wqueues *pwq);
 extern void poll_freewait(struct poll_wqueues *pwq);
+extern int poll_schedule_timeout(struct poll_wqueues *pwq, int state,
+				 ktime_t *expires, unsigned long slack);
+
+static inline int poll_schedule(struct poll_wqueues *pwq, int state)
+{
+	return poll_schedule_timeout(pwq, state, NULL, 0);
+}
 
 /*
  * Scaleable version of the fd_set.

Index: work/drivers/media/video/v4l1-compat.c
===================================================================
@@ -203,7 +203,6 @@ static int poll_one(struct file *file, s
 	table = &pwq->pt;
 	for (;;) {
 		int mask;
-		set_current_state(TASK_INTERRUPTIBLE);
 		mask = file->f_op->poll(file, table);
 		if (mask & POLLIN)
 			break;

@@ -212,9 +211,8 @@ static int poll_one(struct file *file, s
 			retval = -ERESTARTSYS;
 			break;
 		}
-		schedule();
+		poll_schedule(pwq, TASK_INTERRUPTIBLE);
 	}
-	set_current_state(TASK_RUNNING);
 	poll_freewait(pwq);
 	return retval;
 }

Index: work/Documentation/filesystems/Locking
===================================================================
@@ -398,7 +398,7 @@ prototypes:
 };
 
 locking rules:
-	All except ->poll() may block.
+	All may block.
 			BKL
 llseek:			no	(see below)
 read:			no

I did so earlier today.

Well, I wanted to keep it as to keep it more consistent with other schedule() functions but both Miklos and you don't seem to like it, so I might as well just drop it. Andrew, what do you think?

Thanks.

tejun

I guess that if any poll/select syscall were to sleep in uninterruptible state, people would get upset about the effect upon their load average and we'd have to go in and fix it.

So, yup, I expect that hard-coding TASK_INTERRUPTIBLE would be OK.

f_op->poll is the only vfs operation which is not allowed to sleep. It's because poll and select implementation used task state to synchronize against wake ups, which doesn't have to be the case anymore as wait/wake interface can now use custom wake up functions. The non-sleep restriction can be a bit tricky because ->poll is not called from an atomic context and the result of accidentally sleeping in ->poll only shows up as temporary busy looping when the timing is right or rather wrong.

This patch converts poll/select to use custom wake up function and use separate triggered variable to synchronize against wake up events. The only added overhead is an extra function call during wake up and negligible.

This patch removes the one non-sleep exception from vfs locking rules and is beneficial to userland filesystem implementations like FUSE, 9p or peculiar fs like spufs as it's very difficult for those to implement non-sleeping poll method.

---
@state dropped.

 Documentation/filesystems/Locking |    2 -
 drivers/media/video/v4l1-compat.c |    4 ---
 fs/select.c                       |   50 +++++++++++++++++++++++++++-----------
 include/linux/poll.h              |   15 +++++++++--
 4 files changed, 50 insertions(+), 21 deletions(-)

Index: work/fs/select.c
===================================================================
@@ -109,11 +109,11 @@ static void __pollwait(struct file *filp
 void poll_initwait(struct poll_wqueues *pwq)
 {
 	init_poll_funcptr(&pwq->pt, __pollwait);
+	pwq->polling_task = current;
 	pwq->error = 0;
 	pwq->table = NULL;
 	pwq->inline_index = 0;
 }
-
 EXPORT_SYMBOL(poll_initwait);
 
 static void free_poll_entry(struct poll_table_entry *entry)

@@ -142,12 +142,10 @@ void poll_freewait(struct poll_wqueues *
 		free_page((unsigned long) old);
 	}
 }
-
 EXPORT_SYMBOL(poll_freewait);
 
-static struct poll_table_entry *poll_get_entry(poll_table *_p)
+static struct poll_table_entry *poll_get_entry(struct poll_wqueues *p)
 {
-	struct poll_wqueues *p = container_of(_p, struct poll_wqueues, pt);
 	struct poll_table_page *table = p->table;
 
 	if (p->inline_index < N_INLINE_POLL_ENTRIES)

@@ -159,7 +157,6 @@ static struct poll_table_entry *poll_get
 		new_table = (struct poll_table_page *) __get_free_page(GFP_KERNEL);
 		if (!new_table) {
 			p->error = -ENOMEM;
-			__set_current_state(TASK_RUNNING);
 			return NULL;
 		}
 		new_table->entry = new_table->entries;

@@ -171,20 +168,50 @@ static struct poll_table_entry *poll_get
 	return table->entry++;
 }
 
+static int pollwake(wait_queue_t *wait, unsigned mode, int sync, void *key)
+{
+	struct poll_wqueues *pwq = wait->private;
+	DECLARE_WAITQUEUE(dummy_wait, pwq->polling_task);
+
+	set_mb(pwq->triggered, 1);
+
+	/* perform the default wake up operation */
+	return default_wake_function(&dummy_wait, mode, sync, key);
+}
+
 /* Add a new entry */
 static void __pollwait(struct file *filp, wait_queue_head_t *wait_address,
 				poll_table *p)
 {
-	struct poll_table_entry *entry = poll_get_entry(p);
+	struct poll_wqueues *pwq = container_of(p, struct poll_wqueues, pt);
+	struct poll_table_entry *entry = poll_get_entry(pwq);
 	if (!entry)
 		return;
 	get_file(filp);
 	entry->filp = filp;
 	entry->wait_address = wait_address;
-	init_waitqueue_entry(&entry->wait, current);
+	init_waitqueue_func_entry(&entry->wait, pollwake);
+	entry->wait.private = pwq;
 	add_wait_queue(wait_address, &entry->wait);
 }
 
+int poll_schedule_timeout(struct poll_wqueues *pwq,
+			  ktime_t *expires, unsigned long slack)
+{
+	int rc = -EINTR;
+
+	set_current_state(TASK_INTERRUPTIBLE);
+	if (!pwq->triggered)
+		rc = schedule_hrtimeout_range(expires, slack, HRTIMER_MODE_ABS);
+	__set_current_state(TASK_RUNNING);
+
+	/* clear triggered for the next iteration */
+	pwq->triggered = 0;
+
+	return rc;
+}
+EXPORT_SYMBOL(poll_schedule_timeout);
+
 /**
  * poll_select_set_timeout - helper function to setup the timeout value
  * @to:		pointer to timespec variable for the final timeout

@@ -340,8 +367,6 @@ int do_select(int n, fd_set_bits *fds, s
 	for (;;) {
 		unsigned long *rinp, *routp, *rexp, *inp, *outp, *exp;
 
-		set_current_state(TASK_INTERRUPTIBLE);
-
 		inp = fds->in; outp = fds->out; exp = fds->ex;
 		rinp = fds->res_in; routp = fds->res_out; rexp = fds->res_ex;
 

@@ -411,10 +436,9 @@ int do_select(int n, fd_set_bits *fds, s
 			to = &expire;
 		}
 
-		if (!schedule_hrtimeout_range(to, slack, HRTIMER_MODE_ABS))
+		if (!poll_schedule_timeout(&table, to, slack))
 			timed_out = 1;
 	}
-	__set_current_state(TASK_RUNNING);
 
 	poll_freewait(&table);
 

@@ -666,7 +690,6 @@ static int do_poll(unsigned int nfds,  s
 	for (;;) {
 		struct poll_list *walk;
 
-		set_current_state(TASK_INTERRUPTIBLE);
 		for (walk = list; walk != NULL; walk = walk->next) {
 			struct pollfd * pfd, * pfd_end;
 

@@ -709,10 +732,9 @@ static int do_poll(unsigned int nfds,  s
 			to = &expire;
 		}
 
-		if (!schedule_hrtimeout_range(to, slack, HRTIMER_MODE_ABS))
+		if (!poll_schedule_timeout(wait, to, slack))
 			timed_out = 1;
 	}
-	__set_current_state(TASK_RUNNING);
 	return count;
 }
 

Index: work/include/linux/poll.h
===================================================================
@@ -46,9 +46,9 @@ static inline void init_poll_funcptr(pol
 }
 
 struct poll_table_entry {
-	struct file * filp;
+	struct file *filp;
 	wait_queue_t wait;
-	wait_queue_head_t * wait_address;
+	wait_queue_head_t *wait_address;
 };
 
 /*

@@ -56,7 +56,9 @@ struct poll_table_entry {
  */
 struct poll_wqueues {
 	poll_table pt;
-	struct poll_table_page * table;
+	struct poll_table_page *table;
+	struct task_struct *polling_task;
+	int triggered;
 	int error;
 	int inline_index;
 	struct poll_table_entry inline_entries[N_INLINE_POLL_ENTRIES];

@@ -64,6 +66,13 @@ struct poll_wqueues {
 
 extern void poll_initwait(struct poll_wqueues *pwq);
 extern void poll_freewait(struct poll_wqueues *pwq);
+extern int poll_schedule_timeout(struct poll_wqueues *pwq,
+				 ktime_t *expires, unsigned long slack);
+
+static inline int poll_schedule(struct poll_wqueues *pwq)
+{
+	return poll_schedule_timeout(pwq, NULL, 0);
+}
 
 /*
  * Scaleable version of the fd_set.

Index: work/drivers/media/video/v4l1-compat.c
===================================================================
@@ -203,7 +203,6 @@ static int poll_one(struct file *file, s
 	table = &pwq->pt;
 	for (;;) {
 		int mask;
-		set_current_state(TASK_INTERRUPTIBLE);
 		mask = file->f_op->poll(file, table);
 		if (mask & POLLIN)
 			break;

@@ -212,9 +211,8 @@ static int poll_one(struct file *file, s
 			retval = -ERESTARTSYS;
 			break;
 		}
-		schedule();
+		poll_schedule(pwq);
 	}
-	set_current_state(TASK_RUNNING);
 	poll_freewait(pwq);
 	return retval;
 }

Index: work/Documentation/filesystems/Locking
===================================================================
@@ -398,7 +398,7 @@ prototypes:
 };
 
 locking rules:
-	All except ->poll() may block.
+	All may block.
 			BKL
 llseek:			no	(see below)
 read:			no

I thought try_to_wake_up() was made static to avoid abuse but then again creating dummy waitqueue is an obvious abuse of waitqueue. What do other people think? I'll be happy to use try_to_wake_up() directly.

Thanks.

tejun

Do you need all the extra arguments? The function wake_up_process() is already a wrapper around try_to_wake_up() and is exported, but it doesn't have any arguments other than the task_struct and uses defaults for the other arguments. I'm not sure if anything in your code would break by ignoring the other possible values instead of passing them along from the arguments into the caller.

Brad Boyer
[email protected]

Hmmm... there was something which made wake_up_process() inappropriate.
Ah, okay, it was @mode. We can add a WARN_ON() if @mode is an
unexpected value and use a fixed one - TASK_INTERRUPTIBLE or TASK_ALL - but that's even hackier than the waitqueue hack.

Thanks.

tejun

the already existing single-task-wakeup shortcut method made available by the scheduler is wake_up_process(). A number of primitives where waitqueue overhead is of concern already make use of it. (mutexes/rtmutexes and more)

if you need a different mode flag, then please extend the wake_up_process() family of APIs.

Ingo

Well, the problem is that for wait wake up functions @mode and @sync are passed as parameter and should be passed over to actual wake up function as-is, if I add @mode and @sync to wake_up_process() family of APIs, it's just try_to_wake_up().

Thanks.

tejun

_sync() is not something that should normally be done from poll handlers. But ->poll() handlers should all be TASK_INTERRUPTIBLE, right? So wake_up_process_interruptible() should be the thing you need?

Anyway, if you really want to pass in a state filter, you can use the already existing wake_up_state() method as well.

Ingo

It's not really about what I want but more about how the interface looks in the first place. Something like the following is simply ugly.

int my_callback(param a, param b, param c)

{
	WARN_ON(b != B);
	do_something(a);
}

And @sync might be useful depending on who's waking it up, so we either need to change the wake interface or give it an easier way to pass those parameters as received. The callback function isn't the right place to ignore those parameters. It simply doesn't know why the caller is passing them in or what they mean under the circumstances.

Thanks.

tejun

We'll likely eliminate the 'sync' parameter from the scheduler. It's not a flag that should be proliferated.

Ingo

But it's still being used in quite hot paths (pipe, splice, socket) and I don't really wanna mix up a change which can cause subtle scheduling related performance regression into this patch. How about using the dummy waitqueue hack for now and when removing the @sync param, switch it to one of wakeup APIs? I'll be happy to add big /* TODO */ comment in the function.

Thanks.

tejun

I was noticing that wake ups on the poll queues do not use sync=1, AFAICS. So using wake_up_state() and ignoring 'sync' should be fine. And 'key' is already ignored by default by default_wake_function().

- Davide

*cough* wrong *cough* :) Pipes & more.

- Davide

f_op->poll is the only vfs operation which is not allowed to sleep. It's because poll and select implementation used task state to synchronize against wake ups, which doesn't have to be the case anymore as wait/wake interface can now use custom wake up functions. The non-sleep restriction can be a bit tricky because ->poll is not called from an atomic context and the result of accidentally sleeping in ->poll only shows up as temporary busy looping when the timing is right or rather wrong.

This patch converts poll/select to use custom wake up function and use separate triggered variable to synchronize against wake up events. The only added overhead is an extra function call during wake up and negligible.

This patch removes the one non-sleep exception from vfs locking rules and is beneficial to userland filesystem implementations like FUSE, 9p or peculiar fs like spufs as it's very difficult for those to implement non-sleeping poll method.

While at it, make the following cosmetic changes to make poll.h and select.c checkpatch friendly.

* s/type * symbol/type *symbol/ : three places in poll.h
* remove blank line before EXPORT_SYMBOL() : two places in select.c

---
Added TODO comment to switch to wake_up_process() once @sync is gone.

Thanks.

 Documentation/filesystems/Locking |    2 -
 drivers/media/video/v4l1-compat.c |    4 --
 fs/select.c                       |   58
++++++++++++++++++++++++++++----------
 include/linux/poll.h              |   15 +++++++--
 4 files changed, 58 insertions(+), 21 deletions(-)

b/Documentation/filesystems/Locking
index 23d2f44..250f3c4 100644

@@ -398,7 +398,7 @@ prototypes:
 };
 
 locking rules:
-	All except ->poll() may block.
+	All may block.
 			BKL
 llseek:			no	(see below)
 read:			no

b/drivers/media/video/v4l1-compat.c
index f13c0a9..d0253da 100644

@@ -203,7 +203,6 @@ static int poll_one(struct file *file, struct

poll_wqueues *pwq)
table = &pwq->pt;
for (;;) {
int mask;
- set_current_state(TASK_INTERRUPTIBLE);
mask = file->f_op->poll(file, table); if (mask & POLLIN)
break;
@@ -212,9 +211,8 @@ static int poll_one(struct file *file, struct poll_wqueues *pwq)
retval = -ERESTARTSYS;
break;
}
- schedule();
+ poll_schedule(pwq, TASK_INTERRUPTIBLE);
}
- set_current_state(TASK_RUNNING);
poll_freewait(pwq);
return retval;
}

index 87df51e..f2ef68b 100644
@@ -109,11 +109,11 @@ static void __pollwait(struct file *filp,

wait_queue_head_t *wait_address,
void poll_initwait(struct poll_wqueues *pwq)
{
init_poll_funcptr(&pwq->pt, __pollwait);
+ pwq->polling_task = current;
pwq->error = 0;
pwq->table = NULL;
pwq->inline_index = 0;
}
-
EXPORT_SYMBOL(poll_initwait);

static void free_poll_entry(struct poll_table_entry *entry)
@@ -142,12 +142,10 @@ void poll_freewait(struct poll_wqueues *pwq)
free_page((unsigned long) old);
}
}
-
EXPORT_SYMBOL(poll_freewait);

-static struct poll_table_entry *poll_get_entry(poll_table *_p) +static struct poll_table_entry *poll_get_entry(struct poll_wqueues *p)
{
- struct poll_wqueues *p = container_of(_p, struct poll_wqueues, pt);
struct poll_table_page *table = p->table;

if (p->inline_index < N_INLINE_POLL_ENTRIES)
@@ -159,7 +157,6 @@ static struct poll_table_entry *poll_get_entry(poll_table *_p)
new_table = (struct poll_table_page *) __get_free_page(GFP_KERNEL); if (!new_table) {
p->error = -ENOMEM;
- __set_current_state(TASK_RUNNING);
return NULL;
}
new_table->entry = new_table->entries;
@@ -171,20 +168,57 @@ static struct poll_table_entry *poll_get_entry(poll_table *_p)
return table->entry++;
}

+static int pollwake(wait_queue_t *wait, unsigned mode, int sync, void *key) +{
+ struct poll_wqueues *pwq = wait->private;
+ DECLARE_WAITQUEUE(dummy_wait, pwq->polling_task);
+
+ set_mb(pwq->triggered, 1);
+
+ /*
+ * Perform the default wake up operation using a dummy
+ * waitqueue.
+ *
+ * TODO: This is hacky but there currently is no interface to
+ * pass in @sync. @sync is scheduled to be removed and once
+ * that happens, wake_up_process() can be used directly.
+ */
+ return default_wake_function(&dummy_wait, mode, sync, key);
+}
+
/* Add a new entry */
static void __pollwait(struct file *filp, wait_queue_head_t *wait_address,
poll_table *p)
{
- struct poll_table_entry *entry = poll_get_entry(p);
+ struct poll_wqueues *pwq = container_of(p, struct poll_wqueues, pt);
+ struct poll_table_entry *entry = poll_get_entry(pwq);
if (!entry)
return;
get_file(filp);
entry->filp = filp;
entry->wait_address = wait_address;
- init_waitqueue_entry(&entry->wait, current);
+ init_waitqueue_func_entry(&entry->wait, pollwake);
+ entry->wait.private = pwq;
add_wait_queue(wait_address, &entry->wait);
}

+int poll_schedule_timeout(struct poll_wqueues *pwq, int state,
+ ktime_t *expires, unsigned long slack)
+{
+ int rc = -EINTR;
+
+ set_current_state(state);
+ if (!pwq->triggered)
+ rc = schedule_hrtimeout_range(expires, slack, HRTIMER_MODE_ABS);
+ __set_current_state(TASK_RUNNING);
+
+ /* clear triggered for the next iteration */
+ pwq->triggered = 0;
+
+ return rc;
+}
+EXPORT_SYMBOL(poll_schedule_timeout);
+
/**
* poll_select_set_timeout - helper function to setup the timeout value
* @to: pointer to timespec variable for the final timeout
@@ -340,8 +374,6 @@ int do_select(int n, fd_set_bits *fds, struct timespec *end_time)
for (;;) {
unsigned long *rinp, *routp, *rexp, *inp, *outp, *exp;

- set_current_state(TASK_INTERRUPTIBLE);
-
inp = fds->in; outp = fds->out; exp = fds->ex; rinp = fds->res_in; routp = fds->res_out; rexp = fds->res_ex;

@@ -411,10 +443,10 @@ int do_select(int n, fd_set_bits *fds, struct timespec *end_time)
to = &expire;
}

- if (!schedule_hrtimeout_range(to, slack, HRTIMER_MODE_ABS))
+ if (!poll_schedule_timeout(&table, TASK_INTERRUPTIBLE,
+ to, slack))
timed_out = 1;
}
- __set_current_state(TASK_RUNNING);

poll_freewait(&table);

@@ -666,7 +698,6 @@ static int do_poll(unsigned int nfds, struct poll_list *list,
for (;;) {
struct poll_list *walk;

- set_current_state(TASK_INTERRUPTIBLE);
for (walk = list; walk != NULL; walk = walk->next) {
struct pollfd * pfd, * pfd_end;

@@ -709,10 +740,9 @@ static int do_poll(unsigned int nfds, struct poll_list *list,
to = &expire;
}

- if (!schedule_hrtimeout_range(to, slack, HRTIMER_MODE_ABS))
+ if (!poll_schedule_timeout(wait, TASK_INTERRUPTIBLE, to, slack))
timed_out = 1;
}
- __set_current_state(TASK_RUNNING);
return count;
}

index badd98a..8c24ef8 100644
@@ -46,9 +46,9 @@ static inline void init_poll_funcptr(poll_table *pt,

poll_queue_proc qproc)
}

struct poll_table_entry {
- struct file * filp;
+ struct file *filp;
wait_queue_t wait;
- wait_queue_head_t * wait_address;
+ wait_queue_head_t *wait_address;
};

/*
@@ -56,7 +56,9 @@ struct poll_table_entry {
*/
struct poll_wqueues {
poll_table pt;
- struct poll_table_page * table;
+ struct poll_table_page *table;
+ struct task_struct *polling_task;
+ int triggered;
int error;
int inline_index;
struct poll_table_entry inline_entries[N_INLINE_POLL_ENTRIES];
@@ -64,6 +66,13 @@ struct poll_wqueues {

extern void poll_initwait(struct poll_wqueues *pwq); extern void poll_freewait(struct poll_wqueues *pwq);
+extern int poll_schedule_timeout(struct poll_wqueues *pwq, int state,
+ ktime_t *expires, unsigned long slack);
+
+static inline int poll_schedule(struct poll_wqueues *pwq, int state) +{
+ return poll_schedule_timeout(pwq, state, NULL, 0);
+}

/*
* Scaleable version of the fd_set.