On Wed, 2007-07-11 at 21:24 -0700, Andrew Morton wrote:
> We seem to be taking the reference against the wrong thing here. It should
> be against the mm, not against a task_struct?
This is solely for the wakeup: you don't wake an mm 8)
The mm reference is held as well under the big lguest_mutex (mm gets
destroyed before files get closed, so we definitely do need to hold a
reference).
I just completed benchmarking: the cached wakeup with the current naive
drivers makes no difference (at one stage I was playing with batched
hypercalls, where it seemed to help).
Thanks Christoph, DaveM!
===
Remove export of __put_task_struct, and usage in lguest
lguest takes a reference count of tasks for two reasons. The first is
bogus: the /dev/lguest close callback will be called before the task
is destroyed anyway, so no need to take a reference on open.
The second is code to defer waking up tasks for inter-guest I/O, but
the current lguest drivers are too simplistic to benefit (only batched
hypercalls will see an effect, and it's likely that lguests' entire
I/O model will be replaced with virtio and ringbuffers anyway).
Signed-off-by: Rusty Russell <[email protected]>
---
drivers/lguest/hypercalls.c | 1 -
drivers/lguest/io.c | 18 +-----------------
drivers/lguest/lg.h | 1 -
drivers/lguest/lguest_user.c | 2 --
kernel/fork.c | 1 -
5 files changed, 1 insertion(+), 22 deletions(-)
===================================================================
--- a/drivers/lguest/hypercalls.c
+++ b/drivers/lguest/hypercalls.c
@@ -189,5 +189,4 @@ void do_hypercalls(struct lguest *lg)
do_hcall(lg, lg->regs);
clear_hcall(lg);
}
- set_wakeup_process(lg, NULL);
}
===================================================================
--- a/drivers/lguest/io.c
+++ b/drivers/lguest/io.c
@@ -296,7 +296,7 @@ static int dma_transfer(struct lguest *s
/* Do this last so dst doesn't simply sleep on lock. */
set_bit(dst->interrupt, dstlg->irqs_pending);
- set_wakeup_process(srclg, dstlg->tsk);
+ wake_up_process(dstlg->tsk);
return i == dst->num_dmas;
fail:
@@ -333,7 +333,6 @@ again:
/* Give any recipients one chance to restock. */
up_read(¤t->mm->mmap_sem);
mutex_unlock(&lguest_lock);
- set_wakeup_process(lg, NULL);
empty++;
goto again;
}
@@ -360,21 +359,6 @@ void release_all_dma(struct lguest *lg)
unlink_dma(&lg->dma[i]);
}
up_read(&lg->mm->mmap_sem);
-}
-
-/* We cache one process to wakeup: helps for batching & wakes outside locks. */
-void set_wakeup_process(struct lguest *lg, struct task_struct *p)
-{
- if (p == lg->wake)
- return;
-
- if (lg->wake) {
- wake_up_process(lg->wake);
- put_task_struct(lg->wake);
- }
- lg->wake = p;
- if (lg->wake)
- get_task_struct(lg->wake);
}
/* Userspace wants a dma buffer from this guest. */
===================================================================
--- a/drivers/lguest/lg.h
+++ b/drivers/lguest/lg.h
@@ -240,7 +240,6 @@ void release_all_dma(struct lguest *lg);
void release_all_dma(struct lguest *lg);
unsigned long get_dma_buffer(struct lguest *lg, unsigned long key,
unsigned long *interrupt);
-void set_wakeup_process(struct lguest *lg, struct task_struct *p);
/* hypercalls.c: */
void do_hypercalls(struct lguest *lg);
===================================================================
--- a/drivers/lguest/lguest_user.c
+++ b/drivers/lguest/lguest_user.c
@@ -141,7 +141,6 @@ static int initialize(struct file *file,
setup_guest_gdt(lg);
init_clockdev(lg);
lg->tsk = current;
- get_task_struct(lg->tsk);
lg->mm = get_task_mm(lg->tsk);
init_waitqueue_head(&lg->break_wq);
lg->last_pages = NULL;
@@ -205,7 +204,6 @@ static int close(struct inode *inode, st
hrtimer_cancel(&lg->hrt);
release_all_dma(lg);
free_guest_pagetable(lg);
- put_task_struct(lg->tsk);
mmput(lg->mm);
if (!IS_ERR(lg->dead))
kfree(lg->dead);
===================================================================
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -128,7 +128,6 @@ void __put_task_struct(struct task_struc
if (!profile_handoff_task(tsk))
free_task(tsk);
}
-EXPORT_SYMBOL_GPL(__put_task_struct);
void __init fork_init(unsigned long mempages)
{
-
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