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SubjectRe: please revert kthread from loop.c
Quoting Andrew Morton (akpm@osdl.org):
> I'm not sure why it's all so tricky in there, really. Loop is doing a
> pretty conventional stop, wakeup, stick-things-on-lists operation and we do
> that all over the kernel using pretty well-understood idioms. But for some
> reason, loop is all difficult about it. I wonder why. hm.

Does this version, going back to using a completion - lo->lo_wait - seem
a touch simpler?

thanks,
-serge

From: "Serge E. Hallyn" <serue@us.ibm.com>
Subject: [PATCH] kthread: convert loop.c to kthread

Convert loop.c from the deprecated kernel_thread to kthread.

This version goes back to using a completion for waking the
loop_thread when there is work to do. Ending the loop thread
is done by first setting the state, then waking the thread
using the completion, and finally calling kthread_stop().
The loop_thread is either already awake serving requests,
or is awoken by loop_clr_fd()s complete. It does one more
loop to serve pending requests, after which it sees it's
state is no longer running, and starts a short busyloop
while waiting to be reaped.

Signed-off-by: Serge Hallyn <serue@us.ibm.com>

---
drivers/block/loop.c | 73 +++++++++++++++++++-------------------------------
include/linux/loop.h | 4 +--
2 files changed, 30 insertions(+), 47 deletions(-)
5aa946838754cc8bd1582ca3f926cf51d7e21df8
diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index ccaada1..8779194 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -72,6 +72,7 @@
#include <linux/completion.h>
#include <linux/highmem.h>
#include <linux/gfp.h>
+#include <linux/kthread.h>

#include <asm/uaccess.h>

@@ -524,13 +525,11 @@ static int loop_make_request(request_que
goto out;
lo->lo_pending++;
loop_add_bio(lo, old_bio);
+ complete(&lo->lo_wait);
spin_unlock_irq(&lo->lo_lock);
- complete(&lo->lo_bh_done);
return 0;

out:
- if (lo->lo_pending == 0)
- complete(&lo->lo_bh_done);
spin_unlock_irq(&lo->lo_lock);
bio_io_error(old_bio, old_bio->bi_size);
return 0;
@@ -576,8 +575,6 @@ static int loop_thread(void *data)
struct loop_device *lo = data;
struct bio *bio;

- daemonize("loop%d", lo->lo_number);
-
/*
* loop can be used in an encrypted device,
* hence, it mustn't be stopped at all
@@ -587,47 +584,28 @@ static int loop_thread(void *data)

set_user_nice(current, -20);

- lo->lo_state = Lo_bound;
- lo->lo_pending = 1;
-
- /*
- * complete it, we are running
- */
- complete(&lo->lo_done);
-
for (;;) {
- int pending;
-
- if (wait_for_completion_interruptible(&lo->lo_bh_done))
- continue;
-
spin_lock_irq(&lo->lo_lock);
+ while (lo->lo_pending) {
+ bio = loop_get_bio(lo);
+ lo->lo_pending--;

- /*
- * could be completed because of tear-down, not pending work
- */
- if (unlikely(!lo->lo_pending)) {
spin_unlock_irq(&lo->lo_lock);
- break;
+ BUG_ON(!bio);
+ loop_handle_bio(lo, bio);
+ spin_lock_irq(&lo->lo_lock);
}

- bio = loop_get_bio(lo);
- lo->lo_pending--;
- pending = lo->lo_pending;
+ if (lo->lo_state == Lo_rundown) {
+ spin_unlock_irq(&lo->lo_lock);
+ while (!kthread_should_stop());
+ break;
+ }
spin_unlock_irq(&lo->lo_lock);

- BUG_ON(!bio);
- loop_handle_bio(lo, bio);
-
- /*
- * upped both for pending work and tear-down, lo_pending
- * will hit zero then
- */
- if (unlikely(!pending))
- break;
+ wait_for_completion_interruptible(&lo->lo_wait);
}

- complete(&lo->lo_done);
return 0;
}

@@ -846,10 +824,16 @@ static int loop_set_fd(struct loop_devic

set_blocksize(bdev, lo_blocksize);

- error = kernel_thread(loop_thread, lo, CLONE_KERNEL);
- if (error < 0)
+ lo->lo_thread = kthread_create(loop_thread, lo, "loop%d",
+ lo->lo_number);
+ if (IS_ERR(lo->lo_thread)) {
+ error = PTR_ERR(lo->lo_thread);
+ lo->lo_thread = NULL;
goto out_putf;
- wait_for_completion(&lo->lo_done);
+ }
+ lo->lo_pending = 0;
+ lo->lo_state = Lo_bound;
+ wake_up_process(lo->lo_thread);
return 0;

out_putf:
@@ -913,12 +897,10 @@ static int loop_clr_fd(struct loop_devic

spin_lock_irq(&lo->lo_lock);
lo->lo_state = Lo_rundown;
- lo->lo_pending--;
- if (!lo->lo_pending)
- complete(&lo->lo_bh_done);
+ complete(&lo->lo_wait);
spin_unlock_irq(&lo->lo_lock);

- wait_for_completion(&lo->lo_done);
+ kthread_stop(lo->lo_thread);

lo->lo_backing_file = NULL;

@@ -928,6 +910,7 @@ static int loop_clr_fd(struct loop_devic
lo->lo_device = NULL;
lo->lo_encryption = NULL;
lo->lo_offset = 0;
+ lo->lo_thread = NULL;
lo->lo_sizelimit = 0;
lo->lo_encrypt_key_size = 0;
lo->lo_flags = 0;
@@ -1293,8 +1276,8 @@ static int __init loop_init(void)
if (!lo->lo_queue)
goto out_mem4;
mutex_init(&lo->lo_ctl_mutex);
- init_completion(&lo->lo_done);
- init_completion(&lo->lo_bh_done);
+ init_completion(&lo->lo_wait);
+ lo->lo_thread = NULL;
lo->lo_number = i;
spin_lock_init(&lo->lo_lock);
disk->major = LOOP_MAJOR;
diff --git a/include/linux/loop.h b/include/linux/loop.h
index e76c761..c9a0a45 100644
--- a/include/linux/loop.h
+++ b/include/linux/loop.h
@@ -59,8 +59,8 @@ struct loop_device {
struct bio *lo_bio;
struct bio *lo_biotail;
int lo_state;
- struct completion lo_done;
- struct completion lo_bh_done;
+ struct completion lo_wait;
+ struct task_struct *lo_thread;
struct mutex lo_ctl_mutex;
int lo_pending;

--
1.1.6
-
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