Re: please revert kthread from loop.c

From: Serge E. Hallyn
Date: Thu Jul 20 2006 - 13:05:57 EST

Quoting Andrew Morton (akpm@xxxxxxxx):
> On Thu, 13 Jul 2006 08:36:02 -0500
> "Serge E. Hallyn" <serue@xxxxxxxxxx> wrote:
>
> > Quoting Andrew Morton (akpm@xxxxxxxx):
> >
> > > Again: why is this so hard? It shouldn't be. Perhaps because loop is
> > > using completions in bizarre ways where it should be using
> > > wake_up_process(), wait_event(), etc.
> >
> > Ah.
> >
> > wait_event() actually seems like the way to go - I'll try to follow the
> > example in fs/ocfs2/journal.c.
>
> I suspect quite a lot of changes to loop.c would fall out. For a start, in
> a sufficiently-simplified implementation lo_pending would perhaps go away -
> just test the NULLness of the top of the list of BIOs.

True - here is an attempt at that:

Subject: [PATCH] kthread: convert loop.c to kthread
From: Serge E. Hallyn <hallyn@sergelap.(none)>
Date: 1153345222 -0500

Convert loop.c from the deprecated kernel_thread to kthread.
This patch simplifies the code quite a bit and passes similar
testing to the previous submission on both emulated x86 and
s390.

Changes since last submission:
switched to using a rather simple loop based on
wait_event_interruptible.

Signed-off-by: Serge E. Hallyn <serue@xxxxxxxxxx>

---

drivers/block/loop.c | 69 +++++++++++++++++---------------------------------
include/linux/loop.h | 5 +---
2 files changed, 26 insertions(+), 48 deletions(-)

c5f5e9d7016d6fb2b43aa4b13aea302ac367a28c
diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index 7b3b94d..0468785 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>

@@ -522,15 +523,12 @@ static int loop_make_request(request_que
goto out;
if (unlikely(rw == WRITE && (lo->lo_flags & LO_FLAGS_READ_ONLY)))
goto out;
- lo->lo_pending++;
loop_add_bio(lo, old_bio);
+ wake_up(&lo->lo_event);
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;
@@ -570,14 +568,18 @@ static inline void loop_handle_bio(struc
* to avoid blocking in our make_request_fn. it also does loop decrypting
* on reads for block backed loop, as that is too heavy to do from
* b_end_io context where irqs may be disabled.
+ *
+ * Loop explanation: loop_clr_fd() sets lo_state to Lo_rundown before
+ * calling kthread_stop(). Therefore once kthread_should_stop() is
+ * true, make_request will not place any more requests. Therefore
+ * once kthread_should_stop() is true and lo_bio is NULL, we are
+ * done with the loop.
*/
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 +589,21 @@ 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);
+ while (!kthread_should_stop() || lo->lo_bio) {

- for (;;) {
- int pending;
+ wait_event_interruptible(lo->lo_event,
+ lo->lo_bio || kthread_should_stop());

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

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

@@ -837,10 +813,15 @@ 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_state = Lo_bound;
+ wake_up_process(lo->lo_thread);
return 0;

out_putf:
@@ -904,12 +885,9 @@ 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);
spin_unlock_irq(&lo->lo_lock);

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

lo->lo_backing_file = NULL;

@@ -922,6 +900,7 @@ static int loop_clr_fd(struct loop_devic
lo->lo_sizelimit = 0;
lo->lo_encrypt_key_size = 0;
lo->lo_flags = 0;
+ lo->lo_thread = NULL;
memset(lo->lo_encrypt_key, 0, LO_KEY_SIZE);
memset(lo->lo_crypt_name, 0, LO_NAME_SIZE);
memset(lo->lo_file_name, 0, LO_NAME_SIZE);
@@ -1284,9 +1263,9 @@ 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);
lo->lo_number = i;
+ lo->lo_thread = NULL;
+ init_waitqueue_head(&lo->lo_event);
spin_lock_init(&lo->lo_lock);
disk->major = LOOP_MAJOR;
disk->first_minor = i;
diff --git a/include/linux/loop.h b/include/linux/loop.h
index e76c761..191a595 100644
--- a/include/linux/loop.h
+++ b/include/linux/loop.h
@@ -59,10 +59,9 @@ struct loop_device {
struct bio *lo_bio;
struct bio *lo_biotail;
int lo_state;
- struct completion lo_done;
- struct completion lo_bh_done;
struct mutex lo_ctl_mutex;
- int lo_pending;
+ struct task_struct *lo_thread;
+ wait_queue_head_t lo_event;

request_queue_t *lo_queue;
};
--
1.1.6
-
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