[PATCH] relay: move remove_buf_file inside relay_close_buf

[Dmitry Monakhov]

Currently remove_buf_file callback is called from from kobject
release method. This result in follow issue:
# blktrace -d /dev/sda1 -d /dev/sda -o test
blktrace_setup()
dir = create_dir()
rchan = relay_open(dir,...)
->create_buf_file_callback
buf_file = debugfs_create_file(dir, )

Userspace will open buf_file.
Later we make a decision to stop tracing
blktrace_down()
relay_close(rhcan) /* just decrement kobj reference */
/* since it is not zero then callback not called */
debugfs_remove(dir) /* FAIL due to non empty dir */

Later user space will close the file and file will be deleted,
but directory still exist.
user_space_close()
->file_release
->release_buf_file_callback
->debugfs_remove(buf_file)

In fact this is general issue, blktrace is just one of examples.
We can not reliably remove parent dir until all users close the
buf_file.

We don't have to wait this long. File may be deleted
inside relay_close_buf().

Signed-off-by: Dmitry Monakhov <dmon...@openvz.org>
---
kernel/relay.c | 2 +-
1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/kernel/relay.c b/kernel/relay.c
index c705a41..dcf71c8 100644
--- a/kernel/relay.c
+++ b/kernel/relay.c
@@ -237,7 +237,6 @@ static void relay_destroy_buf(struct rchan_buf *buf)
static void relay_remove_buf(struct kref *kref)
{
struct rchan_buf *buf = container_of(kref, struct rchan_buf, kref);
- buf->chan->cb->remove_buf_file(buf->dentry);
relay_destroy_buf(buf);
}

@@ -487,6 +486,7 @@ static void relay_close_buf(struct rchan_buf *buf)
{
buf->finalized = 1;
del_timer_sync(&buf->timer);
+ buf->chan->cb->remove_buf_file(buf->dentry);
kref_put(&buf->kref, relay_remove_buf);
}

--
1.6.6

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[Jens Axboe]

Thanks, I believe this fixes a long standing problem we've had with
blktrace. You can add my acked-by.

--
Jens Axboe

[Dmitry Monakhov]

add Tom Zanussi to recipients.
Tom, please take a look at the patch, it is simple and clean and it able
to solve long standing blktrace related bug.

[Tom Zanussi]

On Tue, 2010-04-06 at 13:34 +0400, Dmitry Monakhov wrote:
> add Tom Zanussi to recipients.
> Tom, please take a look at the patch, it is simple and clean and it able
> to solve long standing blktrace related bug.

Hi,

It looks ok to me - I don't see any problems with it, but you should
probably get the official relay maintainer(s?) to take a look at it as
well - adding them to the cc: list.

Tom