[Cluster-devel] [GFS2 PATCH 1/2] GFS2: Make gfs2_clear_inode() queue the final put

[Steven Whitehouse]

Hi,

On 19/11/15 18:42, Bob Peterson wrote:
> This patch changes function gfs2_clear_inode() so that instead
> of calling gfs2_glock_put directly() most of the time, it queues
> the glock to the delayed work queue. That avoids a possible
> deadlock where it calls dlm during a fence operation:
> dlm waits for a fence operation, the fence operation waits for
> memory, the shrinker waits for gfs2 to free an inode from memory,
> but gfs2 waits for dlm.
>
> Signed-off-by: Bob Peterson <rpeterso at redhat.com>
> ---
>   fs/gfs2/glock.c | 34 +++++++++++++++++-----------------
>   fs/gfs2/glock.h |  1 +
>   fs/gfs2/super.c |  5 ++++-
>   3 files changed, 22 insertions(+), 18 deletions(-)
[snip]
Most of the patch seems to just rename the workqueue which makes it 
tricky to spot the other changes. However, the below code seems to be 
the new bit..

> diff --git a/fs/gfs2/super.c b/fs/gfs2/super.c
> index 9d5c3f7..46e5004 100644
> --- a/fs/gfs2/super.c
> +++ b/fs/gfs2/super.c
> @@ -24,6 +24,7 @@
>   #include <linux/crc32.h>
>   #include <linux/time.h>
>   #include <linux/wait.h>
> +#include <linux/workqueue.h>
>   #include <linux/writeback.h>
>   #include <linux/backing-dev.h>
>   #include <linux/kernel.h>
> @@ -1614,7 +1615,9 @@ out:
>   	ip->i_gl->gl_object = NULL;
>   	flush_delayed_work(&ip->i_gl->gl_work);
>   	gfs2_glock_add_to_lru(ip->i_gl);
> -	gfs2_glock_put(ip->i_gl);
> +	if (queue_delayed_work(gfs2_glock_workqueue,
> +			       &ip->i_gl->gl_work, 0) == 0)
> +		gfs2_glock_put(ip->i_gl);
>   	ip->i_gl = NULL;
>   	if (ip->i_iopen_gh.gh_gl) {
>   		ip->i_iopen_gh.gh_gl->gl_object = NULL;

which replaces a put with a queue & put if the queue fails (due to it 
being already on the queue) which doesn't look quite right to be since 
if calling gfs2_glock_put() was not safe before, then calling it 
conditionally like this is still no safer I think?

Steve.