[Cluster-devel] [GFS2 PATCH] GFS2: Only wait for demote when last holder is dequeued

2014-06-20 Thread Bob Peterson
Hi,

Function gfs2_glock_dq_wait is supposed to dequeue a glock and then
wait for the lock to be demoted. The problem is, if this is a shared
lock, its demote will depend on the other holders, which means you
might end up waiting forever because the other process is blocked.
This problem is especially apparent when dealing with nested flocks.

Regards,

Bob Peterson
Red Hat File Systems

Signed-off-by: Bob Peterson rpete...@redhat.com 
---
diff --git a/fs/gfs2/glock.c b/fs/gfs2/glock.c
index aec7f73..22ce2f0 100644
--- a/fs/gfs2/glock.c
+++ b/fs/gfs2/glock.c
@@ -1128,7 +1128,9 @@ void gfs2_glock_dq_wait(struct gfs2_holder *gh)
struct gfs2_glock *gl = gh-gh_gl;
gfs2_glock_dq(gh);
might_sleep();
-   wait_on_bit(gl-gl_flags, GLF_DEMOTE, gfs2_glock_demote_wait, 
TASK_UNINTERRUPTIBLE);
+   if (!find_first_holder(gl))
+   wait_on_bit(gl-gl_flags, GLF_DEMOTE, gfs2_glock_demote_wait,
+   TASK_UNINTERRUPTIBLE);
 }
 
 /**



Re: [Cluster-devel] [GFS2 PATCH] GFS2: Only wait for demote when last holder is dequeued

2014-06-20 Thread Steven Whitehouse

Hi,

Now in the -nmw tree. Thanks,

Steve.

On 20/06/14 14:36, Bob Peterson wrote:

Hi,

Function gfs2_glock_dq_wait is supposed to dequeue a glock and then
wait for the lock to be demoted. The problem is, if this is a shared
lock, its demote will depend on the other holders, which means you
might end up waiting forever because the other process is blocked.
This problem is especially apparent when dealing with nested flocks.

Regards,

Bob Peterson
Red Hat File Systems

Signed-off-by: Bob Peterson rpete...@redhat.com
---
diff --git a/fs/gfs2/glock.c b/fs/gfs2/glock.c
index aec7f73..22ce2f0 100644
--- a/fs/gfs2/glock.c
+++ b/fs/gfs2/glock.c
@@ -1128,7 +1128,9 @@ void gfs2_glock_dq_wait(struct gfs2_holder *gh)
struct gfs2_glock *gl = gh-gh_gl;
gfs2_glock_dq(gh);
might_sleep();
-   wait_on_bit(gl-gl_flags, GLF_DEMOTE, gfs2_glock_demote_wait, 
TASK_UNINTERRUPTIBLE);
+   if (!find_first_holder(gl))
+   wait_on_bit(gl-gl_flags, GLF_DEMOTE, gfs2_glock_demote_wait,
+   TASK_UNINTERRUPTIBLE);
  }
  
  /**