[GFS2] flocks from same process trip kernel BUG at fs/gfs2/glock.c:1118!

This patch adds a new flag to the gfs2_holder structure GL_FLOCK.
It is set on holders of glocks representing flocks. This flag is
checked in add_to_queue() and a process is permitted to queue more
than one holder onto a glock if it is set. This solves the issue
of a process not being able to do multiple flocks on the same file.
Through a single descriptor, a process can now promote and demote
flocks. Through multiple descriptors a process can now queue
multiple flocks on the same file. There's still the problem of
a process deadlocking itself (because gfs2 blocking locks are not
interruptible) by queueing incompatible deadlock.

Signed-off-by: Abhijith Das <adas@redhat.com>
Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>

1 files changed, 25 insertions, 18 deletions

diff --git a/fs/gfs2/glock.c b/fs/gfs2/glock.c
index 931368a385c8..d631cad0aeee 100644
--- a/fs/gfs2/glock.c
+++ b/fs/gfs2/glock.c
@@ -1106,24 +1106,31 @@ static void add_to_queue(struct gfs2_holder *gh)
         if (test_and_set_bit(HIF_WAIT, &gh->gh_iflags))
                 BUG();
 
-        existing = find_holder_by_owner(&gl->gl_holders, gh->gh_owner_pid);
-        if (existing) {
-                print_symbol(KERN_WARNING "original: %s\n", existing->gh_ip);
-                printk(KERN_INFO "pid : %d\n", existing->gh_owner_pid);
-                printk(KERN_INFO "lock type : %d lock state : %d\n",
-                                existing->gh_gl->gl_name.ln_type, existing->gh_gl->gl_state);
-                print_symbol(KERN_WARNING "new: %s\n", gh->gh_ip);
-                printk(KERN_INFO "pid : %d\n", gh->gh_owner_pid);
-                printk(KERN_INFO "lock type : %d lock state : %d\n",
-                                gl->gl_name.ln_type, gl->gl_state);
-                BUG();
-        }
-
-        existing = find_holder_by_owner(&gl->gl_waiters3, gh->gh_owner_pid);
-        if (existing) {
-                print_symbol(KERN_WARNING "original: %s\n", existing->gh_ip);
-                print_symbol(KERN_WARNING "new: %s\n", gh->gh_ip);
-                BUG();
+        if (!(gh->gh_flags & GL_FLOCK)) {
+                existing = find_holder_by_owner(&gl->gl_holders, 
+                                                gh->gh_owner_pid);
+                if (existing) {
+                        print_symbol(KERN_WARNING "original: %s\n", 
+                                     existing->gh_ip);
+                        printk(KERN_INFO "pid : %d\n", existing->gh_owner_pid);
+                        printk(KERN_INFO "lock type : %d lock state : %d\n",
+                               existing->gh_gl->gl_name.ln_type, 
+                               existing->gh_gl->gl_state);
+                        print_symbol(KERN_WARNING "new: %s\n", gh->gh_ip);
+                        printk(KERN_INFO "pid : %d\n", gh->gh_owner_pid);
+                        printk(KERN_INFO "lock type : %d lock state : %d\n",
+                               gl->gl_name.ln_type, gl->gl_state);
+                        BUG();
+                }
+                
+                existing = find_holder_by_owner(&gl->gl_waiters3, 
+                                                gh->gh_owner_pid);
+                if (existing) {
+                        print_symbol(KERN_WARNING "original: %s\n", 
+                                     existing->gh_ip);
+                        print_symbol(KERN_WARNING "new: %s\n", gh->gh_ip);
+                        BUG();
+                }
         }
 
         if (gh->gh_flags & LM_FLAG_PRIORITY)