[GFS2] delay glock demote for a minimum hold time

When a lot of IO, with some distributed mmap IO, is run on a GFS2 filesystem in
a cluster, it will deadlock. The reason is that do_no_page() will repeatedly
call gfs2_sharewrite_nopage(), because each node keeps giving up the glock
too early, and is forced to call unmap_mapping_range(). This bumps the
mapping->truncate_count sequence count, forcing do_no_page() to retry. This
patch institutes a minimum glock hold time a tenth a second.  This insures
that even in heavy contention cases, the node has enough time to get some
useful work done before it gives up the glock.

A second issue is that when gfs2_glock_dq() is called from within a page fault
to demote a lock, and the associated page needs to be written out, it will
try to acqire a lock on it, but it has already been locked at a higher level.
This patch puts makes gfs2_glock_dq() use the work queue as well, to avoid this
issue. This is the same patch as Steve Whitehouse originally proposed to fix
this issue, execpt that gfs2_glock_dq() now grabs a reference to the glock
before it queues up the work on it.

Signed-off-by: Benjamin E. Marzinski <bmarzins@redhat.com>
Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>

3 files changed, 66 insertions, 16 deletions

diff --git a/fs/gfs2/glock.c b/fs/gfs2/glock.c
index 3d949187fed0..931368a385c8 100644
--- a/fs/gfs2/glock.c
+++ b/fs/gfs2/glock.c
@@ -27,6 +27,8 @@
 #include <linux/debugfs.h>
 #include <linux/kthread.h>
 #include <linux/freezer.h>
+#include <linux/workqueue.h>
+#include <linux/jiffies.h>
 
 #include "gfs2.h"
 #include "incore.h"
@@ -58,10 +60,13 @@ static int gfs2_dump_lockstate(struct gfs2_sbd *sdp);
 static int dump_glock(struct glock_iter *gi, struct gfs2_glock *gl);
 static void gfs2_glock_xmote_th(struct gfs2_glock *gl, struct gfs2_holder *gh);
 static void gfs2_glock_drop_th(struct gfs2_glock *gl);
+static void run_queue(struct gfs2_glock *gl);
+
 static DECLARE_RWSEM(gfs2_umount_flush_sem);
 static struct dentry *gfs2_root;
 static struct task_struct *scand_process;
 static unsigned int scand_secs = 5;
+static struct workqueue_struct *glock_workqueue;
 
 #define GFS2_GL_HASH_SHIFT      15
 #define GFS2_GL_HASH_SIZE       (1 << GFS2_GL_HASH_SHIFT)
@@ -277,6 +282,18 @@ static struct gfs2_glock *gfs2_glock_find(const struct gfs2_sbd *sdp,
         return gl;
 }
 
+static void glock_work_func(struct work_struct *work)
+{
+        struct gfs2_glock *gl = container_of(work, struct gfs2_glock, gl_work.work);
+
+        spin_lock(&gl->gl_spin);
+        if (test_and_clear_bit(GLF_PENDING_DEMOTE, &gl->gl_flags))
+                set_bit(GLF_DEMOTE, &gl->gl_flags);
+        run_queue(gl);
+        spin_unlock(&gl->gl_spin);
+        gfs2_glock_put(gl);
+}
+
 /**
  * gfs2_glock_get() - Get a glock, or create one if one doesn't exist
  * @sdp: The GFS2 superblock
@@ -316,6 +333,7 @@ int gfs2_glock_get(struct gfs2_sbd *sdp, u64 number,
         gl->gl_name = name;
         atomic_set(&gl->gl_ref, 1);
         gl->gl_state = LM_ST_UNLOCKED;
+        gl->gl_demote_state = LM_ST_EXCLUSIVE;
         gl->gl_hash = hash;
         gl->gl_owner_pid = 0;
         gl->gl_ip = 0;
@@ -324,10 +342,12 @@ int gfs2_glock_get(struct gfs2_sbd *sdp, u64 number,
         gl->gl_req_bh = NULL;
         gl->gl_vn = 0;
         gl->gl_stamp = jiffies;
+        gl->gl_tchange = jiffies;
         gl->gl_object = NULL;
         gl->gl_sbd = sdp;
         gl->gl_aspace = NULL;
         lops_init_le(&gl->gl_le, &gfs2_glock_lops);
+        INIT_DELAYED_WORK(&gl->gl_work, glock_work_func);
 
         /* If this glock protects actual on-disk data or metadata blocks,
            create a VFS inode to manage the pages/buffers holding them. */
@@ -441,6 +461,8 @@ static void wait_on_holder(struct gfs2_holder *gh)
 
 static void gfs2_demote_wake(struct gfs2_glock *gl)
 {
+        BUG_ON(!spin_is_locked(&gl->gl_spin));
+        gl->gl_demote_state = LM_ST_EXCLUSIVE;
         clear_bit(GLF_DEMOTE, &gl->gl_flags);
         smp_mb__after_clear_bit();
         wake_up_bit(&gl->gl_flags, GLF_DEMOTE);
@@ -682,10 +704,14 @@ static void gfs2_glmutex_unlock(struct gfs2_glock *gl)
  * practise: LM_ST_SHARED and LM_ST_UNLOCKED
  */
 
-static void handle_callback(struct gfs2_glock *gl, unsigned int state, int remote)
+static void handle_callback(struct gfs2_glock *gl, unsigned int state,
+                            int remote, unsigned long delay)
 {
+        int bit = delay ? GLF_PENDING_DEMOTE : GLF_DEMOTE;
+
         spin_lock(&gl->gl_spin);
-        if (test_and_set_bit(GLF_DEMOTE, &gl->gl_flags) == 0) {
+        set_bit(bit, &gl->gl_flags);
+        if (gl->gl_demote_state == LM_ST_EXCLUSIVE) {
                 gl->gl_demote_state = state;
                 gl->gl_demote_time = jiffies;
                 if (remote && gl->gl_ops->go_type == LM_TYPE_IOPEN &&
@@ -727,6 +753,7 @@ static void state_change(struct gfs2_glock *gl, unsigned int new_state)
         }
 
         gl->gl_state = new_state;
+        gl->gl_tchange = jiffies;
 }
 
 /**
@@ -813,7 +840,6 @@ out:
                 gl->gl_req_gh = NULL;
                 gl->gl_req_bh = NULL;
                 clear_bit(GLF_LOCK, &gl->gl_flags);
-                run_queue(gl);
                 spin_unlock(&gl->gl_spin);
         }
 
@@ -885,7 +911,6 @@ static void drop_bh(struct gfs2_glock *gl, unsigned int ret)
         gfs2_assert_warn(sdp, !ret);
 
         state_change(gl, LM_ST_UNLOCKED);
-        gfs2_demote_wake(gl);
 
         if (glops->go_inval)
                 glops->go_inval(gl, DIO_METADATA);
@@ -898,10 +923,10 @@ static void drop_bh(struct gfs2_glock *gl, unsigned int ret)
         }
 
         spin_lock(&gl->gl_spin);
+        gfs2_demote_wake(gl);
         gl->gl_req_gh = NULL;
         gl->gl_req_bh = NULL;
         clear_bit(GLF_LOCK, &gl->gl_flags);
-        run_queue(gl);
         spin_unlock(&gl->gl_spin);
 
         gfs2_glock_put(gl);
@@ -1209,9 +1234,10 @@ void gfs2_glock_dq(struct gfs2_holder *gh)
 {
         struct gfs2_glock *gl = gh->gh_gl;
         const struct gfs2_glock_operations *glops = gl->gl_ops;
+        unsigned delay = 0;
 
         if (gh->gh_flags & GL_NOCACHE)
-                handle_callback(gl, LM_ST_UNLOCKED, 0);
+                handle_callback(gl, LM_ST_UNLOCKED, 0, 0);
 
         gfs2_glmutex_lock(gl);
 
@@ -1229,8 +1255,14 @@ void gfs2_glock_dq(struct gfs2_holder *gh)
         }
 
         clear_bit(GLF_LOCK, &gl->gl_flags);
-        run_queue(gl);
         spin_unlock(&gl->gl_spin);
+
+        gfs2_glock_hold(gl);
+        if (test_bit(GLF_PENDING_DEMOTE, &gl->gl_flags) &&
+            !test_bit(GLF_DEMOTE, &gl->gl_flags))
+                delay = gl->gl_ops->go_min_hold_time;
+        if (queue_delayed_work(glock_workqueue, &gl->gl_work, delay) == 0)
+                gfs2_glock_put(gl);
 }
 
 void gfs2_glock_dq_wait(struct gfs2_holder *gh)
@@ -1457,18 +1489,21 @@ static void blocking_cb(struct gfs2_sbd *sdp, struct lm_lockname *name,
                         unsigned int state)
 {
         struct gfs2_glock *gl;
+        unsigned long delay = 0;
+        unsigned long holdtime;
+        unsigned long now = jiffies;
 
         gl = gfs2_glock_find(sdp, name);
         if (!gl)
                 return;
 
-        handle_callback(gl, state, 1);
-
-        spin_lock(&gl->gl_spin);
-        run_queue(gl);
-        spin_unlock(&gl->gl_spin);
+        holdtime = gl->gl_tchange + gl->gl_ops->go_min_hold_time;
+        if (time_before(now, holdtime))
+                delay = holdtime - now;
 
-        gfs2_glock_put(gl);
+        handle_callback(gl, state, 1, delay);
+        if (queue_delayed_work(glock_workqueue, &gl->gl_work, delay) == 0)
+                gfs2_glock_put(gl);
 }
 
 /**
@@ -1509,7 +1544,8 @@ void gfs2_glock_cb(void *cb_data, unsigned int type, void *data)
                         return;
                 if (!gfs2_assert_warn(sdp, gl->gl_req_bh))
                         gl->gl_req_bh(gl, async->lc_ret);
-                gfs2_glock_put(gl);
+                if (queue_delayed_work(glock_workqueue, &gl->gl_work, 0) == 0)
+                        gfs2_glock_put(gl);
                 up_read(&gfs2_umount_flush_sem);
                 return;
         }
@@ -1602,7 +1638,7 @@ void gfs2_reclaim_glock(struct gfs2_sbd *sdp)
         if (gfs2_glmutex_trylock(gl)) {
                 if (list_empty(&gl->gl_holders) &&
                     gl->gl_state != LM_ST_UNLOCKED && demote_ok(gl))
-                        handle_callback(gl, LM_ST_UNLOCKED, 0);
+                        handle_callback(gl, LM_ST_UNLOCKED, 0, 0);
                 gfs2_glmutex_unlock(gl);
         }
 
@@ -1702,7 +1738,7 @@ static void clear_glock(struct gfs2_glock *gl)
         if (gfs2_glmutex_trylock(gl)) {
                 if (list_empty(&gl->gl_holders) &&
                     gl->gl_state != LM_ST_UNLOCKED)
-                        handle_callback(gl, LM_ST_UNLOCKED, 0);
+                        handle_callback(gl, LM_ST_UNLOCKED, 0, 0);
                 gfs2_glmutex_unlock(gl);
         }
 }
@@ -2009,11 +2045,18 @@ int __init gfs2_glock_init(void)
         if (IS_ERR(scand_process))
                 return PTR_ERR(scand_process);
 
+        glock_workqueue = create_workqueue("glock_workqueue");
+        if (IS_ERR(glock_workqueue)) {
+                kthread_stop(scand_process);
+                return PTR_ERR(glock_workqueue);
+        }
+
         return 0;
 }
 
 void gfs2_glock_exit(void)
 {
+        destroy_workqueue(glock_workqueue);
         kthread_stop(scand_process);
 }
 
diff --git a/fs/gfs2/glops.c b/fs/gfs2/glops.c
index 88342e0b4bc7..7ef6b23bb38a 100644
--- a/fs/gfs2/glops.c
+++ b/fs/gfs2/glops.c
@@ -454,6 +454,7 @@ const struct gfs2_glock_operations gfs2_inode_glops = {
         .go_lock = inode_go_lock,
         .go_unlock = inode_go_unlock,
         .go_type = LM_TYPE_INODE,
+        .go_min_hold_time = HZ / 10,
 };
 
 const struct gfs2_glock_operations gfs2_rgrp_glops = {
@@ -464,6 +465,7 @@ const struct gfs2_glock_operations gfs2_rgrp_glops = {
         .go_lock = rgrp_go_lock,
         .go_unlock = rgrp_go_unlock,
         .go_type = LM_TYPE_RGRP,
+        .go_min_hold_time = HZ / 10,
 };
 
 const struct gfs2_glock_operations gfs2_trans_glops = {
diff --git a/fs/gfs2/incore.h b/fs/gfs2/incore.h
index 1390b30daf19..23b611aa70d2 100644
--- a/fs/gfs2/incore.h
+++ b/fs/gfs2/incore.h
@@ -11,6 +11,7 @@
 #define __INCORE_DOT_H__
 
 #include <linux/fs.h>
+#include <linux/workqueue.h>
 
 #define DIO_WAIT        0x00000010
 #define DIO_METADATA    0x00000020
@@ -130,6 +131,7 @@ struct gfs2_glock_operations {
         int (*go_lock) (struct gfs2_holder *gh);
         void (*go_unlock) (struct gfs2_holder *gh);
         const int go_type;
+        const unsigned long go_min_hold_time;
 };
 
 enum {
@@ -161,6 +163,7 @@ enum {
         GLF_LOCK                = 1,
         GLF_STICKY              = 2,
         GLF_DEMOTE              = 3,
+        GLF_PENDING_DEMOTE      = 4,
         GLF_DIRTY               = 5,
 };
 
@@ -193,6 +196,7 @@ struct gfs2_glock {
 
         u64 gl_vn;
         unsigned long gl_stamp;
+        unsigned long gl_tchange;
         void *gl_object;
 
         struct list_head gl_reclaim;
@@ -203,6 +207,7 @@ struct gfs2_glock {
         struct gfs2_log_element gl_le;
         struct list_head gl_ail_list;
         atomic_t gl_ail_count;
+        struct delayed_work gl_work;
 };
 
 struct gfs2_alloc {