Date:	Wed, 13 Apr 2011 10:20:54 +0100
From:	Steven Whitehouse <swhiteho@...hat.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	James Bottomley <James.Bottomley@...senPartnership.com>,
	linux-kernel@...r.kernel.org, Jens Axboe <jaxboe@...ionio.com>
Subject: Re: Strange block/scsi/workqueue issue

Hi,

On Wed, 2011-04-13 at 15:06 +0900, Tejun Heo wrote:
> On Wed, Apr 13, 2011 at 02:18:46PM +0900, Tejun Heo wrote:
> > Steven, can you be enticed to try the combination?  I'll prep a
> > combined patch and post it but please beware that I'm currently in a
> > rather zombish state - sleep deprived, jet lagged and malfunctioning
> > digestion - so the likelihood of doing something stupid is pretty
> > high.
> 
> Does the following completely untested version work?
> 
Almost. With one small change (q->queue_lock is already a pointer to a
spinlock, so it doesn't require an &) it seems to work for me. Let me
know if you'd like me to do any more tests. I've attached an updated
patch below,

Steve.


diff --git a/block/blk-core.c b/block/blk-core.c
index 90f22cc..90de9ac 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -359,6 +359,14 @@ void blk_put_queue(struct request_queue *q)
  */
 void blk_cleanup_queue(struct request_queue *q)
 {
+	/* mark @q stopped and dead */
+	mutex_lock(&q->sysfs_lock);
+	spin_lock_irq(q->queue_lock);
+	queue_flag_set(QUEUE_FLAG_STOPPED, q);
+	queue_flag_set(QUEUE_FLAG_DEAD, q);
+	spin_unlock_irq(q->queue_lock);
+	mutex_unlock(&q->sysfs_lock);
+
 	/*
 	 * We know we have process context here, so we can be a little
 	 * cautious and ensure that pending block actions on this device
@@ -368,9 +376,6 @@ void blk_cleanup_queue(struct request_queue *q)
 	blk_sync_queue(q);
 
 	del_timer_sync(&q->backing_dev_info.laptop_mode_wb_timer);
-	mutex_lock(&q->sysfs_lock);
-	queue_flag_set_unlocked(QUEUE_FLAG_DEAD, q);
-	mutex_unlock(&q->sysfs_lock);
 
 	if (q->elevator)
 		elevator_exit(q->elevator);
@@ -1456,7 +1461,7 @@ static inline int bio_check_eod(struct bio *bio, unsigned int nr_sectors)
  * generic_make_request and the drivers it calls may use bi_next if this
  * bio happens to be merged with someone else, and may change bi_dev and
  * bi_sector for remaps as it sees fit.  So the values of these fields
- * should NOT be depended on after the call to generic_make_request.
+ * should NOT be depended on after thes call to generic_make_request.
  */
 static inline void __generic_make_request(struct bio *bio)
 {
diff --git a/block/blk.h b/block/blk.h
index 6126346..4df474d 100644
--- a/block/blk.h
+++ b/block/blk.h
@@ -62,7 +62,8 @@ static inline struct request *__elv_next_request(struct request_queue *q)
 			return rq;
 		}
 
-		if (!q->elevator->ops->elevator_dispatch_fn(q, 0))
+		if (test_bit(QUEUE_FLAG_DEAD, &q->queue_flags) ||
+		    !q->elevator->ops->elevator_dispatch_fn(q, 0))
 			return NULL;
 	}
 }
diff --git a/drivers/scsi/scsi.c b/drivers/scsi/scsi.c
index 2aeb2e9..12ebcbc 100644
--- a/drivers/scsi/scsi.c
+++ b/drivers/scsi/scsi.c
@@ -70,6 +70,11 @@
 #define CREATE_TRACE_POINTS
 #include <trace/events/scsi.h>
 
+/*
+ * Utility multithreaded workqueue for SCSI.
+ */
+struct workqueue_struct *scsi_wq;
+
 static void scsi_done(struct scsi_cmnd *cmd);
 
 /*
@@ -1306,11 +1311,14 @@ MODULE_PARM_DESC(scsi_logging_level, "a bit mask of logging levels");
 
 static int __init init_scsi(void)
 {
-	int error;
+	int error = -ENOMEM;
 
+	scsi_wq = alloc_workqueue("scsi", 0, 0);
+	if (!scsi_wq)
+		return error;
 	error = scsi_init_queue();
 	if (error)
-		return error;
+		goto cleanup_wq;
 	error = scsi_init_procfs();
 	if (error)
 		goto cleanup_queue;
@@ -1342,6 +1350,8 @@ cleanup_procfs:
 	scsi_exit_procfs();
 cleanup_queue:
 	scsi_exit_queue();
+cleanup_wq:
+	destroy_workqueue(scsi_wq);
 	printk(KERN_ERR "SCSI subsystem failed to initialize, error = %d\n",
 	       -error);
 	return error;
@@ -1356,6 +1366,7 @@ static void __exit exit_scsi(void)
 	scsi_exit_devinfo();
 	scsi_exit_procfs();
 	scsi_exit_queue();
+	destroy_workqueue(scsi_wq);
 }
 
 subsys_initcall(init_scsi);
diff --git a/drivers/scsi/scsi_scan.c b/drivers/scsi/scsi_scan.c
index 087821f..4222b58 100644
--- a/drivers/scsi/scsi_scan.c
+++ b/drivers/scsi/scsi_scan.c
@@ -362,6 +362,16 @@ int scsi_is_target_device(const struct device *dev)
 }
 EXPORT_SYMBOL(scsi_is_target_device);
 
+static void scsi_target_reap_usercontext(struct work_struct *work)
+{
+	struct scsi_target *starget =
+		container_of(work, struct scsi_target, reap_work);
+
+	transport_remove_device(&starget->dev);
+	device_del(&starget->dev);
+	scsi_target_destroy(starget);
+}
+
 static struct scsi_target *__scsi_find_target(struct device *parent,
 					      int channel, uint id)
 {
@@ -427,6 +437,7 @@ static struct scsi_target *scsi_alloc_target(struct device *parent,
 	starget->state = STARGET_CREATED;
 	starget->scsi_level = SCSI_2;
 	starget->max_target_blocked = SCSI_DEFAULT_TARGET_BLOCKED;
+	INIT_WORK(&starget->reap_work, scsi_target_reap_usercontext);
  retry:
 	spin_lock_irqsave(shost->host_lock, flags);
 
@@ -462,21 +473,11 @@ static struct scsi_target *scsi_alloc_target(struct device *parent,
 	}
 	/* Unfortunately, we found a dying target; need to
 	 * wait until it's dead before we can get a new one */
+	flush_work(&found_target->reap_work);
 	put_device(&found_target->dev);
-	flush_scheduled_work();
 	goto retry;
 }
 
-static void scsi_target_reap_usercontext(struct work_struct *work)
-{
-	struct scsi_target *starget =
-		container_of(work, struct scsi_target, ew.work);
-
-	transport_remove_device(&starget->dev);
-	device_del(&starget->dev);
-	scsi_target_destroy(starget);
-}
-
 /**
  * scsi_target_reap - check to see if target is in use and destroy if not
  * @starget: target to be checked
@@ -507,8 +508,7 @@ void scsi_target_reap(struct scsi_target *starget)
 	if (state == STARGET_CREATED)
 		scsi_target_destroy(starget);
 	else
-		execute_in_process_context(scsi_target_reap_usercontext,
-					   &starget->ew);
+		queue_work(scsi_wq, &starget->reap_work);
 }
 
 /**
diff --git a/drivers/scsi/scsi_sysfs.c b/drivers/scsi/scsi_sysfs.c
index e44ff64..e030091 100644
--- a/drivers/scsi/scsi_sysfs.c
+++ b/drivers/scsi/scsi_sysfs.c
@@ -300,7 +300,7 @@ static void scsi_device_dev_release_usercontext(struct work_struct *work)
 	struct list_head *this, *tmp;
 	unsigned long flags;
 
-	sdev = container_of(work, struct scsi_device, ew.work);
+	sdev = container_of(work, struct scsi_device, release_work);
 
 	parent = sdev->sdev_gendev.parent;
 	starget = to_scsi_target(parent);
@@ -323,7 +323,6 @@ static void scsi_device_dev_release_usercontext(struct work_struct *work)
 	}
 
 	if (sdev->request_queue) {
-		sdev->request_queue->queuedata = NULL;
 		/* user context needed to free queue */
 		scsi_free_queue(sdev->request_queue);
 		/* temporary expedient, try to catch use of queue lock
@@ -343,8 +342,8 @@ static void scsi_device_dev_release_usercontext(struct work_struct *work)
 static void scsi_device_dev_release(struct device *dev)
 {
 	struct scsi_device *sdp = to_scsi_device(dev);
-	execute_in_process_context(scsi_device_dev_release_usercontext,
-				   &sdp->ew);
+
+	queue_work(scsi_wq, &sdp->release_work);
 }
 
 static struct class sdev_class = {
@@ -937,6 +936,7 @@ void __scsi_remove_device(struct scsi_device *sdev)
 	if (sdev->host->hostt->slave_destroy)
 		sdev->host->hostt->slave_destroy(sdev);
 	transport_destroy_device(dev);
+	sdev->request_queue->queuedata = NULL;
 	put_device(dev);
 }
 
@@ -1069,6 +1069,8 @@ void scsi_sysfs_device_initialize(struct scsi_device *sdev)
 	dev_set_name(&sdev->sdev_dev, "%d:%d:%d:%d",
 		     sdev->host->host_no, sdev->channel, sdev->id, sdev->lun);
 	sdev->scsi_level = starget->scsi_level;
+	INIT_WORK(&sdev->release_work, scsi_device_dev_release_usercontext);
+
 	transport_setup_device(&sdev->sdev_gendev);
 	spin_lock_irqsave(shost->host_lock, flags);
 	list_add_tail(&sdev->same_target_siblings, &starget->devices);
diff --git a/fs/gfs2/file.c b/fs/gfs2/file.c
index e483108..23eab47 100644
--- a/fs/gfs2/file.c
+++ b/fs/gfs2/file.c
@@ -545,18 +545,10 @@ static int gfs2_close(struct inode *inode, struct file *file)
 /**
  * gfs2_fsync - sync the dirty data for a file (across the cluster)
  * @file: the file that points to the dentry (we ignore this)
- * @dentry: the dentry that points to the inode to sync
+ * @datasync: set if we can ignore timestamp changes
  *
- * The VFS will flush "normal" data for us. We only need to worry
- * about metadata here. For journaled data, we just do a log flush
- * as we can't avoid it. Otherwise we can just bale out if datasync
- * is set. For stuffed inodes we must flush the log in order to
- * ensure that all data is on disk.
- *
- * The call to write_inode_now() is there to write back metadata and
- * the inode itself. It does also try and write the data, but thats
- * (hopefully) a no-op due to the VFS having already called filemap_fdatawrite()
- * for us.
+ * The VFS will flush data for us. We only need to worry
+ * about metadata here.
  *
  * Returns: errno
  */
@@ -565,22 +557,20 @@ static int gfs2_fsync(struct file *file, int datasync)
 {
 	struct inode *inode = file->f_mapping->host;
 	int sync_state = inode->i_state & (I_DIRTY_SYNC|I_DIRTY_DATASYNC);
-	int ret = 0;
-
-	if (gfs2_is_jdata(GFS2_I(inode))) {
-		gfs2_log_flush(GFS2_SB(inode), GFS2_I(inode)->i_gl);
-		return 0;
-	}
+	struct gfs2_inode *ip = GFS2_I(inode);
+	int ret;
 
-	if (sync_state != 0) {
-		if (!datasync)
-			ret = write_inode_now(inode, 0);
+	if (datasync)
+		sync_state &= ~I_DIRTY_SYNC;
 
-		if (gfs2_is_stuffed(GFS2_I(inode)))
-			gfs2_log_flush(GFS2_SB(inode), GFS2_I(inode)->i_gl);
+	if (sync_state) {
+		ret = sync_inode_metadata(inode, 1);
+		if (ret)
+			return ret;
+		gfs2_ail_flush(ip->i_gl);
 	}
 
-	return ret;
+	return 0;
 }
 
 /**
diff --git a/fs/gfs2/glops.c b/fs/gfs2/glops.c
index 25eeb2b..7c1b08f 100644
--- a/fs/gfs2/glops.c
+++ b/fs/gfs2/glops.c
@@ -28,33 +28,18 @@
 #include "trans.h"
 
 /**
- * ail_empty_gl - remove all buffers for a given lock from the AIL
+ * __gfs2_ail_flush - remove all buffers for a given lock from the AIL
  * @gl: the glock
  *
  * None of the buffers should be dirty, locked, or pinned.
  */
 
-static void gfs2_ail_empty_gl(struct gfs2_glock *gl)
+static void __gfs2_ail_flush(struct gfs2_glock *gl)
 {
 	struct gfs2_sbd *sdp = gl->gl_sbd;
 	struct list_head *head = &gl->gl_ail_list;
 	struct gfs2_bufdata *bd;
 	struct buffer_head *bh;
-	struct gfs2_trans tr;
-
-	memset(&tr, 0, sizeof(tr));
-	tr.tr_revokes = atomic_read(&gl->gl_ail_count);
-
-	if (!tr.tr_revokes)
-		return;
-
-	/* A shortened, inline version of gfs2_trans_begin() */
-	tr.tr_reserved = 1 + gfs2_struct2blk(sdp, tr.tr_revokes, sizeof(u64));
-	tr.tr_ip = (unsigned long)__builtin_return_address(0);
-	INIT_LIST_HEAD(&tr.tr_list_buf);
-	gfs2_log_reserve(sdp, tr.tr_reserved);
-	BUG_ON(current->journal_info);
-	current->journal_info = &tr;
 
 	spin_lock(&sdp->sd_ail_lock);
 	while (!list_empty(head)) {
@@ -76,7 +61,47 @@ static void gfs2_ail_empty_gl(struct gfs2_glock *gl)
 	}
 	gfs2_assert_withdraw(sdp, !atomic_read(&gl->gl_ail_count));
 	spin_unlock(&sdp->sd_ail_lock);
+}
+
+
+static void gfs2_ail_empty_gl(struct gfs2_glock *gl)
+{
+	struct gfs2_sbd *sdp = gl->gl_sbd;
+	struct gfs2_trans tr;
+
+	memset(&tr, 0, sizeof(tr));
+	tr.tr_revokes = atomic_read(&gl->gl_ail_count);
+
+	if (!tr.tr_revokes)
+		return;
+
+	/* A shortened, inline version of gfs2_trans_begin() */
+	tr.tr_reserved = 1 + gfs2_struct2blk(sdp, tr.tr_revokes, sizeof(u64));
+	tr.tr_ip = (unsigned long)__builtin_return_address(0);
+	INIT_LIST_HEAD(&tr.tr_list_buf);
+	gfs2_log_reserve(sdp, tr.tr_reserved);
+	BUG_ON(current->journal_info);
+	current->journal_info = &tr;
+
+	__gfs2_ail_flush(gl);
+
+	gfs2_trans_end(sdp);
+	gfs2_log_flush(sdp, NULL);
+}
 
+void gfs2_ail_flush(struct gfs2_glock *gl)
+{
+	struct gfs2_sbd *sdp = gl->gl_sbd;
+	unsigned int revokes = atomic_read(&gl->gl_ail_count);
+	int ret;
+
+	if (!revokes)
+		return;
+
+	ret = gfs2_trans_begin(sdp, 0, revokes);
+	if (ret)
+		return;
+	__gfs2_ail_flush(gl);
 	gfs2_trans_end(sdp);
 	gfs2_log_flush(sdp, NULL);
 }
diff --git a/fs/gfs2/glops.h b/fs/gfs2/glops.h
index b3aa2e3..6fce409 100644
--- a/fs/gfs2/glops.h
+++ b/fs/gfs2/glops.h
@@ -23,4 +23,6 @@ extern const struct gfs2_glock_operations gfs2_quota_glops;
 extern const struct gfs2_glock_operations gfs2_journal_glops;
 extern const struct gfs2_glock_operations *gfs2_glops_list[];
 
+extern void gfs2_ail_flush(struct gfs2_glock *gl);
+
 #endif /* __GLOPS_DOT_H__ */
diff --git a/include/scsi/scsi_device.h b/include/scsi/scsi_device.h
index 2d3ec50..1d11750 100644
--- a/include/scsi/scsi_device.h
+++ b/include/scsi/scsi_device.h
@@ -168,7 +168,7 @@ struct scsi_device {
 	struct device		sdev_gendev,
 				sdev_dev;
 
-	struct execute_work	ew; /* used to get process context on put */
+	struct work_struct	release_work; /* for process context on put */
 
 	struct scsi_dh_data	*scsi_dh_data;
 	enum scsi_device_state sdev_state;
@@ -259,7 +259,7 @@ struct scsi_target {
 #define SCSI_DEFAULT_TARGET_BLOCKED	3
 
 	char			scsi_level;
-	struct execute_work	ew;
+	struct work_struct	reap_work;
 	enum scsi_target_state	state;
 	void 			*hostdata; /* available to low-level driver */
 	unsigned long		starget_data[0]; /* for the transport */
@@ -277,6 +277,8 @@ static inline struct scsi_target *scsi_target(struct scsi_device *sdev)
 #define starget_printk(prefix, starget, fmt, a...)	\
 	dev_printk(prefix, &(starget)->dev, fmt, ##a)
 
+extern struct workqueue_struct *scsi_wq;
+
 extern struct scsi_device *__scsi_add_device(struct Scsi_Host *,
 		uint, uint, uint, void *hostdata);
 extern int scsi_add_device(struct Scsi_Host *host, uint channel,


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