From: Joe Thornber <ejt@redhat.com>
Date: Fri, 10 Oct 2014 14:27:16 +0000 (+0100)
Subject: dm thin: remap the bios in a cell immediately
X-Git-Tag: omap-for-v3.19/fixes-for-merge-window~22^2~35
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=2d759a46b4d65e1392843cf9df7101897af87008;p=pandora-kernel.git

dm thin: remap the bios in a cell immediately

This use of direct submission in process_prepared_mapping() reduces
latency for submitting bios in a cell by avoiding adding those bios to
the deferred list and waiting for the next iteration of the worker.

But this direct submission exposes the potential for a race between
releasing a cell and incrementing deferred set.  Fix this by introducing
dm_cell_visit_release() and refactoring inc_remap_and_issue_cell()
accordingly.

Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
---

diff --git a/drivers/md/dm-bio-prison.c b/drivers/md/dm-bio-prison.c
index 90a56625245a..bbe22a5dc06b 100644
--- a/drivers/md/dm-bio-prison.c
+++ b/drivers/md/dm-bio-prison.c
@@ -241,6 +241,20 @@ void dm_cell_error(struct dm_bio_prison *prison,
 }
 EXPORT_SYMBOL_GPL(dm_cell_error);
 
+void dm_cell_visit_release(struct dm_bio_prison *prison,
+			   void (*visit_fn)(void *, struct dm_bio_prison_cell *),
+			   void *context,
+			   struct dm_bio_prison_cell *cell)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&prison->lock, flags);
+	visit_fn(context, cell);
+	rb_erase(&cell->node, &prison->cells);
+	spin_unlock_irqrestore(&prison->lock, flags);
+}
+EXPORT_SYMBOL_GPL(dm_cell_visit_release);
+
 /*----------------------------------------------------------------*/
 
 #define DEFERRED_SET_SIZE 64
diff --git a/drivers/md/dm-bio-prison.h b/drivers/md/dm-bio-prison.h
index c0cddb118582..b03988667740 100644
--- a/drivers/md/dm-bio-prison.h
+++ b/drivers/md/dm-bio-prison.h
@@ -89,6 +89,14 @@ void dm_cell_release_no_holder(struct dm_bio_prison *prison,
 void dm_cell_error(struct dm_bio_prison *prison,
 		   struct dm_bio_prison_cell *cell, int error);
 
+/*
+ * Visits the cell and then releases.  Guarantees no new inmates are
+ * inserted between the visit and release.
+ */
+void dm_cell_visit_release(struct dm_bio_prison *prison,
+			   void (*visit_fn)(void *, struct dm_bio_prison_cell *),
+			   void *context, struct dm_bio_prison_cell *cell);
+
 /*----------------------------------------------------------------*/
 
 /*
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