[PATCH] tux3: Use system_long_wq instead of kernel_bdi_wq

[Dongsu Park]

From: Dongsu Park <dongsu.park at profitbricks.com>

Using kallsyms_lookup_name() for looking up bdi_wq doesn't look like
a good idea. Because kallsyms_lookup_name("bdi_wq") returns NULL, when
CONFIG_KALLSYMS_ALL is not configured in the kernel. That results in
the whole filesystem being unable to be mounted. Given that not every
kernel is configured with CONFIG_KALLSYMS_ALL, that kind of hack will
not always work.

Moreover, it does not look necessary at all, to manage its own workqueue
kernel_bdi_wq. It's just enough to queue a work item to system_long_wq.

Cc: Daniel Phillips <daniel at phunq.net>
Cc: OGAWA Hirofumi <hirofumi at mail.parknet.co.jp>
Signed-off-by: Dongsu Park <dongsu.park at profitbricks.com>
---
 fs/tux3/commit_flusher_hack.c | 18 +-----------------
 1 file changed, 1 insertion(+), 17 deletions(-)

diff --git a/fs/tux3/commit_flusher_hack.c b/fs/tux3/commit_flusher_hack.c
index 08696edccf26..dfd1c799207d 100644
--- a/fs/tux3/commit_flusher_hack.c
+++ b/fs/tux3/commit_flusher_hack.c
@@ -275,9 +275,6 @@ static long tux3_do_writeback(struct bdi_writeback *wb)
 	return wrote;
 }
 
-/* Dirty hack to get bdi_wq address from module */
-static struct workqueue_struct *kernel_bdi_wq;
-
 /*
  * Handle writeback of dirty data for the device backed by this bdi. Also
  * reschedules periodically and does kupdated style flushing.
@@ -326,7 +323,7 @@ static void tux3_writeback_workfn(struct work_struct *work)
 #endif
 	if (!list_empty(&bdi->work_list) ||
 	    (wb_has_dirty_io(wb) && dirty_writeback_interval))
-		queue_delayed_work(kernel_bdi_wq, &wb->dwork,
+		queue_delayed_work(system_long_wq, &wb->dwork,
 			msecs_to_jiffies(dirty_writeback_interval * 10));
 
 	current->flags &= ~PF_SWAPWRITE;
@@ -335,19 +332,6 @@ static void tux3_writeback_workfn(struct work_struct *work)
 #include <linux/kallsyms.h>
 static int tux3_setup_writeback(struct sb *sb, struct backing_dev_info *bdi)
 {
-	/* Dirty hack to get bdi_wq address from module */
-	if (kernel_bdi_wq == NULL) {
-		unsigned long wq_addr;
-
-		wq_addr = kallsyms_lookup_name("bdi_wq");
-		if (!wq_addr) {
-			tux3_err(sb, "couldn't find bdi_wq address\n");
-			return -EINVAL;
-		}
-		kernel_bdi_wq = *(struct workqueue_struct **)wq_addr;
-		tux3_msg(sb, "use bdi_wq %p", kernel_bdi_wq);
-	}
-
 	/* Overwrite callback by ourself handler */
 	INIT_DELAYED_WORK(&bdi->wb.dwork, tux3_writeback_workfn);
 
-- 
1.9.1