From: Christoph Hellwig <hch@lst.de>

BugLink: http://bugs.launchpad.net/bugs/585092

commit 7f0e7bed936a0c422641a046551829a01341dd80 upstream

The code dealing with bdi_work->state and completion of a bdi_work is a
major mess currently. This patch makes sure we directly use one set of
flags to deal with it, and use it consistently, which means:

- always notify about completion from the rcu callback. We only ever
wait for it from on-stack callers, so this simplification does not
even cause a theoretical slowdown currently. It also makes sure we
don't miss out on the notification if we ever add other callers to
wait for it.
- make earlier completion notification depending on the on-stack
allocation, not the sync mode. If we introduce new callers that
want to do WB_SYNC_NONE writeback from on-stack callers this will
be nessecary.

Also rename bdi_wait_on_work_clear to bdi_wait_on_work_done and inline
a few small functions into their only caller to make the code
understandable.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
---
fs/fs-writeback.c | 65 ++++++++++++----------------------------------------
1 files changed, 15 insertions(+), 50 deletions(-)

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 478dec1..1538e44 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -62,24 +62,16 @@ struct bdi_work {
};

enum {
- WS_USED_B = 0,
- WS_ONSTACK_B,
+ WS_INPROGRESS = 0,
+ WS_ONSTACK,
};

-#define WS_USED (1 << WS_USED_B)
-#define WS_ONSTACK (1 << WS_ONSTACK_B)
-
-static inline bool bdi_work_on_stack(struct bdi_work *work)
-{
- return test_bit(WS_ONSTACK_B, &work->state);
-}
-
static inline void bdi_work_init(struct bdi_work *work,
struct wb_writeback_args *args)
{
INIT_RCU_HEAD(&work->rcu_head);
work->args = *args;
- work->state = WS_USED;
+ __set_bit(WS_INPROGRESS, &work->state);
}

/**
@@ -94,43 +86,16 @@ int writeback_in_progress(struct backing_dev_info *bdi)
return !list_empty(&bdi->work_list);
}

-static void bdi_work_clear(struct bdi_work *work)
-{
- clear_bit(WS_USED_B, &work->state);
- smp_mb__after_clear_bit();
- /*
- * work can have disappeared at this point. bit waitq functions
- * should be able to tolerate this, provided bdi_sched_wait does
- * not dereference it's pointer argument.
- */
- wake_up_bit(&work->state, WS_USED_B);
-}
-
static void bdi_work_free(struct rcu_head *head)
{
struct bdi_work *work = container_of(head, struct bdi_work, rcu_head);

- if (!bdi_work_on_stack(work))
- kfree(work);
- else
- bdi_work_clear(work);
-}
-
-static void wb_work_complete(struct bdi_work *work)
-{
- const enum writeback_sync_modes sync_mode = work->args.sync_mode;
- int onstack = bdi_work_on_stack(work);
+ clear_bit(WS_INPROGRESS, &work->state);
+ smp_mb__after_clear_bit();
+ wake_up_bit(&work->state, WS_INPROGRESS);

- /*
- * For allocated work, we can clear the done/seen bit right here.
- * For on-stack work, we need to postpone both the clear and free
- * to after the RCU grace period, since the stack could be invalidated
- * as soon as bdi_work_clear() has done the wakeup.
- */
- if (!onstack)
- bdi_work_clear(work);
- if (sync_mode == WB_SYNC_NONE || onstack)
- call_rcu(&work->rcu_head, bdi_work_free);
+ if (!test_bit(WS_ONSTACK, &work->state))
+ kfree(work);
}

static void wb_clear_pending(struct bdi_writeback *wb, struct bdi_work *work)
@@ -146,7 +111,7 @@ static void wb_clear_pending(struct bdi_writeback *wb, struct bdi_work *work)
list_del_rcu(&work->list);
spin_unlock(&bdi->wb_lock);

- wb_work_complete(work);
+ call_rcu(&work->rcu_head, bdi_work_free);
}
}

@@ -184,9 +149,9 @@ static void bdi_queue_work(struct backing_dev_info *bdi, struct bdi_work *work)
* Used for on-stack allocated work items. The caller needs to wait until
* the wb threads have acked the work before it's safe to continue.
*/
-static void bdi_wait_on_work_clear(struct bdi_work *work)
+static void bdi_wait_on_work_done(struct bdi_work *work)
{
- wait_on_bit(&work->state, WS_USED_B, bdi_sched_wait,
+ wait_on_bit(&work->state, WS_INPROGRESS, bdi_sched_wait,
TASK_UNINTERRUPTIBLE);
}

@@ -233,10 +198,10 @@ static void bdi_sync_writeback(struct backing_dev_info *bdi,
struct bdi_work work;

bdi_work_init(&work, &args);
- work.state |= WS_ONSTACK;
+ __set_bit(WS_ONSTACK, &work.state);

bdi_queue_work(bdi, &work);
- bdi_wait_on_work_clear(&work);
+ bdi_wait_on_work_done(&work);
}

/**
@@ -898,7 +863,7 @@ long wb_do_writeback(struct bdi_writeback *wb, int force_wait)
* If this isn't a data integrity operation, just notify
* that we have seen this work and we are now starting it.
*/
- if (args.sync_mode == WB_SYNC_NONE)
+ if (!test_bit(WS_ONSTACK, &work->state))
wb_clear_pending(wb, work);

wrote += wb_writeback(wb, &args);
@@ -907,7 +872,7 @@ long wb_do_writeback(struct bdi_writeback *wb, int force_wait)
* This is a data integrity writeback, so only do the
* notification when we have completed the work.
*/
- if (args.sync_mode == WB_SYNC_ALL)
+ if (test_bit(WS_ONSTACK, &work->state))
wb_clear_pending(wb, work);
}

--
1.7.0.4


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