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Subject[PATCHv5 15/15] writeback: cleanup bdi_register
Date
From: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>

This patch makes sure we first initialize everything and set the BDI_registered
flag, and only after this we add the bdi to 'bdi_list'. Current code adds the
bdi to the list too early, and as a result I the

WARN(!test_bit(BDI_registered, &bdi->state)

in bdi forker is triggered. Also, it is in general good practice to make things
visible only when they are fully initialized.

Also, this patch does few micro clean-ups:
1. Removes the 'exit' label which does not do anything, just returns. This
allows to get rid of few braces and 'ret' variable and make the code smaller.
2. If 'kthread_run()' fails, remove the error code it returns, not hard-coded
'-ENOMEM'. Theoretically, some day 'kthread_run()' can return something
else. Also, in case of failure it is not necessary to set 'bdi->wb.task' to
NULL.

Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
---
mm/backing-dev.c | 30 +++++++++++-------------------
1 files changed, 11 insertions(+), 19 deletions(-)
diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index b4d72d4..73d854b 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -511,23 +511,16 @@ int bdi_register(struct backing_dev_info *bdi, struct device *parent,
const char *fmt, ...)
{
va_list args;
- int ret = 0;
struct device *dev;

if (bdi->dev) /* The driver needs to use separate queues per device */
- goto exit;
+ return 0;

va_start(args, fmt);
dev = device_create_vargs(bdi_class, parent, MKDEV(0, 0), bdi, fmt, args);
va_end(args);
- if (IS_ERR(dev)) {
- ret = PTR_ERR(dev);
- goto exit;
- }
-
- spin_lock_bh(&bdi_lock);
- list_add_tail_rcu(&bdi->bdi_list, &bdi_list);
- spin_unlock_bh(&bdi_lock);
+ if (IS_ERR(dev))
+ return PTR_ERR(dev);

bdi->dev = dev;

@@ -541,20 +534,19 @@ int bdi_register(struct backing_dev_info *bdi, struct device *parent,

wb->task = kthread_run(bdi_forker_thread, wb, "bdi-%s",
dev_name(dev));
- if (IS_ERR(wb->task)) {
- wb->task = NULL;
- ret = -ENOMEM;
-
- bdi_remove_from_list(bdi);
- goto exit;
- }
+ if (IS_ERR(wb->task))
+ return PTR_ERR(wb->task);
}

bdi_debug_register(bdi, dev_name(dev));
set_bit(BDI_registered, &bdi->state);
+
+ spin_lock_bh(&bdi_lock);
+ list_add_tail_rcu(&bdi->bdi_list, &bdi_list);
+ spin_unlock_bh(&bdi_lock);
+
trace_writeback_bdi_register(bdi);
-exit:
- return ret;
+ return 0;
}
EXPORT_SYMBOL(bdi_register);

--
1.7.1.1


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