[PATCH v2 2/2] libnvdimm/badrange: eliminate a meaningless spinlock operation

From: Zhen Lei
Date: Sat Sep 19 2020 - 06:46:57 EST


badrange_add() take the lock "badrange->lock", but it's released
immediately in add_badrange(), protect nothing.

The pseudo code is as follows:
In badrange_add():
spin_lock(&badrange->lock); <---------------
rc = add_badrange(badrange, addr, length); |
In add_badrange(): |
//do nothing |
spin_unlock(&badrange->lock); <---------------
bre_new = kzalloc(sizeof(*bre_new), GFP_KERNEL);
spin_lock(&badrange->lock); <--- lock again

This lock/unlock operation is meaningless.

Because the static function add_badrange() is only called by
badrange_add(), so move its content into badrange_add() then delete it.
By the way, move "kfree(bre_new)" out of the lock protection, it really
doesn't need.

Fixes: b3b454f694db ("libnvdimm: fix clear poison locking with spinlock ...")
Signed-off-by: Zhen Lei <thunder.leizhen@xxxxxxxxxx>
---
drivers/nvdimm/badrange.c | 22 ++++++++--------------
1 file changed, 8 insertions(+), 14 deletions(-)

diff --git a/drivers/nvdimm/badrange.c b/drivers/nvdimm/badrange.c
index 9fdba8c43e8605e..7f78b659057902d 100644
--- a/drivers/nvdimm/badrange.c
+++ b/drivers/nvdimm/badrange.c
@@ -45,12 +45,12 @@ static int alloc_and_append_badrange_entry(struct badrange *badrange,
return 0;
}

-static int add_badrange(struct badrange *badrange, u64 addr, u64 length)
+int badrange_add(struct badrange *badrange, u64 addr, u64 length)
{
struct badrange_entry *bre, *bre_new;

- spin_unlock(&badrange->lock);
bre_new = kzalloc(sizeof(*bre_new), GFP_KERNEL);
+
spin_lock(&badrange->lock);

/*
@@ -63,6 +63,7 @@ static int add_badrange(struct badrange *badrange, u64 addr, u64 length)
/* If length has changed, update this list entry */
if (bre->length != length)
bre->length = length;
+ spin_unlock(&badrange->lock);
kfree(bre_new);
return 0;
}
@@ -72,22 +73,15 @@ static int add_badrange(struct badrange *badrange, u64 addr, u64 length)
* as any overlapping ranges will get resolved when the list is consumed
* and converted to badblocks
*/
- if (!bre_new)
+ if (!bre_new) {
+ spin_unlock(&badrange->lock);
return -ENOMEM;
- append_badrange_entry(badrange, bre_new, addr, length);
-
- return 0;
-}
-
-int badrange_add(struct badrange *badrange, u64 addr, u64 length)
-{
- int rc;
+ }

- spin_lock(&badrange->lock);
- rc = add_badrange(badrange, addr, length);
+ append_badrange_entry(badrange, bre_new, addr, length);
spin_unlock(&badrange->lock);

- return rc;
+ return 0;
}
EXPORT_SYMBOL_GPL(badrange_add);

--
1.8.3