From: Madhuparna Bhowmik <[email protected]>
list_for_each_entry_rcu has built-in RCU and lock checking.
Pass cond argument to list_for_each_entry_rcu.
Signed-off-by: Madhuparna Bhowmik <[email protected]>
---
drivers/net/xen-netback/hash.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/drivers/net/xen-netback/hash.c b/drivers/net/xen-netback/hash.c
index 10d580c3dea3..30709bc9d170 100644
--- a/drivers/net/xen-netback/hash.c
+++ b/drivers/net/xen-netback/hash.c
@@ -51,7 +51,8 @@ static void xenvif_add_hash(struct xenvif *vif, const u8 *tag,
found = false;
oldest = NULL;
- list_for_each_entry_rcu(entry, &vif->hash.cache.list, link) {
+ list_for_each_entry_rcu(entry, &vif->hash.cache.list, link,
+ lockdep_is_held(&vif->hash.cache.lock)) {
/* Make sure we don't add duplicate entries */
if (entry->len == len &&
memcmp(entry->tag, tag, len) == 0)
@@ -102,7 +103,8 @@ static void xenvif_flush_hash(struct xenvif *vif)
spin_lock_irqsave(&vif->hash.cache.lock, flags);
- list_for_each_entry_rcu(entry, &vif->hash.cache.list, link) {
+ list_for_each_entry_rcu(entry, &vif->hash.cache.list, link,
+ lockdep_is_held(&vif->hash.cache.lock)) {
list_del_rcu(&entry->link);
vif->hash.cache.count--;
kfree_rcu(entry, rcu);
--
2.17.1
Thanks for the patch.
There is a typo in the subject line. It should say xen-netback, not
xen-netbank.
On Wed, Jan 15, 2020 at 06:11:28PM +0530, [email protected] wrote:
> From: Madhuparna Bhowmik <[email protected]>
>
> list_for_each_entry_rcu has built-in RCU and lock checking.
> Pass cond argument to list_for_each_entry_rcu.
>
> Signed-off-by: Madhuparna Bhowmik <[email protected]>
> ---
> drivers/net/xen-netback/hash.c | 6 ++++--
> 1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/net/xen-netback/hash.c b/drivers/net/xen-netback/hash.c
> index 10d580c3dea3..30709bc9d170 100644
> --- a/drivers/net/xen-netback/hash.c
> +++ b/drivers/net/xen-netback/hash.c
> @@ -51,7 +51,8 @@ static void xenvif_add_hash(struct xenvif *vif, const u8 *tag,
>
> found = false;
> oldest = NULL;
> - list_for_each_entry_rcu(entry, &vif->hash.cache.list, link) {
> + list_for_each_entry_rcu(entry, &vif->hash.cache.list, link,
> + lockdep_is_held(&vif->hash.cache.lock)) {
There are probably too many tabs here. Indentation looks wrong.
The surrounding code makes it pretty clear that the lock is already held
by the time list_for_each_entry_rcu is called, yet the checking involved
in lockdep_is_held is not trivial, so I'm afraid I don't consider this a
strict improvement over the existing code.
If there is something I misunderstood, let me know.
Wei.
> /* Make sure we don't add duplicate entries */
> if (entry->len == len &&
> memcmp(entry->tag, tag, len) == 0)
> @@ -102,7 +103,8 @@ static void xenvif_flush_hash(struct xenvif *vif)
>
> spin_lock_irqsave(&vif->hash.cache.lock, flags);
>
> - list_for_each_entry_rcu(entry, &vif->hash.cache.list, link) {
> + list_for_each_entry_rcu(entry, &vif->hash.cache.list, link,
> + lockdep_is_held(&vif->hash.cache.lock)) {
> list_del_rcu(&entry->link);
> vif->hash.cache.count--;
> kfree_rcu(entry, rcu);
> --
> 2.17.1
>
On Wed, Jan 15, 2020 at 07:36:38PM +0530, Madhuparna Bhowmik wrote:
[...]
>
> > The surrounding code makes it pretty clear that the lock is already held
> > by the time list_for_each_entry_rcu is called, yet the checking involved
> > in lockdep_is_held is not trivial, so I'm afraid I don't consider this a
> > strict improvement over the existing code.
> >
> > Actually, we want to make CONFIG_PROVE_LIST_RCU enabled by default.
I think you meant CONFIG_PROVE_RCU_LIST.
> And if the cond argument is not passed when the usage of
> list_for_each_entry_rcu()
> is outside of rcu_read_lock(), it will lead to a false positive.
> Therefore, I think this patch is required.
Fair enough.
Wei.