From: Madhuparna Bhowmik madhuparnabhowmik10@gmail.com
hlist_for_each_entry_rcu() has built-in RCU and lock checking.
Pass cond argument to hlist_for_each_entry_rcu() to silence false lockdep warnings when CONFIG_PROVE_RCU_LIST is enabled by default.
Signed-off-by: Madhuparna Bhowmik madhuparnabhowmik10@gmail.com --- net/batman-adv/translation-table.c | 12 ++++++++---- 1 file changed, 8 insertions(+), 4 deletions(-)
diff --git a/net/batman-adv/translation-table.c b/net/batman-adv/translation-table.c index 8a482c5ec67b..0e3c31cbe0e8 100644 --- a/net/batman-adv/translation-table.c +++ b/net/batman-adv/translation-table.c @@ -862,7 +862,8 @@ batadv_tt_prepare_tvlv_global_data(struct batadv_orig_node *orig_node, u8 *tt_change_ptr;
spin_lock_bh(&orig_node->vlan_list_lock); - hlist_for_each_entry_rcu(vlan, &orig_node->vlan_list, list) { + hlist_for_each_entry_rcu(vlan, &orig_node->vlan_list, list, + lockdep_is_held(&orig_node->vlan_list_lock)) { num_vlan++; num_entries += atomic_read(&vlan->tt.num_entries); } @@ -888,7 +889,8 @@ batadv_tt_prepare_tvlv_global_data(struct batadv_orig_node *orig_node, (*tt_data)->num_vlan = htons(num_vlan);
tt_vlan = (struct batadv_tvlv_tt_vlan_data *)(*tt_data + 1); - hlist_for_each_entry_rcu(vlan, &orig_node->vlan_list, list) { + hlist_for_each_entry_rcu(vlan, &orig_node->vlan_list, list, + lockdep_is_held(&orig_node->vlan_list_lock)) { tt_vlan->vid = htons(vlan->vid); tt_vlan->crc = htonl(vlan->tt.crc);
@@ -937,7 +939,8 @@ batadv_tt_prepare_tvlv_local_data(struct batadv_priv *bat_priv, int change_offset;
spin_lock_bh(&bat_priv->softif_vlan_list_lock); - hlist_for_each_entry_rcu(vlan, &bat_priv->softif_vlan_list, list) { + hlist_for_each_entry_rcu(vlan, &bat_priv->softif_vlan_list, list, + lockdep_is_held(&bat_priv->softif_vlan_list_lock)) { vlan_entries = atomic_read(&vlan->tt.num_entries); if (vlan_entries < 1) continue; @@ -967,7 +970,8 @@ batadv_tt_prepare_tvlv_local_data(struct batadv_priv *bat_priv, (*tt_data)->num_vlan = htons(num_vlan);
tt_vlan = (struct batadv_tvlv_tt_vlan_data *)(*tt_data + 1); - hlist_for_each_entry_rcu(vlan, &bat_priv->softif_vlan_list, list) { + hlist_for_each_entry_rcu(vlan, &bat_priv->softif_vlan_list, list, + lockdep_is_held(&bat_priv->softif_vlan_list_lock)) { vlan_entries = atomic_read(&vlan->tt.num_entries); if (vlan_entries < 1) continue;
On Sunday, 16 February 2020 15:47:18 CET madhuparnabhowmik10@gmail.com wrote:
From: Madhuparna Bhowmik madhuparnabhowmik10@gmail.com
hlist_for_each_entry_rcu() has built-in RCU and lock checking.
Pass cond argument to hlist_for_each_entry_rcu() to silence false lockdep warnings when CONFIG_PROVE_RCU_LIST is enabled by default.
Signed-off-by: Madhuparna Bhowmik madhuparnabhowmik10@gmail.com
net/batman-adv/translation-table.c | 12 ++++++++---- 1 file changed, 8 insertions(+), 4 deletions(-)
Added with alignment and line length codingstyle fixes [1].
Can you tell us how you've identified these four hlist_for_each_entry_rcu?
Thanks, Sven
[1] https://git.open-mesh.org/linux-merge.git/commit/967709ec53a07d1bccbc3716f7e...
On Sun, Feb 16, 2020 at 04:22:51PM +0100, Sven Eckelmann wrote:
On Sunday, 16 February 2020 15:47:18 CET madhuparnabhowmik10@gmail.com wrote:
From: Madhuparna Bhowmik madhuparnabhowmik10@gmail.com
hlist_for_each_entry_rcu() has built-in RCU and lock checking.
Pass cond argument to hlist_for_each_entry_rcu() to silence false lockdep warnings when CONFIG_PROVE_RCU_LIST is enabled by default.
Signed-off-by: Madhuparna Bhowmik madhuparnabhowmik10@gmail.com
net/batman-adv/translation-table.c | 12 ++++++++---- 1 file changed, 8 insertions(+), 4 deletions(-)
Added with alignment and line length codingstyle fixes [1].
Can you tell us how you've identified these four hlist_for_each_entry_rcu?
Hi Sven,
Thank you for the fixes. The other hlist_for_each_entry_rcu() are used under the protection of rcu_read_lock(). We only need to pass the cond when hlist_for_each_entry_rcu() is used under a different lock (not under rcu_red_lock()) because according to the current scheme a lockdep splat is generated when hlist_for_each_entry_rcu() is used outside of rcu_read_lock() or the lockdep condition (the cond argument) evaluates to false. So, we need to pass this cond when it is used under the protection of spinlock or mutex etc. and not required if rcu_read_lock() is used.
Thank you, Madhuparna
Thanks, Sven
[1] https://git.open-mesh.org/linux-merge.git/commit/967709ec53a07d1bccbc3716f7e...
On Sunday, 16 February 2020 16:33:24 CET Madhuparna Bhowmik wrote: [...]
Can you tell us how you've identified these four hlist_for_each_entry_rcu?
The other hlist_for_each_entry_rcu() are used under the protection of rcu_read_lock(). We only need to pass the cond when hlist_for_each_entry_rcu() is used under a different lock (not under rcu_red_lock()) because according to the current scheme a lockdep splat is generated when hlist_for_each_entry_rcu() is used outside of rcu_read_lock() or the lockdep condition (the cond argument) evaluates to false. So, we need to pass this cond when it is used under the protection of spinlock or mutex etc. and not required if rcu_read_lock() is used.
I understand this part. I was asking how you've identified them. Did you use any tool for that? coccinelle, sparse, ...
Kind regards, Sven
On Sun, Feb 16, 2020 at 04:35:54PM +0100, Sven Eckelmann wrote:
On Sunday, 16 February 2020 16:33:24 CET Madhuparna Bhowmik wrote: [...]
Can you tell us how you've identified these four hlist_for_each_entry_rcu?
The other hlist_for_each_entry_rcu() are used under the protection of rcu_read_lock(). We only need to pass the cond when hlist_for_each_entry_rcu() is used under a different lock (not under rcu_red_lock()) because according to the current scheme a lockdep splat is generated when hlist_for_each_entry_rcu() is used outside of rcu_read_lock() or the lockdep condition (the cond argument) evaluates to false. So, we need to pass this cond when it is used under the protection of spinlock or mutex etc. and not required if rcu_read_lock() is used.
I understand this part. I was asking how you've identified them. Did you use any tool for that? coccinelle, sparse, ...
Hi,
Not really, I did it manually by inspecting each occurence. Thank you, Madhuparna
Kind regards, Sven
On Sunday, 16 February 2020 16:52:44 CET Madhuparna Bhowmik wrote: [...]
I understand this part. I was asking how you've identified them. Did you use any tool for that? coccinelle, sparse, ...
Not really, I did it manually by inspecting each occurence.
In that case, I don't understand why you didn't convert the occurrences from hlist_for_each_entry_rcu to hlist_for_each_entry [1]. Because a manual inspection should have noticed that there will always be the lock around these ones.
KInd regards, Sven
[1] https://www.kernel.org/doc/html/v5.6-rc1/RCU/whatisRCU.html#analogy-with-rea...
On Sun, Feb 16, 2020 at 05:17:36PM +0100, Sven Eckelmann wrote:
On Sunday, 16 February 2020 16:52:44 CET Madhuparna Bhowmik wrote: [...]
I understand this part. I was asking how you've identified them. Did you use any tool for that? coccinelle, sparse, ...
Not really, I did it manually by inspecting each occurence.
In that case, I don't understand why you didn't convert the occurrences from hlist_for_each_entry_rcu to hlist_for_each_entry [1]. Because a manual inspection should have noticed that there will always be the lock around these ones.
Hi Sven, I have been working on similar issues (passing cond argument to list_for_each_entry_Rcu()). That's why may be I didn't notice that in this case rcu variant is not required. Thank you for taking a closer look and fixing it the right way.
Regards, Madhuparna
KInd regards, Sven
[1] https://www.kernel.org/doc/html/v5.6-rc1/RCU/whatisRCU.html#analogy-with-rea...
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Sven Eckelmann