diff mbox series

[net-next] net: avoid quadratic behavior in netdev_wait_allrefs_any()

Message ID 20220218065430.2613262-1-eric.dumazet@gmail.com (mailing list archive)
State Accepted
Commit 86213f80da1b1d007721cc22e04b5f5d0da33127
Delegated to: Netdev Maintainers
Headers show
Series [net-next] net: avoid quadratic behavior in netdev_wait_allrefs_any() | expand

Checks

Context Check Description
netdev/tree_selection success Clearly marked for net-next
netdev/fixes_present success Fixes tag not required for -next series
netdev/subject_prefix success Link
netdev/cover_letter success Single patches do not need cover letters
netdev/patch_count success Link
netdev/header_inline success No static functions without inline keyword in header files
netdev/build_32bit success Errors and warnings before: 9 this patch: 9
netdev/cc_maintainers fail 1 blamed authors not CCed: lucien.xin@gmail.com; 1 maintainers not CCed: lucien.xin@gmail.com
netdev/build_clang success Errors and warnings before: 18 this patch: 18
netdev/module_param success Was 0 now: 0
netdev/verify_signedoff success Signed-off-by tag matches author and committer
netdev/verify_fixes success Fixes tag looks correct
netdev/build_allmodconfig_warn success Errors and warnings before: 14 this patch: 14
netdev/checkpatch success total: 0 errors, 0 warnings, 0 checks, 16 lines checked
netdev/kdoc success Errors and warnings before: 0 this patch: 0
netdev/source_inline success Was 0 now: 0

Commit Message

Eric Dumazet Feb. 18, 2022, 6:54 a.m. UTC 
From: Eric Dumazet <edumazet@google.com>

If the list of devices has N elements, netdev_wait_allrefs_any()
is called N times, and linkwatch_forget_dev() is called N*(N-1)/2 times.

Fix this by calling linkwatch_forget_dev() only once per device.

Fixes: faab39f63c1f ("net: allow out-of-order netdev unregistration")
Signed-off-by: Eric Dumazet <edumazet@google.com>
---
 net/core/dev.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

Comments

Jakub Kicinski Feb. 18, 2022, 3:28 p.m. UTC | #1 
On Thu, 17 Feb 2022 22:54:30 -0800 Eric Dumazet wrote:
> From: Eric Dumazet <edumazet@google.com>
> 
> If the list of devices has N elements, netdev_wait_allrefs_any()
> is called N times, and linkwatch_forget_dev() is called N*(N-1)/2 times.
> 
> Fix this by calling linkwatch_forget_dev() only once per device.
> 
> Fixes: faab39f63c1f ("net: allow out-of-order netdev unregistration")
> Signed-off-by: Eric Dumazet <edumazet@google.com>

Yup, I was on the fence on this one, I went for keeping all linkwatch
stuff in one function and minimal changes. Clearly underestimated the
number of netdevs your cases are destroying at once :)
patchwork-bot+netdevbpf@kernel.org Feb. 18, 2022, 3:40 p.m. UTC | #2 
Hello:

This patch was applied to netdev/net-next.git (master)
by Jakub Kicinski <kuba@kernel.org>:

On Thu, 17 Feb 2022 22:54:30 -0800 you wrote:
> From: Eric Dumazet <edumazet@google.com>
> 
> If the list of devices has N elements, netdev_wait_allrefs_any()
> is called N times, and linkwatch_forget_dev() is called N*(N-1)/2 times.
> 
> Fix this by calling linkwatch_forget_dev() only once per device.
> 
> [...]

Here is the summary with links:
  - [net-next] net: avoid quadratic behavior in netdev_wait_allrefs_any()
    https://git.kernel.org/netdev/net-next/c/86213f80da1b

You are awesome, thank you!
diff mbox series

Patch

diff --git a/net/core/dev.c b/net/core/dev.c
index 05fa867f18787e709dcaccfea1df350c424eff80..acd884910e12a040841e1e0525e0d4bc5e3ee799 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -9828,9 +9828,6 @@  static struct net_device *netdev_wait_allrefs_any(struct list_head *list)
 	struct net_device *dev;
 	int wait = 0;
 
-	list_for_each_entry(dev, list, todo_list)
-		linkwatch_forget_dev(dev);
-
 	rebroadcast_time = warning_time = jiffies;
 
 	list_for_each_entry(dev, list, todo_list)
@@ -9951,6 +9948,7 @@  void netdev_run_todo(void)
 		}
 
 		dev->reg_state = NETREG_UNREGISTERED;
+		linkwatch_forget_dev(dev);
 	}
 
 	while (!list_empty(&list)) {