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| author | Usama Arif <usama.arif@linux.dev> | 2026-05-21 03:29:26 -0700 |
|---|---|---|
| committer | Steffen Klassert <steffen.klassert@secunet.com> | 2026-05-26 10:35:29 +0200 |
| commit | 3e52417318473782012b236d0325bf7d2266a597 (patch) | |
| tree | 74560d95539d4cc8081012ebd025235218021db6 /net | |
| parent | 7f83d174073234839aea176f265e517e0d50a1d2 (diff) | |
| download | linux-next-history-3e52417318473782012b236d0325bf7d2266a597.tar.gz | |
xfrm: move policy_bydst RCU sync from per-netns .exit to .pre_exit
The struct pernet_operations docstring in include/net/net_namespace.h
explicitly warns against blocking RCU primitives in .exit handlers:
Exit methods using blocking RCU primitives, such as
synchronize_rcu(), should be implemented via exit_batch.
[...]
Please, avoid synchronize_rcu() at all, where it's possible.
Note that a combination of pre_exit() and exit() can
be used, since a synchronize_rcu() is guaranteed between
the calls.
xfrm_policy_fini() violates this: it calls synchronize_rcu() before
freeing the policy_bydst hash tables (so no RCU reader is mid-
traversal at free time), but runs from xfrm_net_ops.exit -- once per
namespace -- so a cleanup_net() of N namespaces pays N full RCU
grace periods serially.
Use the documented pre_exit/exit split. Move the policy flush (and
the workqueue drains it depends on) into a new .pre_exit handler;
xfrm_policy_fini() then runs in .exit and frees the hash tables
after the synchronize_rcu_expedited() that cleanup_net() guarantees
between the two phases. Providing O(1) RCU grace periods per batch
instead of O(N).
Observed on Linux 6.18 with a workload doing unshare(CLONE_NEWNET)
at ~13/sec sustained: cleanup_net() and the netns_wq rescuer kthread
both stuck in xfrm_policy_fini()'s synchronize_rcu(), >300k struct
net accumulated in the cleanup queue, Percpu in /proc/meminfo climbed
to 130+ GB on 256-CPU hosts, and memcg OOMs followed. setup_net and
__put_net counts were balanced, ruling out a refcount leak.
Fixes: 069daad4f2ae ("xfrm: Wait for RCU readers during policy netns exit")
Signed-off-by: Usama Arif <usama.arif@linux.dev>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
Diffstat (limited to 'net')
| -rw-r--r-- | net/xfrm/xfrm_policy.c | 15 |
1 files changed, 8 insertions, 7 deletions
diff --git a/net/xfrm/xfrm_policy.c b/net/xfrm/xfrm_policy.c index 59968dcbafe1f..dd09d2063da2d 100644 --- a/net/xfrm/xfrm_policy.c +++ b/net/xfrm/xfrm_policy.c @@ -4276,21 +4276,21 @@ out_byidx: return -ENOMEM; } -static void xfrm_policy_fini(struct net *net) +static void __net_exit xfrm_net_pre_exit(struct net *net) { - struct xfrm_pol_inexact_bin *b, *t; - unsigned int sz; - int dir; - disable_work_sync(&net->xfrm.policy_hthresh.work); - flush_work(&net->xfrm.policy_hash_work); #ifdef CONFIG_XFRM_SUB_POLICY xfrm_policy_flush(net, XFRM_POLICY_TYPE_SUB, false); #endif xfrm_policy_flush(net, XFRM_POLICY_TYPE_MAIN, false); +} - synchronize_rcu(); +static void xfrm_policy_fini(struct net *net) +{ + struct xfrm_pol_inexact_bin *b, *t; + unsigned int sz; + int dir; WARN_ON(!list_empty(&net->xfrm.policy_all)); @@ -4368,6 +4368,7 @@ static void __net_exit xfrm_net_exit(struct net *net) static struct pernet_operations __net_initdata xfrm_net_ops = { .init = xfrm_net_init, + .pre_exit = xfrm_net_pre_exit, .exit = xfrm_net_exit, }; |