From e9b4ad8406696f94e1140a82ee7b035df749ab53 Mon Sep 17 00:00:00 2001 From: "Srivatsa S. Bhat" Date: Fri, 14 Feb 2014 12:13:38 +0530 Subject: [PATCH] net/core/flow.c: Fix CPU hotplug callback registration Subsystems that want to register CPU hotplug callbacks, as well as perform initialization for the CPUs that are already online, often do it as shown below: get_online_cpus(); for_each_online_cpu(cpu) init_cpu(cpu); register_cpu_notifier(&foobar_cpu_notifier); put_online_cpus(); This is wrong, since it is prone to ABBA deadlocks involving the cpu_add_remove_lock and the cpu_hotplug.lock (when running concurrently with CPU hotplug operations). Instead, the correct and race-free way of performing the callback registration is: cpu_notifier_register_begin(); for_each_online_cpu(cpu) init_cpu(cpu); /* Note the use of the double underscored version of the API */ __register_cpu_notifier(&foobar_cpu_notifier); cpu_notifier_register_done(); Fix the code in net/core/flow.c by using this latter form of callback registration. Cc: Li RongQing Cc: Sasha Levin Cc: Andrew Morton Cc: Chris Metcalf Cc: Ingo Molnar Cc: netdev@vger.kernel.org Signed-off-by: David S. Miller Signed-off-by: Srivatsa S. Bhat Git-commit: e30a293e8ad7e6048d6d88bcc114094f964bd67b Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git [osvaldob@codeaurora.org: remove use of {get,put}_online_cpus()] Signed-off-by: Osvaldo Banuelos --- net/core/flow.c | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-) diff --git a/net/core/flow.c b/net/core/flow.c index d3137ddc1d2f..f74230f80867 100644 --- a/net/core/flow.c +++ b/net/core/flow.c @@ -456,7 +456,8 @@ static int __init flow_cache_init(struct flow_cache *fc) if (!fc->percpu) return -ENOMEM; - get_online_cpus(); + cpu_notifier_register_begin(); + for_each_online_cpu(i) { if (flow_cache_cpu_prepare(fc, i)) goto err; @@ -464,8 +465,9 @@ static int __init flow_cache_init(struct flow_cache *fc) fc->hotcpu_notifier = (struct notifier_block){ .notifier_call = flow_cache_cpu, }; - register_hotcpu_notifier(&fc->hotcpu_notifier); - put_online_cpus(); + __register_hotcpu_notifier(&fc->hotcpu_notifier); + + cpu_notifier_register_done(); setup_timer(&fc->rnd_timer, flow_cache_new_hashrnd, (unsigned long) fc); @@ -475,13 +477,14 @@ static int __init flow_cache_init(struct flow_cache *fc) return 0; err: - put_online_cpus(); for_each_possible_cpu(i) { struct flow_cache_percpu *fcp = per_cpu_ptr(fc->percpu, i); kfree(fcp->hash_table); fcp->hash_table = NULL; } + cpu_notifier_register_done(); + free_percpu(fc->percpu); fc->percpu = NULL;