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Date: Thu, 13 Jun 2019 22:07:44 +0800 From: Xiaoming Ni <nixiaoming@...wei.com> To: <vvs@...tuozzo.com>, <adobriyan@...ru>, <adobriyan@...il.com>, <akpm@...ux-foundation.org>, <tglx@...utronix.de>, <gregkh@...uxfoundation.org>, <mingo@...nel.org>, <viresh.kumar@...aro.org>, <luto@...nel.org>, <arjan@...ux.intel.com>, <Nadia.Derbey@...l.net> CC: <linux-kernel@...r.kernel.org>, <torvalds@...ux-foundation.org>, <stern@...land.harvard.edu>, <paulmck@...ux.vnet.ibm.com>, <masami.hiramatsu.pt@...achi.com>, <alex.huangjianhui@...wei.com>, <dylix.dailei@...wei.com> Subject: [PATCH] kernel/notifier.c: remove notifier_chain_register Registering the same notifier to a hook repeatedly can cause the hook list to form a ring or lose other members of the list. case1: An infinite loop in notifier_chain_register can cause soft lockup atomic_notifier_chain_register(&test_notifier_list, &test_notifier1); atomic_notifier_chain_register(&test_notifier_list, &test_notifier1); atomic_notifier_chain_register(&test_notifier_list, &test_notifier2); case2: An infinite loop in notifier_chain_register can cause soft lockup atomic_notifier_chain_register(&test_notifier_list, &test_notifier1); atomic_notifier_chain_register(&test_notifier_list, &test_notifier1); atomic_notifier_call_chain(&test_notifier_list, 0, NULL); case3: lose other hook "test_notifier2" atomic_notifier_chain_register(&test_notifier_list, &test_notifier1); atomic_notifier_chain_register(&test_notifier_list, &test_notifier2); atomic_notifier_chain_register(&test_notifier_list, &test_notifier1); case4: Unregister returns 0, but the hook is still in the linked list, and it is not really registered. If you call notifier_call_chain after ko is unloaded, it will trigger oops. If the system is configured with softlockup_panic and the same hook is repeatedly registered on the panic_notifier_list, it will cause a loop panic. The only difference between notifier_chain_cond_register and notifier_chain_register is that a check is added in order to avoid registering the same notifier multiple times to the same hook. So consider removing notifier_chain_register and replacing it with notifier_chain_cond_register. Signed-off-by: Xiaoming Ni <nixiaoming@...wei.com> --- kernel/notifier.c | 26 ++++++-------------------- 1 file changed, 6 insertions(+), 20 deletions(-) diff --git a/kernel/notifier.c b/kernel/notifier.c index d9f5081..56efd54 100644 --- a/kernel/notifier.c +++ b/kernel/notifier.c @@ -19,20 +19,6 @@ * are layered on top of these, with appropriate locking added. */ -static int notifier_chain_register(struct notifier_block **nl, - struct notifier_block *n) -{ - while ((*nl) != NULL) { - WARN_ONCE(((*nl) == n), "double register detected"); - if (n->priority > (*nl)->priority) - break; - nl = &((*nl)->next); - } - n->next = *nl; - rcu_assign_pointer(*nl, n); - return 0; -} - static int notifier_chain_cond_register(struct notifier_block **nl, struct notifier_block *n) { @@ -127,7 +113,7 @@ int atomic_notifier_chain_register(struct atomic_notifier_head *nh, int ret; spin_lock_irqsave(&nh->lock, flags); - ret = notifier_chain_register(&nh->head, n); + ret = notifier_chain_cond_register(&nh->head, n); spin_unlock_irqrestore(&nh->lock, flags); return ret; } @@ -223,10 +209,10 @@ int blocking_notifier_chain_register(struct blocking_notifier_head *nh, * such times we must not call down_write(). */ if (unlikely(system_state == SYSTEM_BOOTING)) - return notifier_chain_register(&nh->head, n); + return notifier_chain_cond_register(&nh->head, n); down_write(&nh->rwsem); - ret = notifier_chain_register(&nh->head, n); + ret = notifier_chain_cond_register(&nh->head, n); up_write(&nh->rwsem); return ret; } @@ -349,7 +335,7 @@ int blocking_notifier_call_chain(struct blocking_notifier_head *nh, int raw_notifier_chain_register(struct raw_notifier_head *nh, struct notifier_block *n) { - return notifier_chain_register(&nh->head, n); + return notifier_chain_cond_register(&nh->head, n); } EXPORT_SYMBOL_GPL(raw_notifier_chain_register); @@ -431,10 +417,10 @@ int srcu_notifier_chain_register(struct srcu_notifier_head *nh, * such times we must not call mutex_lock(). */ if (unlikely(system_state == SYSTEM_BOOTING)) - return notifier_chain_register(&nh->head, n); + return notifier_chain_cond_register(&nh->head, n); mutex_lock(&nh->mutex); - ret = notifier_chain_register(&nh->head, n); + ret = notifier_chain_cond_register(&nh->head, n); mutex_unlock(&nh->mutex); return ret; } -- 1.8.5.6
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