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Date: Sun, 18 Feb 2007 22:27:19 -0800
From: Ben Greear <greearb@...delatech.com>
To: Jarek Poplawski <jarkao2@...pl>
CC: Stephen Hemminger <shemminger@...ux-foundation.org>,
Francois Romieu <romieu@...zoreil.com>, netdev@...r.kernel.org,
Kyle Lucke <klucke@...ibm.com>,
Raghavendra Koushik <raghavendra.koushik@...erion.com>,
Al Viro <viro@....linux.org.uk>
Subject: Re: [PATCH 1/2] RTNL and flush_scheduled_work deadlocks
Jarek Poplawski wrote:
> On Fri, Feb 16, 2007 at 11:04:02AM -0800, Ben Greear wrote:
>
>> Stephen Hemminger wrote:
>>
>>> On Thu, 15 Feb 2007 23:40:32 -0800
>>> Ben Greear <greearb@...delatech.com> wrote:
>>>
>>>> Maybe there should be something like an ASSERT_NOT_RTNL() in the
>>>> flush_scheduled_work()
>>>> method? If it's performance criticial, #ifdef it out if we're not
>>>> debugging locks?
>>>>
>>>>
>>> You can't safely add a check like that. What if another cpu had acquired
>>> RTNL and was unrelated.
>>>
>> I guess there isn't a way to see if *this* thread is the owner of the RTNL
>> currently? I think lockdep knows the owner...maybe could query it somehow,
>> or just save the owner in the mutex object when debugging is enabled...
>>
>
> Here is my patch proposal to enable such thing
> (and to make ASSERT_RTNL simpler btw.).
>
For performance reasons, I'd leave the rtnl_owner inside the
#if debugging locking code....
You are also changing the semantics of ASSERT_RTNL (assert *this thread*
has rtnl, from the
old behaviour: assert *some thread* has rtnl). It may be better this
way, but it could break code that assumes the old behaviour.
Ben
> Signed-off-by: Jarek Poplawski <jarkao2@...pl>
>
> ---
>
> include/linux/rtnetlink.h | 13 +++++++++++--
> net/core/rtnetlink.c | 29 ++++++++++++++++++++++++++---
> 2 files changed, 37 insertions(+), 5 deletions(-)
>
>
> diff -Nurp linux-2.6.20-git13-/include/linux/rtnetlink.h linux-2.6.20-git13/include/linux/rtnetlink.h
> --- linux-2.6.20-git13-/include/linux/rtnetlink.h 2007-02-04 19:44:54.000000000 +0100
> +++ linux-2.6.20-git13/include/linux/rtnetlink.h 2007-02-18 22:56:36.000000000 +0100
> @@ -704,16 +704,25 @@ extern int rtnl_trylock(void);
>
> extern void rtnetlink_init(void);
> extern void __rtnl_unlock(void);
> +extern int rtnl_assert(void);
>
> #define ASSERT_RTNL() do { \
> - if (unlikely(rtnl_trylock())) { \
> - rtnl_unlock(); \
> + if (unlikely(!rtnl_assert())) { \
> printk(KERN_ERR "RTNL: assertion failed at %s (%d)\n", \
> __FILE__, __LINE__); \
> dump_stack(); \
> } \
> } while(0)
>
> +/* Current process shouldn't hold RTNL lock: */
> +#define ASSERT_NOT_RTNL() do { \
> + if (unlikely(rtnl_assert())) { \
> + printk(KERN_ERR "NOT_RTNL: assertion failed at %s (%d)\n", \
> + __FILE__, __LINE__); \
> + dump_stack(); \
> + } \
> +} while(0)
> +
> #define BUG_TRAP(x) do { \
> if (unlikely(!(x))) { \
> printk(KERN_ERR "KERNEL: assertion (%s) failed at %s (%d)\n", \
> diff -Nurp linux-2.6.20-git13-/net/core/rtnetlink.c linux-2.6.20-git13/net/core/rtnetlink.c
> --- linux-2.6.20-git13-/net/core/rtnetlink.c 2007-02-15 20:07:11.000000000 +0100
> +++ linux-2.6.20-git13/net/core/rtnetlink.c 2007-02-18 22:50:13.000000000 +0100
> @@ -57,20 +57,33 @@
> #endif /* CONFIG_NET_WIRELESS_RTNETLINK */
>
> static DEFINE_MUTEX(rtnl_mutex);
> +static struct thread_info *rtnl_owner;
> static struct sock *rtnl;
>
> void rtnl_lock(void)
> {
> +#if !defined(CONFIG_DEBUG_MUTEXES) && !defined(CONFIG_DEBUG_SPINLOCK)
> + WARN_ON(rtnl_owner == current_thread_info());
> +#endif
> mutex_lock(&rtnl_mutex);
> + rtnl_owner = current_thread_info();
> }
>
> void __rtnl_unlock(void)
> {
> +#if !defined(CONFIG_DEBUG_MUTEXES) && !defined(CONFIG_DEBUG_SPINLOCK)
> + WARN_ON(rtnl_owner != current_thread_info());
> +#endif
> + rtnl_owner = NULL;
> mutex_unlock(&rtnl_mutex);
> }
>
> void rtnl_unlock(void)
> {
> +#if !defined(CONFIG_DEBUG_MUTEXES) && !defined(CONFIG_DEBUG_SPINLOCK)
> + WARN_ON(rtnl_owner != current_thread_info());
> +#endif
> + rtnl_owner = NULL;
> mutex_unlock(&rtnl_mutex);
> if (rtnl && rtnl->sk_receive_queue.qlen)
> rtnl->sk_data_ready(rtnl, 0);
> @@ -79,7 +92,16 @@ void rtnl_unlock(void)
>
> int rtnl_trylock(void)
> {
> - return mutex_trylock(&rtnl_mutex);
> + int ret;
> +
> + if ((ret = mutex_trylock(&rtnl_mutex)))
> + rtnl_owner = current_thread_info();
> + return ret;
> +}
> +
> +int rtnl_assert(void)
> +{
> + return (rtnl_owner == current_thread_info());
> }
>
> int rtattr_parse(struct rtattr *tb[], int maxattr, struct rtattr *rta, int len)
> @@ -805,9 +827,9 @@ static void rtnetlink_rcv(struct sock *s
> unsigned int qlen = 0;
>
> do {
> - mutex_lock(&rtnl_mutex);
> + rtnl_lock();
> netlink_run_queue(sk, &qlen, &rtnetlink_rcv_msg);
> - mutex_unlock(&rtnl_mutex);
> + __rtnl_unlock();
>
> netdev_run_todo();
> } while (qlen);
> @@ -893,3 +915,4 @@ EXPORT_SYMBOL(rtnl_unlock);
> EXPORT_SYMBOL(rtnl_unicast);
> EXPORT_SYMBOL(rtnl_notify);
> EXPORT_SYMBOL(rtnl_set_sk_err);
> +EXPORT_SYMBOL(rtnl_assert);
> -
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>
--
Ben Greear <greearb@...delatech.com>
Candela Technologies Inc http://www.candelatech.com
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