lkml.org 
[lkml]   [2010]   [Nov]   [11]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: Kernel rwlock design, Multicore and IGMP
From
Date
Le jeudi 11 novembre 2010 à 16:23 +0100, Eric Dumazet a écrit :
> Le jeudi 11 novembre 2010 à 21:49 +0800, Cypher Wu a écrit :
>
> Hi
>
> CC netdev, since you ask questions about network stuff _and_ rwlock
>
>
> > I'm using TILEPro and its rwlock in kernel is a liitle different than
> > other platforms. It have a priority for write lock that when tried it
> > will block the following read lock even if read lock is hold by
> > others. Its code can be read in Linux Kernel 2.6.36 in
> > arch/tile/lib/spinlock_32.c.
>
> This seems a bug to me.
>
> read_lock() can be nested. We used such a schem in the past in iptables
> (it can re-enter itself),
> and we used instead a spinlock(), but with many discussions with lkml
> and Linus himself if I remember well.

I meant, a percpu spinlock, and extra logic to spin_lock() it one time,
even if nested.

static inline void xt_info_rdlock_bh(void)
{
struct xt_info_lock *lock;
local_bh_disable();
lock = &__get_cpu_var(xt_info_locks);
if (likely(!lock->readers++))
spin_lock(&lock->lock);
}
static inline void xt_info_rdunlock_bh(void)
{
struct xt_info_lock *lock = &__get_cpu_var(xt_info_locks);
if (likely(!--lock->readers))
spin_unlock(&lock->lock);
local_bh_enable();
}
The write 'rwlock' side has to lock the percpu spinlock of all possible
cpus.

/*
* The "writer" side needs to get exclusive access to the lock,
* regardless of readers. This must be called with bottom half
* processing (and thus also preemption) disabled.
*/
static inline void xt_info_wrlock(unsigned int cpu)
{
spin_lock(&per_cpu(xt_info_locks, cpu).lock);
}
static inline void xt_info_wrunlock(unsigned int cpu)
{
spin_unlock(&per_cpu(xt_info_locks, cpu).lock);
}


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2010-11-11 16:35    [from the cache]
©2003-2014 Jasper Spaans. Advertise on this site