Messages in this thread | ![/](/images/icornerl.gif) | | Subject | Re: Kernel rwlock design, Multicore and IGMP | From | Eric Dumazet <> | Date | Thu, 11 Nov 2010 16:32:22 +0100 |
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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); }
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