Messages in this thread Patch in this message | | | Subject | Re: [PATCH] Fix a race in pid generation that causes pids to be reused immediately. | From | Eric Dumazet <> | Date | Tue, 15 Jun 2010 06:38:46 +0200 |
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Le lundi 14 juin 2010 à 21:21 -0700, Andrew Morton a écrit : > On Tue, 15 Jun 2010 13:26:08 +1000 Paul Mackerras <paulus@samba.org> wrote: > > > On Mon, Jun 14, 2010 at 06:55:56PM -0700, Andrew Morton wrote: > > > > > > kernel/sched_clock.c: if (cmpxchg64(&scd->clock, old_clock, clock) != old_cloc > > > > > > I guess that'll flush out any stragglers. > > > > And break most non-x86 32-bit architectures, including 32-bit powerpc. > > If CONFIG_SMP=y, yes. On UP there's a generic implementation > (include/asm-generic/cmpxchg-local.h, include/asm-generic/cmpxchg.h) > > > Fortunately that code is only used if CONFIG_HAVE_UNSTABLE_SCHED_CLOCK > > is set, and it looks like only x86 and ia64 set it. > > > > If that happens then the best fix is for those architectures to get > themselves a cmpxchg64(). Unless for some reason it's simply > unimplementable? Worst case I guess one could use a global spinlock. > Second-worst-case: hashed spinlocks.
Hmm, this reminds me a patch I had somewhere, not yet sent to David :)
1) cmpxchg() was not available for all arches, maybe atomic_long_cmpxchg() is ?
2) I am not sure atomic_long_t quarantee that all 32 or 64 bits of the underlying long container are available.
Thanks !
diff --git a/net/ipv4/route.c b/net/ipv4/route.c index a291edb..335ca89 100644 --- a/net/ipv4/route.c +++ b/net/ipv4/route.c @@ -1268,17 +1268,18 @@ skip_hashing: void rt_bind_peer(struct rtable *rt, int create) { - static DEFINE_SPINLOCK(rt_peer_lock); struct inet_peer *peer; peer = inet_getpeer(rt->rt_dst, create); - spin_lock_bh(&rt_peer_lock); - if (rt->peer == NULL) { - rt->peer = peer; +#if defined(__HAVE_ARCH_CMPXCHG) + if (!cmpxchg(&rt->peer, NULL, peer)) peer = NULL; - } - spin_unlock_bh(&rt_peer_lock); +#else + BUILD_BUG_ON(sizeof(rt->peer) != sizeof(atomic_long_t)); + if (!atomic_long_cmpxchg((atomic_long_t *)&rt->peer, 0, (long)peer)) + peer = NULL; +#endif if (peer) inet_putpeer(peer); }
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