From: Andrew Morton <akpm@linux-foundation.org>
To: Roland Dreier <rdreier@cisco.com>
Cc: Mike Frysinger <vapier@gentoo.org>,
Luca Barbieri <luca@luca-barbieri.com>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] lib/atomic64_test: do not build on non-atomic64 systems
Date: Sun, 24 Oct 2010 18:52:08 -0700 [thread overview]
Message-ID: <20101024185208.6a7e0648.akpm@linux-foundation.org> (raw)
In-Reply-To: <adavd4ro94d.fsf@cisco.com>
On Sun, 24 Oct 2010 09:20:34 -0700 Roland Dreier <rdreier@cisco.com> wrote:
> > That's only part of the problem. The following won't build also:
>
> > drivers/infiniband/hw
>
> Interesting... I hadn't looked at that usage before. Both drivers that
> seem to use atomic64 already depend on 64BIT in Kconfig, so I suspect
> the intersection of 64BIT and !ATOMIC64 is empty?
>
> But eg drivers/infiniband/hw/qib/qib_rc.c does essentially:
>
> atomic64_t *maddr;
> u64 sdata = <something>
> ...
> maddr = (atomic64_t *) qp->r_sge.sge.vaddr;
> atomic64_add_return(sdata, maddr)
>
> is it legit to cast some random address to atomic64_t and expect it to
> work across archs that implement atomic64?
Not really. If someone implements atomic64 on 32-bit they may
do it by putting a spinlock in the atomic64_t. Or they might use
hashed spinlocks, in which case that'll work.
Probably hashed spinlocks, given the (realtively new) convention that
the all-zeroes pattern is a legit way of initialising an atomic_t.
prev parent reply other threads:[~2010-10-25 1:52 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-10-16 17:27 [PATCH] lib/atomic64_test: do not build on non-atomic64 systems Mike Frysinger
2010-10-21 22:02 ` Andrew Morton
2010-10-21 22:23 ` Mike Frysinger
2010-10-21 22:55 ` Andrew Morton
2010-10-21 23:04 ` Mike Frysinger
2010-10-21 23:24 ` Andrew Morton
2010-10-22 20:14 ` Mike Frysinger
2010-10-22 20:31 ` Andrew Morton
2010-10-22 20:47 ` Mike Frysinger
2010-10-22 21:00 ` Andrew Morton
2010-10-22 21:07 ` Mike Frysinger
2010-10-24 16:20 ` Roland Dreier
2010-10-25 1:52 ` Andrew Morton [this message]
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