linux-kernel - perf_mmap__write_tail() and control dependencies

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Date:	Fri, 24 Jul 2015 08:29:05 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	peterz@...radead.org
Cc:	will.deacon@....com, linux-kernel@...r.kernel.org,
	linux-arch@...r.kernel.org, paulus@...ba.org, rostedt@...dmis.org
Subject: perf_mmap__write_tail() and control dependencies

Hello, Peter,

The ring-buffer code uses control dependencies, and the shiny new
READ_ONCE_CTRL() is now in mainline.  I was idly curious about whether
the write side could use smp_store_release(), and I found this:

static inline void perf_mmap__write_tail(struct perf_mmap *md, u64 tail)
{
	struct perf_event_mmap_page *pc = md->base;

	/*
	 * ensure all reads are done before we write the tail out.
	 */
	mb();
	pc->data_tail = tail;
}

I see mb() rather than smp_mb().  Did I find the correct code for the
write side?  If so, why mb() rather than smp_mb()?  To serialize against
MMIO interactions with hardware counters or some such?

							Thanx, Paul

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