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  PHC 
Open Source and information security mailing list archives
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Date:	Fri, 21 Mar 2014 11:05:59 +0000
From:	Catalin Marinas <>
To:	Viresh Kumar <>
Cc:	"Srivatsa S. Bhat" <>,
	"Rafael J. Wysocki" <>,
	Lists linaro-kernel <>,
	"" <>,
	"" <>,
	Linux Kernel Mailing List <>,
	"" <>
Subject: Re: [PATCH V4 1/3] cpufreq: Make sure frequency transitions are

On Fri, Mar 21, 2014 at 09:21:02AM +0000, Viresh Kumar wrote:
> @Catalin: We have a problem here and need your expert advice. After changing
> CPU frequency we need to call this code:
> cpufreq_notify_post_transition();
> policy->transition_ongoing = false;
> And the sequence must be like this only. Is this guaranteed without any
> memory barriers? cpufreq_notify_post_transition() isn't touching
> transition_ongoing at all..

The above sequence doesn't say much. As rmk said, the compiler wouldn't
reorder the transition_ongoing write before the function call. I think
most architectures (not sure about Alpha) don't do speculative stores,
so hardware wouldn't reorder them either. However, other stores inside
the cpufreq_notify_post_transition() could be reordered after
transition_ongoing store. The same for memory accesses after the
transition_ongoing update, they could be reordered before.

So what we actually need to know is what are the other relevant memory
accesses that require strict ordering with transition_ongoing.

What I find strange in your patch is that
cpufreq_freq_transition_begin() uses spinlocks around transition_ongoing
update but cpufreq_freq_transition_end() doesn't.

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to
More majordomo info at
Please read the FAQ at

Powered by blists - more mailing lists