[PATCH] OMAP: clock: fix race in disable all clocks

[Paul Walmsley]

Hi

adding Todd to cc

On Thu, 15 Mar 2012, Nishanth Menon wrote:

> clk_disable_unused is invoked when CONFIG_OMAP_RESET_CLOCKS=y.
> Since clk_disable_unused is called as lateinitcall, there can
> be more than a few workqueues executing off secondary CPU(s).
> The current code does the following:
> a) checks if clk is unused
> b) holds lock
> c) disables clk
> d) unlocks
> 
> Between (a) and (b) being executed on CPU0, It is possible to
> have a driver executing on CPU1 which could do a get_sync->clk_get
> (and increase the use_count) of the clock which was just about
> to be disabled by clk_disable_unused.
> 
> We ensure instead that the entire list traversal is protected by
> the lock allowing for parent child clock traversal which could be
> potentially be done by runtime operations to be safe as well.
> 
> Reported-by: Todd Poynor <toddpoynor at google.com>
> Signed-off-by: Nishanth Menon <nm at ti.com>

Thanks, I'll queue this for v3.4-rc1.

In the medium term, we should get rid of CONFIG_OMAP_RESET_CLOCKS, at 
least for the OMAP2+ chips, and just do this by default.  But this will 
need to wait until all of the OMAP2+ devices and drivers have been 
converted to use hwmod.  Patches to that end are also gladly accepted :-)
In 3.5 we should be in pretty good shape for OMAP4, but OMAP2/3 will still 
need some work.



- Paul