On 05/15/2012 12:42 PM, Sascha Hauer wrote:
Hi Saravana,
On Fri, May 11, 2012 at 09:59:56PM -0700, Saravana Kannan wrote:
Without this patch, the following race conditions are possible.
Race condition 1:
* clk-A has two parents - clk-X and clk-Y.
* All three are disabled and clk-X is current parent.
* Thread A: clk_set_parent(clk-A, clk-Y).
* Thread A:<snip execution flow>
* Thread A: Grabs enable lock.
* Thread A: Sees enable count of clk-A is 0, so doesn't enable clk-Y.
* Thread A: Releases enable lock.
* Thread B: Calls clk_enable(clk-A), which in turn enables clk-X.
* Thread A: Switches clk-A's parent to clk-Y in hardware.
clk-A is now enabled in software, but not clocking in hardware.
Race condition 2:
* clk-A has two parents - clk-X and clk-Y.
* All three are disabled and clk-X is current parent.
* Thread A: clk_set_parent(clk-A, clk-Y).
* Thread A:<snip execution flow>
* Thread A: Switches parent in hardware to clk-Y.
* Thread A: Grabs enable lock.
* Thread A: Sees enable count of clk-A is 0, so doesn't disable clk-X.
* Thread A: Releases enable lock.
* Thread B: Calls clk_enable(clk-A)
* Thread B: Software state still says parent is clk-X.
* Thread B: So, enables clk-X and then itself.
* Thread A: Updates parent in software state to clk-Y.
Had a look at this and I can follow your reasoning and you patch seems
to fix this. However, there is a problem,
/* migrate prepare and enable */
@@ -1092,23 +1098,23 @@ static int __clk_set_parent(struct clk *clk, struct clk *parent)
/* FIXME replace with clk_is_enabled(clk) someday */
spin_lock_irqsave(&enable_lock, flags);
+
if (clk->enable_count)
__clk_enable(parent);
- spin_unlock_irqrestore(&enable_lock, flags);
/* change clock input source */
ret = clk->ops->set_parent(clk->hw, i);
You call ->set_parent while holding a spinlock. This won't work with i2c
clocks.
I did account for that. I explained it in the commit text. Please let me
know if any part of that is not clear or is not correct.
Thanks,
Saravana
--
Sent by an employee of the Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.
--
To unsubscribe from this list: send the line "unsubscribe linux-arm-msm" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
