Messages in this thread Patch in this message | | | From | Heiko Stübner <> | Subject | [PATCH v2] clk: readd refcounting for struct clk instances | Date | Wed, 23 Sep 2015 01:55:47 +0200 |
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With the split into struct clk and struct clk_core, clocks lost the ability for nested __clk_get clkdev calls. While it stays possible to call __clk_get, the first call to (__)clk_put will clear the struct clk, making subsequent clk_put calls run into a NULL pointer dereference.
One prime example of this sits in the generic power domain code, where it is possible to add the clocks both by name and by passing in a struct clk via pm_clk_add_clk(). __pm_clk_add() in turn then calls __clk_get to increase the refcount, so that the original code can put the clock again.
A possible call-path looks like clk = of_clk_get(); pm_clk_add_clk(dev, clk); clk_put(clk);
with pm_clk_add_clk() => __pm_clk_add() then calling __clk_get on the clk and later clk_put when the pm clock list gets destroyed, thus creating a NULL pointer deref, as the struct clk doesn't exist anymore.
So add a separate refcounting for struct clk instances and only clean up once the refcount reaches zero. This makes it possible again to hand off a clock reference to common code without needing to track it further.
Signed-off-by: Heiko Stuebner <heiko@sntech.de> ---
While it may be nice to do the actual handling of the clock references only in the calling code, in this current use case it would create a big additional overhead.
It looks like this so called synchronous reset on power-domain state- changes, requiring device clocks to be turned on, is not that uncommon or rockchip-specific. For this Kevin requested that we read the clocks from the actual consumer devices and not double-list them in the power-domain node as well.
So when expecting pm_clk_add_clk() to work, the current powerdomain code can simply do when adding a device to a domain in rockchip_pd_attach_dev(): while ((clk = of_clk_get(dev->of_node, i++)) && !IS_ERR(clk)) { dev_dbg(dev, "adding clock '%pC' to list of PM clocks\n", clk); error = pm_clk_add_clk(dev, clk); clk_put(clk); }
The clock gets handed off to the generic pm clock handling and thus clk_put in there.
On the other hand when only the rockchip power-domain code is expected to get and put the clock, we would require a lot of new overhead, as now the code would also need to track which devices got added to what domain and also all clock-references until the device gets detached again. So this would essentially duplicate a big part of what the genpd-code does (per-domain device-list and per-device clock-list).
As this seems to be not uncommon, future powerdomain drivers might need that too and would also need to duplicate that handling.
When allowing multiple __clk_get and __clk_put calls on the other hand, the overhead for the regular case comes down to one atomic_inc, atomic_sub_and_test and the function call to the new separate release function ;-) .
changes in v2: removed double parentheses found by Stephen Boyd
drivers/clk/clk.c | 31 +++++++++++++++++++++---------- 1 file changed, 21 insertions(+), 10 deletions(-)
diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c index 43e2c3a..7aab1a4 100644 --- a/drivers/clk/clk.c +++ b/drivers/clk/clk.c @@ -85,6 +85,7 @@ struct clk { unsigned long min_rate; unsigned long max_rate; struct hlist_node clks_node; + struct kref ref; }; /*** locking ***/ @@ -2590,7 +2591,7 @@ fail_out: EXPORT_SYMBOL_GPL(clk_register); /* Free memory allocated for a clock. */ -static void __clk_release(struct kref *ref) +static void __clk_core_release(struct kref *ref) { struct clk_core *core = container_of(ref, struct clk_core, ref); int i = core->num_parents; @@ -2606,6 +2607,18 @@ static void __clk_release(struct kref *ref) kfree(core); } +static void __clk_release(struct kref *ref) +{ + struct clk *clk = container_of(ref, struct clk, ref); + + hlist_del(&clk->clks_node); + if (clk->min_rate > clk->core->req_rate || + clk->max_rate < clk->core->req_rate) + clk_core_set_rate_nolock(clk->core, clk->core->req_rate); + + kfree(clk); +} + /* * Empty clk_ops for unregistered clocks. These are used temporarily * after clk_unregister() was called on a clock and until last clock @@ -2684,7 +2697,7 @@ void clk_unregister(struct clk *clk) if (clk->core->prepare_count) pr_warn("%s: unregistering prepared clock: %s\n", __func__, clk->core->name); - kref_put(&clk->core->ref, __clk_release); + kref_put(&clk->core->ref, __clk_core_release); clk_prepare_unlock(); } @@ -2759,12 +2772,14 @@ int __clk_get(struct clk *clk) return 0; kref_get(&core->ref); + kref_get(&clk->ref); } return 1; } void __clk_put(struct clk *clk) { + struct clk_core *core; struct module *owner; if (!clk || WARN_ON_ONCE(IS_ERR(clk))) @@ -2772,19 +2787,15 @@ void __clk_put(struct clk *clk) clk_prepare_lock(); - hlist_del(&clk->clks_node); - if (clk->min_rate > clk->core->req_rate || - clk->max_rate < clk->core->req_rate) - clk_core_set_rate_nolock(clk->core, clk->core->req_rate); + core = clk->core; + owner = core->owner; - owner = clk->core->owner; - kref_put(&clk->core->ref, __clk_release); + kref_put(&clk->ref, __clk_release); + kref_put(&core->ref, __clk_core_release); clk_prepare_unlock(); module_put(owner); - - kfree(clk); } /*** clk rate change notifiers ***/ -- 2.5.1
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