Messages in this thread | | | From | Heiko Stübner <> | Subject | Re: [PATCH] clk: readd refcounting for struct clk instances [when used in pm_clk_add_clk(), genpd] | Date | Wed, 16 Sep 2015 11:18:05 +0200 |
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Hi Stephen,
Am Dienstag, 15. September 2015, 17:39:31 schrieb Stephen Boyd: > On 09/15, Heiko Stübner wrote: > > 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. > > > > Signed-off-by: Heiko Stuebner <heiko@sntech.de> > > --- > > I stumbled upon this while applying the new Rockchip power-domain driver, > > but I guess the underlying issue is universal and probably present since > > the original clk/clk_core split, so this probably counts as fix. > > Ok. The fix makes sense, but I wonder why we do this. Perhaps we > should stop exporting __clk_get() and __clk_put() to everything > that uses clkdev in the kernel. They're called per-user clks for > a reason. There's one user. Now we have two users of the same > struct clk instance, so we have to refcount it too? I hope the > shared clk instance isn't being used to set rates in two pieces > of code. > > And this only affects pm_clk_add_clk() callers right? So the only > caller in the kernel (drivers/clk/shmobile/clk-mstp.c) doesn't > seem to have this problem right now because it never calls > clk_put() on the pointer it passes to pm_clk_add_clk().
As written above, I stumbled upon this with the new Rockchip power-domain driver [0] which calls pm_clk_add_clk in its rockchip_pd_attach_dev() function
[0] http://www.spinics.net/lists/kernel/msg2070432.html
> So what if we did the patch below? This would rely on callers not > calling clk_put() before calling pm_clk_remove() or > pm_clk_destroy(), and the life cycle would be clear, but the > sharing is still there. Or we could say that after a clk is given > to pm_clk_add_clk() that the caller shouldn't touch it anymore, > like shmobile is doing right now. Then there's nothing to do > besides remove the extra __clk_get() call in the pm layer.
I guess that is the call of the genpd people (Rafael and Pavel according to get_maintainers.pl). I'm very much fine with adapting the Rockchip power- domain driver as needed to new handling paradigms.
Personally I'd prefer your solution of making the initial handler do all the getting and putting, as doing clk_get in the power-domain driver and relying on clk_put being done in the genpd core feels awkward. Although that solution would mean, the calling driver would also need to keep track of clocks, while the current rockchip power-domain driver can just call clk_put after handing the clock of to genpd.
> > > @@ -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)) > > Why did we grow a pair of parenthesis?
Remnant of me moving code around, sorry about that. As it seems you prefer a different solution, I'll refrain from sending a fixed version, till we decide which way to go :-).
> > > + 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 > > diff --git a/drivers/base/power/clock_ops.c b/drivers/base/power/clock_ops.c > index 652b5a367c1f..ef62bb3d7b26 100644 > --- a/drivers/base/power/clock_ops.c > +++ b/drivers/base/power/clock_ops.c > @@ -31,6 +31,7 @@ struct pm_clock_entry { > char *con_id; > struct clk *clk; > enum pce_status status; > + bool needs_clk_put; > }; > > /** > @@ -59,8 +60,10 @@ static inline void __pm_clk_enable(struct device *dev, > struct pm_clock_entry *ce */ > static void pm_clk_acquire(struct device *dev, struct pm_clock_entry *ce) > { > - if (!ce->clk) > + if (!ce->clk) { > ce->clk = clk_get(dev, ce->con_id); > + ce->needs_clk_put = true; > + } > if (IS_ERR(ce->clk)) { > ce->status = PCE_STATUS_ERROR; > } else { > @@ -93,7 +96,7 @@ static int __pm_clk_add(struct device *dev, const char > *con_id, return -ENOMEM; > } > } else { > - if (IS_ERR(clk) || !__clk_get(clk)) { > + if (IS_ERR(clk)) { > kfree(ce); > return -ENOENT; > } > @@ -149,7 +152,8 @@ static void __pm_clk_remove(struct pm_clock_entry *ce) > > if (ce->status >= PCE_STATUS_ACQUIRED) { > clk_unprepare(ce->clk); > - clk_put(ce->clk); > + if (ce->needs_clk_put) > + clk_put(ce->clk); > } > }
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