Messages in this thread Patch in this message | | | Subject | Re: [PATCH] clk: fix spin_lock/unlock imbalance on bad clk_enable() reentrancy | From | David Lechner <> | Date | Fri, 22 Dec 2017 12:42:50 -0600 |
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On 12/21/2017 07:39 PM, Stephen Boyd wrote: > On 12/20, Stephen Boyd wrote: >> On 12/20, David Lechner wrote: >>> On 12/20/2017 02:33 PM, David Lechner wrote: >>> >>> >>> So, the question I have is: what is the actual "correct" behavior of >>> spin_trylock_irqsave()? Is it really supposed to always return true >>> when CONFIG_DEBUG_SPINLOCK=n and CONFIG_SMP=n or is this a bug? >> >> Thanks for doing the analysis in this thread. >> >> When CONFIG_DEBUG_SPINLOCK=n and CONFIG_SMP=n, spinlocks are >> compiler barriers, that's it. So even if it is a bug to always >> return true, I fail to see how we can detect that a spinlock is >> already held in this configuration and return true or false. >> >> I suppose the best option is to make clk_enable_lock() and >> clk_enable_unlock() into nops or pure owner/refcount/barrier >> updates when CONFIG_SMP=n. We pretty much just need the barrier >> semantics when there's only a single CPU. >> > > How about this patch? It should make the trylock go away on UP > configs and then we keep everything else for refcount and > ownership. We would test enable_owner outside of any > irqs/preemption disabled section though. That needs a think. > > ---8<---- > diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c > index 3526bc068f30..b6f61367aa8d 100644 > --- a/drivers/clk/clk.c > +++ b/drivers/clk/clk.c > @@ -143,7 +143,8 @@ static unsigned long clk_enable_lock(void) > { > unsigned long flags; > > - if (!spin_trylock_irqsave(&enable_lock, flags)) { > + if (!IS_ENABLED(CONFIG_SMP) || > + !spin_trylock_irqsave(&enable_lock, flags)) { > if (enable_owner == current) { > enable_refcnt++; > __acquire(enable_lock); > >
After sleeping on it, this is what I came up with. This keeps enable_owner and enable_refcnt protected and basically does the same thing that spin_lock_irqsave()/spin_unlock_irqrestore() would do on a UP system anyway, just more explicitly.
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diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c index bb1b1f9..adbace3 100644 --- a/drivers/clk/clk.c +++ b/drivers/clk/clk.c @@ -136,6 +136,8 @@ static void clk_prepare_unlock(void) mutex_unlock(&prepare_lock); }
+#ifdef CONFIG_SMP + static unsigned long clk_enable_lock(void) __acquires(enable_lock) { @@ -170,6 +172,43 @@ static void clk_enable_unlock(unsigned long flags) spin_unlock_irqrestore(&enable_lock, flags); }
+#else + +static unsigned long clk_enable_lock(void) + __acquires(enable_lock) +{ + unsigned long flags; + + __acquire(enable_lock); + local_irq_save(flags); + preempt_disable(); + + if (enable_refcnt++ == 0) { + WARN_ON_ONCE(enable_owner != NULL); + enable_owner = current; + } else { + WARN_ON_ONCE(enable_owner != current); + } + + return flags; +} + +static void clk_enable_unlock(unsigned long flags) + __releases(enable_lock) +{ + WARN_ON_ONCE(enable_owner != current); + WARN_ON_ONCE(enable_refcnt == 0); + + if (--enable_refcnt == 0) + enable_owner = NULL; + + __release(enable_lock); + local_irq_restore(flags); + preempt_enable(); +} + +#endif + static bool clk_core_is_prepared(struct clk_core *core) { bool ret = false;
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