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, 15 Dec 2017 10:29:56 -0600 |
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On 12/12/2017 10:14 PM, David Lechner wrote: > On 12/12/2017 05:43 PM, David Lechner wrote: >> If clk_enable() is called in reentrant way and spin_trylock_irqsave() is >> not working as expected, it is possible to get a negative enable_refcnt >> which results in a missed call to spin_unlock_irqrestore(). >> >> It works like this: >> >> 1. clk_enable() is called. >> 2. clk_enable_unlock() calls spin_trylock_irqsave() and sets >> enable_refcnt = 1. >> 3. Another clk_enable() is called before the first has returned >> (reentrant), but somehow spin_trylock_irqsave() is returning true. >> (I'm not sure how/why this is happening yet, but it is happening >> to me >> with arch/arm/mach-davinci clocks that I am working on). > > I think I have figured out that since CONFIG_SMP=n and > CONFIG_DEBUG_SPINLOCK=n on my kernel that > > #define arch_spin_trylock(lock)({ barrier(); (void)(lock); 1; }) > > in include/linux/spinlock_up.h is causing the problem. > > So, basically, reentrancy of clk_enable() is broken for non-SMP systems, > but I'm not sure I know how to fix it. > >
Here is what I came up with for a fix. If it looks reasonable, I will resend as a proper patch.
diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c index bb1b1f9..53fad5f 100644 --- a/drivers/clk/clk.c +++ b/drivers/clk/clk.c @@ -136,12 +136,23 @@ static void clk_prepare_unlock(void) mutex_unlock(&prepare_lock); }
+#ifdef CONFIG_SMP +#define NO_SMP 0 +#else +#define NO_SMP 1 +#endif + static unsigned long clk_enable_lock(void) __acquires(enable_lock) { - unsigned long flags; + unsigned long flags = 0;
- if (!spin_trylock_irqsave(&enable_lock, flags)) { + /* + * spin_trylock_irqsave() always returns true on non-SMP system (unless + * spin lock debugging is enabled) so don't call spin_trylock_irqsave() + * unless we are on an SMP system. + */ + if (NO_SMP || !spin_trylock_irqsave(&enable_lock, flags)) { if (enable_owner == current) { enable_refcnt++; __acquire(enable_lock);
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