Messages in this thread Patch in this message | | | Date | Mon, 6 Feb 2006 22:36:18 +0100 | From | Ingo Molnar <> | Subject | Re: [PATCH] Prevent spinlock debug from timing out too early |
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* Andi Kleen <ak@suse.de> wrote:
> Index: linux-2.6.15/lib/spinlock_debug.c > =================================================================== > --- linux-2.6.15.orig/lib/spinlock_debug.c > +++ linux-2.6.15/lib/spinlock_debug.c > @@ -68,13 +68,13 @@ static inline void debug_spin_unlock(spi > static void __spin_lock_debug(spinlock_t *lock) > { > int print_once = 1; > - u64 i; > > for (;;) { > - for (i = 0; i < loops_per_jiffy * HZ; i++) { > - cpu_relax(); > + unsigned long timeout = jiffies + HZ; > + while (time_before(jiffies, timeout)) { > if (__raw_spin_trylock(&lock->raw_lock)) > return; > + cpu_relax();
The reason i added a loop counter was to solve the case where we are spinning with interrupts disabled - jiffies wont increase there! But i agree that loops_per_jiffy is the wrong metric to use.
a better solution would be to call __delay(1) after the first failed attempt, that would make the delay at least 1 second long. It seems __delay() is de-facto exported by every architecture, so we can rely on it in the global spinlock code.
So how about the patch below instead?
[detail: i moved the __delay() after the second attempted trylock, this way we'll have 2 trylocks without a delay - for ultra-short critical sections.]
Ingo
---- fix spinlock debugging delays to not time out too early. Bug found by Andi Kleen.
Signed-off-by: Ingo Molnar <mingo@elte.hu>
--- linux/lib/spinlock_debug.c.orig +++ linux/lib/spinlock_debug.c @@ -72,9 +72,9 @@ static void __spin_lock_debug(spinlock_t for (;;) { for (i = 0; i < loops_per_jiffy * HZ; i++) { - cpu_relax(); if (__raw_spin_trylock(&lock->raw_lock)) return; + __delay(1); } /* lockup suspected: */ if (print_once) { @@ -144,9 +144,9 @@ static void __read_lock_debug(rwlock_t * for (;;) { for (i = 0; i < loops_per_jiffy * HZ; i++) { - cpu_relax(); if (__raw_read_trylock(&lock->raw_lock)) return; + __delay(1); } /* lockup suspected: */ if (print_once) { @@ -217,9 +217,9 @@ static void __write_lock_debug(rwlock_t for (;;) { for (i = 0; i < loops_per_jiffy * HZ; i++) { - cpu_relax(); if (__raw_write_trylock(&lock->raw_lock)) return; + __delay(1); } /* lockup suspected: */ if (print_once) { - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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