Messages in this thread | | | Date | Mon, 19 Jun 2006 10:12:52 +0200 | From | Ingo Molnar <> | Subject | Re: [patch] increase spinlock-debug looping timeouts from 1 sec to 1 min |
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* Andrew Morton <akpm@osdl.org> wrote:
> On Mon, 19 Jun 2006 09:02:29 +0200 > Ingo Molnar <mingo@elte.hu> wrote: > > > Subject: increase spinlock-debug looping timeouts from 1 sec to 1 > > min > > But it's broken. In the non-debug case we subtract RW_LOCK_BIAS so we > know that the writer will get the lock when all readers vacate. But > in the CONFIG_DEBUG_SPINLOCK case we don't do that, with the result > that taking a write_lock can take over a second. > > A much, much better fix (which involves visiting all architectures) > would be to subtract RW_LOCK_BIAS and _then_ wait for a second.
no. Write-locks are unfair too, and there's no guarantee that writes are listened to. That's why nested read_lock() is valid, while nested down_read() is invalid.
Take a look at arch/i386/kernel/semaphore.c, __write_lock_failed() just adds back the RW_LOCK_BIAS and retries in a loop. There's no difference to an open-coded write_trylock loop - unless i'm missing something fundamental.
> OK, it's only debug code. But RH (for one) have decided to ship > zillions of kernels with this debug code turned on.
yes - Fedora enables most of the transparent kernel debugging options (slab, lock debugging) in rawhide. The current list is:
CONFIG_DEBUG_KERNEL=y CONFIG_DEBUG_SLAB=y CONFIG_DEBUG_SLAB_LEAK=y CONFIG_DEBUG_MUTEXES=y CONFIG_DEBUG_SPINLOCK=y CONFIG_DEBUG_SPINLOCK_SLEEP=y CONFIG_DEBUG_HIGHMEM=y CONFIG_DEBUG_BUGVERBOSE=y CONFIG_DEBUG_INFO=y CONFIG_DEBUG_FS=y CONFIG_DEBUG_VM=y CONFIG_DEBUG_STACKOVERFLOW=y CONFIG_DEBUG_STACK_USAGE=y CONFIG_DEBUG_RODATA=y CONFIG_KEYS_DEBUG_PROC_KEYS=y
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