Messages in this thread |  | | | Date | Wed, 28 Jun 2006 01:45:44 -0700 | | From | Andrew Morton <> | | Subject | Re: [Patch] jbd commit code deadloop when installing Linux |
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On 28 Jun 2006 14:50:29 +0800 Zou Nan hai <nanhai.zou@intel.com> wrote:
> On Wed, 2006-06-28 at 16:04, Andrew Morton wrote: > > On 28 Jun 2006 14:02:57 +0800 > > Zou Nan hai <nanhai.zou@intel.com> wrote: > > > > > > > However I think cond_resched_lock and cond_resched_softirq also need fix > > > > > to make the semantic consistent. > > > > > > > > > > Please check the following patch. > > > > > > > > > > > > > Ah. I think the return value from these functions should mean "something > > > > disruptive happened", if you like. > > > > > > > > See, the callers of cond_resched_lock() aren't interested in whether > > > > cond_resched_lock() actually called schedule(). They want to know whether > > > > cond_resched_lock() dropped the lock. Because if the lock was dropped, the > > > > caller needs to take some special action, regardless of whether schedule() > > > > was finally called. > > > > > > > > So I think the patch I queued is OK, agree? > > > > > > I am afraid the code like cond_resched_lock check in > > > fs/jbd/checkpoint.c log_do_checkpoint may fall into endless retry in > > > some condition, will it? > > > > Oh crap, yes. If need_resched() and system_state==SYSTEM_BOOTING then > > cond_resched_lock() will drop the lock but won't schedule. So it'll return > > true but won't clear need_resched() and the caller will lock up. > > > > So if cond_resched_foo() ends up dropping the lock it _must_ call > > schedule() to clear need_resched(). > > > > So, how about this (it needs some code comments!) > > > > > > The patch works for the install test env.
Thanks.
> However I still have some concern on cond_resched_lock(), on an UP > kernel it will return 1 if schedule happen, but actually it does not > drop any lock, that semantic seems to be different to SMP kernel.
That's OK (I think - I don't have a good track record in this thread).
If the kernel is non-preemptible and UP, we want to return true from cond_resched_foo() if we called schedule(). Because schedule() might allow a different thread into the kernel which might modify the locked data.
And if the kernel is preemptible and UP, we want to return true from cond_resched_foo() if we dropped the lock, because that internally does a preempt_enable().
And the patch (hopefully) satisfies those requirements. Does that all sound solid?
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