linux-kernel - Re: [PATCH 4/4] Staging: lustre: sparse lock warning fix

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Message-ID: <20150521081534.GA13975@debian>
Date:	Thu, 21 May 2015 10:15:34 +0200
From:	AdrianRemonda <adrianremonda@...il.com>
To:	Dan Carpenter <dan.carpenter@...cle.com>
Cc:	"open list:STAGING SUBSYSTEM" <devel@...verdev.osuosl.org>,
	"moderated list:STAGING - LUSTRE..." <HPDD-discuss@...1.01.org>,
	Andreas Dilger <andreas.dilger@...el.com>,
	Greg Donald <gdonald@...il.com>,
	open list <linux-kernel@...r.kernel.org>,
	Oleg Drokin <oleg.drokin@...el.com>,
	Julia Lawall <Julia.Lawall@...6.fr>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Joe Perches <joe@...ches.com>
Subject: Re: [PATCH 4/4] Staging: lustre: sparse lock warning fix

On Tue, May 19, 2015 at 12:21:15AM +0300, Dan Carpenter wrote:
> On Mon, May 18, 2015 at 08:34:51PM +0200, Adrian Remonda wrote:
> > Fixed sparse warning: context imbalance in 'nrs_resource_put_safe' -
> > 'different lock contexts for basic block' by releasing the lock on each
> > iteration of the for loop.
> > 
> 
> That changelog doesn't sound correct at all.  That's not a correct
> motivation or explanation.
> 
> I reviewed the patch and it's likely going to cause dead locks. The code
> is trying to take the spinlock for the first pointer in the array and
> release it at the end.  Now it takes the first pointer's spinlock a
> bunch of times (dead lock) and releases it once (will not happen because
> we are already dead).
> 
> 

Hello Dan,

thanks for the comments. The code would end up looking as next, I don't
undertand where the deadlock would be.
I know the older code would work, I just changed it to keep the lock
locked the less time as possible.

        for (i = 0; i < NRS_RES_MAX; i++) {
                if (pols[i] == NULL)
                        continue;

                if (nrs == NULL) {
                        nrs = pols[i]->pol_nrs;
                }
                spin_lock(&nrs->nrs_lock);
                nrs_policy_put_locked(pols[i]);
                spin_unlock(&nrs->nrs_lock);
        }

best regards,
Adrian 
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