From: Oleg Nesterov <oleg@redhat.com>
To: Tomas Henzl <thenzl@redhat.com>
Cc: Jack Wang <xjtuwjp@gmail.com>,
Jason Seba <jason.seba42@gmail.com>,
Suresh Thiagarajan <Suresh.Thiagarajan@pmcs.com>,
Viswas G <Viswas.G@pmcs.com>,
"linux-scsi@vger.kernel.org" <linux-scsi@vger.kernel.org>,
"JBottomley@parallels.com" <JBottomley@parallels.com>,
Vasanthalakshmi Tharmarajan
<Vasanthalakshmi.Tharmarajan@pmcs.com>
Subject: Re: [PATCH] pm80xx: Spinlock fix
Date: Mon, 23 Dec 2013 16:38:51 +0100 [thread overview]
Message-ID: <20131223153851.GA27812@redhat.com> (raw)
In-Reply-To: <52B8569D.4050101@redhat.com>
On 12/23, Tomas Henzl wrote:
>
> On 12/23/2013 04:06 PM, Jack Wang wrote:
> > On 12/23/2013 03:55 PM, Jason Seba wrote:
> >> Why is this considered dangerous? I put some thought into it and
> >> couldn't find any obvious reason why it wouldn't work, but I also
> >> couldn't find any other drivers that work this way. Is there a
> >> particular reason to avoid doing it this way?
> >>
> > If you use global flags, you may change interrupt state depends on context.
>
> The problem could show up when different threads try to store different content to the flags.
Agreed. I have no idea if the patch is right or not, but at least
the changelog should clearly explain that only one thread can do
spin_lock_irqsave(&x->lock, x->lock_flags) at any time, otherwise
the patch (and the code) _looks_ wrong even if it is correct.
And if we can't use a local "unsigned long flags" because _unlock
can happen in another function, imho this should be mentioned in
the changelog as well.
Oleg.
prev parent reply other threads:[~2013-12-23 15:38 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-12-18 11:28 [PATCH] pm80xx: Spinlock fix Viswas G
2013-12-23 13:07 ` Tomas Henzl
2013-12-23 13:32 ` Jack Wang
2013-12-23 13:45 ` Suresh Thiagarajan
2013-12-23 14:55 ` Jason Seba
2013-12-23 15:06 ` Jack Wang
2013-12-23 15:28 ` Tomas Henzl
2013-12-23 15:33 ` Jason Seba
2013-12-23 15:36 ` Tomas Henzl
2013-12-23 16:34 ` Oleg Nesterov
2013-12-23 17:27 ` spinlock_irqsave() && flags (Was: pm80xx: Spinlock fix) Oleg Nesterov
2013-12-23 18:12 ` Linus Torvalds
2013-12-23 18:24 ` Oleg Nesterov
2013-12-23 18:43 ` Linus Torvalds
2013-12-23 18:23 ` Ingo Molnar
2013-12-23 18:33 ` Oleg Nesterov
2013-12-24 8:29 ` Ingo Molnar
2013-12-24 9:13 ` Suresh Thiagarajan
2013-12-24 17:29 ` James Bottomley
2013-12-27 16:18 ` Oleg Nesterov
2014-01-02 10:31 ` Suresh Thiagarajan
2014-01-03 20:02 ` Dan Williams
2013-12-23 15:38 ` Oleg Nesterov [this message]
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