From: Oleg Nesterov <oleg@redhat.com>
To: Jason Seba <jason.seba42@gmail.com>
Cc: Tomas Henzl <thenzl@redhat.com>, Jack Wang <xjtuwjp@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 17:34:10 +0100 [thread overview]
Message-ID: <20131223163410.GA28220@redhat.com> (raw)
In-Reply-To: <CAD0Z9TK-cn=X3ywSzPnEQN-FB+ue+0dHQ3EHuwonC+KfgrmPMA@mail.gmail.com>
On 12/23, Jason Seba wrote:
>
> Wouldn't the contents of the global flags value be protected by the
> spinlock itself?
This can be even true because nowadays spin_lock_irqsave() writes to
"flags" after it takes the lock, and _irqrestore works gets the copy
of "flags" before it releases the lock.
Still this doesn't look safe and afaik this is not documented. Although
I have to admit that after I actually looked at the current implementation
I think this should work.
Perhaps we should ask the maintainers upstream? Even if this works, I am
not sure this is _supposed_ to work. I mean, in theory spin_lock_irqave()
can be changed as, say
#define spin_lock_irqsave(lock, flags) \
do { \
local_irq_save(flags); \
spin_lock(lock); \
} while (0)
(and iirc it was defined this way a long ago). In this case "flags" is
obviously not protected.
Oleg.
next prev parent reply other threads:[~2013-12-23 16:33 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 [this message]
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 ` [PATCH] pm80xx: Spinlock fix Oleg Nesterov
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