linux-kernel - RE: [PATCH] [SCSI] bnx2fc: fix build error when !CONFIG

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Date:	Tue, 8 Mar 2011 11:36:53 -0800
From:	"Zou, Yi" <yi.zou@...el.com>
To:	"Love, Robert W" <robert.w.love@...el.com>,
	James Bottomley <James.Bottomley@...e.de>
CC:	Bhanu Gollapudi <bprakash@...adcom.com>,
	Mariusz Kozlowski <mk@....zgora.pl>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	"linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-next@...r.kernel.org" <linux-next@...r.kernel.org>
Subject: RE: [PATCH] [SCSI] bnx2fc: fix build error when !CONFIG_MODULES

> On Mon, 2011-03-07 at 16:18 -0800, James Bottomley wrote:
> > On Mon, 2011-03-07 at 15:54 -0800, Bhanu Gollapudi wrote:
> > > On Mon, 2011-03-07 at 12:16 -0800, Mariusz Kozlowski wrote:
> > > > On Wed, Mar 02, 2011 at 11:10:03PM +0100, Mariusz Kozlowski wrote:
> > > > > drivers/scsi/bnx2fc/bnx2fc_fcoe.c:1815: error: dereferencing
> pointer to incomplete type
> > > > > drivers/scsi/bnx2fc/bnx2fc_fcoe.c:1815: error:
> ‘MODULE_STATE_LIVE’ undeclared (first use in this function)
> > > >
> > > > Hm. Still there in next-20110307. Is this patch wrong or..?
> > > >
> > >
> > > James,
> > >
> > > Here is my ack for this patch.
> >
> > OK, so the patch is actually wrong because adding #ifdefs on modules in
> > files really impedes readability.  The bug is using a direct deref on
> > module state instead of one of the APIs which work in the non-modular
> > case, namely try_module_get(). That means the other two need to come
> out
> > and be reworked (plus all the others in fcoe).
> >
> > Reworked looks like it might be a bigger item than bnx2fc.  If any of
> > those tests is ever relevant, it means we have a race in the
> > fcoe_transport because it shouldn't be calling function pointers on a
> > dying module (unless it wants to trigger an oops).
> >
> > So, why are you trying to do this in the first place?
> >
> First, fcoe.c started with these checks. Here is a comment in fcoe.c at
> the point of one of the checks.
> 
> /*
>  * Make sure the module has been initialized, and is not about to be
>  * removed.  Module paramter sysfs files are writable before the
>  * module_init function is called and after module_exit.
>  */
> 
> I don't know the correct way to fix that race is, but we may be past the
> need to fix it in the LLDs.
> 
> Next, the fcoe transport was added. Since it (libfcoe.ko) is now calling
> what used to be the fcoe.ko sysfs entry points I don't think the problem
> exists in fcoe.c or in bnx2fc_fcoe.c, the problem should be in the fcoe
> transport code, as James suggested.
> 
> The fcoe transport code already has these checks to protect against
> sysfs files being writable before module initialization is complete. It
> uses the ft_mutex to protect the list of transports(LLDs) so when
> 'create' is called it knows that the transport is still there to call
> down to. It holds the ft_mutex until the LLD's 'create' routine returns.
> The transports(LLDs) should be detaching themselves from the fcoe
> transport layer before they exit. fcoe_transport_detach will try to
> acquire the ft_mutex and block until the 'create' call returns and
> releases the ft_mutex. I think this ensures that the transport(LLD) will
> be fine when the fcoe transport calls it.
> 
> My feeling is that these checks are still needed in the fcoe transport,
> but not in the LLDs. If someone can suggest a better way to protect
> against writable sysfs files when the module hasn't finished
> initializing, we should do that instead of the ifdefs.
> 
> Hope this helps,
> 
> //Rob
> 
> FYI: mnc asked about this code and the trylock code in fcoe and libfcoe.
> I have patches in our internal validation to remove the trylock usage,
> but I don't have patches to fix the module state checking.
> 
Yeah, this logic was from original fixing race condition in fcoe.ko, note
that we do need check the MODULE_STATE_LIVE, try_module_get() is not what
we wanted, plus module_is_live () checks if it is !GOING. Anyway, I don't
think this is needed any more for individual fcoe transport driver, e.g.,
fcoe.ko or bnx2fc, as the race is now for sysfs of libfcoe.

I will send out a patch to clean up the fcoe.c for this.

Thanks,
yi






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