linux-kernel - Re: [PATCH] Raise maximum number of memory controllers

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Date:   Tue, 25 Sep 2018 20:07:33 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     "Luck, Tony" <tony.luck@...el.com>
Cc:     Justin Ernst <justin.ernst@....com>, russ.anderson@....com,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        linux-edac@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Raise maximum number of memory controllers

On Tue, Sep 25, 2018 at 10:50:23AM -0700, Luck, Tony wrote:
> There are way too many places where we use the identifier "bus"
> in the edac core and drivers. But I'm not sure that we need a
> static array mc_bus[EDAC_MAX_MCS].

That, of course, is another way of looking at it which I didn't think
of.

> Why can't we:
> 
> 
> -	mci->bus = &mc_bus[mci->mc_idx];
> +	mci->bus = kmalloc(sizeof *(mci->bus), GFP_KERNEL);
> 
> and then figure out where to kfree(mci->bus) on driver removal?

AFAICT, in _edac_mc_free(). We free there mci itself so kfree(mci->bus)
can happen directly before it.

> Do we every do arithmetic on different mci->bus pointers that
> assume they are all part of a single array?

AFAICT, we use that thing for the bus_reg/unreg functions and we hand it
back'n'forth in edac_mc_sysfs.c, see

$ git grep -E "mci.*bus" drivers/edac/
drivers/edac/edac_mc.c:763:     mci->bus = &mc_bus[mci->mc_idx];
drivers/edac/edac_mc_sysfs.c:408:       csrow->dev.bus = mci->bus;
drivers/edac/edac_mc_sysfs.c:639:       dimm->dev.bus = mci->bus;
drivers/edac/edac_mc_sysfs.c:928:       mci->bus->name = name;
drivers/edac/edac_mc_sysfs.c:930:       edac_dbg(0, "creating bus %s\n", mci->bus->name);
drivers/edac/edac_mc_sysfs.c:932:       err = bus_register(mci->bus);
drivers/edac/edac_mc_sysfs.c:943:       mci->dev.bus = mci->bus;
drivers/edac/edac_mc_sysfs.c:1002:      bus_unregister(mci->bus);
drivers/edac/edac_mc_sysfs.c:1035:      struct bus_type *bus = mci->bus;
drivers/edac/edac_mc_sysfs.c:1036:      const char *name = mci->bus->name;
drivers/edac/edac_mc_sysfs.c:1071:      mci_pdev->bus = edac_get_sysfs_subsys();
drivers/edac/i5100_edac.c:967:  priv->debugfs = edac_debugfs_create_dir_at(mci->bus->name, i5100_debugfs);
drivers/edac/i7core_edac.c:1170:        pvt->addrmatch_dev->bus = mci->dev.bus;
drivers/edac/i7core_edac.c:1191:                pvt->chancounts_dev->bus = mci->dev.bus;

HOWEVER, look at

  88d84ac97378 ("EDAC: Fix lockdep splat")

Now I remember. I did that for lockdep because it wants statically
allocated memory. I'll try to think of something tomorrow.

Thx.

-- 
Regards/Gruss,
    Boris.

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