linux-kernel - Re: [PATCH] x86/MCE/AMD: Decrement threshold_bank refcount when removing threshold blocks

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Date:   Sat, 13 Aug 2022 12:09:52 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Mateusz Jończyk <mat.jonczyk@...pl>
Cc:     Yazen Ghannam <yazen.ghannam@....com>, linux-edac@...r.kernel.org,
        linux-kernel@...r.kernel.org, tony.luck@...el.com, x86@...nel.org,
        Smita.KoralahalliChannabasappa@....com, mpatocka@...hat.com,
        gregkh@...uxfoundation.org
Subject: Re: [PATCH] x86/MCE/AMD: Decrement threshold_bank refcount when
 removing threshold blocks

On Fri, Aug 12, 2022 at 11:14:44PM +0200, Mateusz Jończyk wrote:
> Shouldn't there be "kobject_put(&pos->kobj)" here instead?

Yes, it should.

> Also, it seems to me that "kobject_put(b->kobj);" before the loop
> may be relocated after the loop - so that the refcounts on the child
> objects are decreased first, then the refcount on the parent object.

Yes, I guess we can do that.

> Additionally, shouldn't there be a call to
> "kobject_put(&b->blocks->kobj);" in __threshold_remove_blocks()?

Makes sense, we do

	kobject_add(&b->blocks->kobj, ...

in __threshold_add_blocks().

> From what I understand, b->blocks is a list head, so we need to
> decrease the refcount on it too.

Not list_heads - we modify the refcount of kobjects. See what the arg of
kobject_put() is.

> After these changes, the __threshold_remove_blocks() function looks
> very similar to deallocate_threshold_blocks() function just above it.

Yes, minus the list_del(&pos->miscj); But that can be made conditional
with a bool arg to deallocate_threshold_blocks() and then remove
__threshold_remove_blocks().

Care to take Yazen's patch, fix it up, test it thoroughly (you should
enable KASAN to catch any potential memory leaks) and send it?

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette