Re: [PATCH v6 2/2] x86/MCE/AMD: Fix memory leak when `threshold_create_bank()` fails

[Ammar Faizi]

On 4/4/22 12:43 AM, Ammar Faizi wrote:
> On 4/4/22 12:03 AM, Thomas Gleixner wrote:
> > On Tue, Mar 29 2022 at 17:47, Ammar Faizi wrote:
> >
> > > In mce_threshold_create_device(), if threshold_create_bank() fails, the
> > > @bp will be leaked, because the call to mce_threshold_remove_device()
> > > will not free the @bp. mce_threshold_remove_device() frees
> > > @threshold_banks. At that point, the @bp has not been written to
> > > @threshold_banks, @threshold_banks is NULL, so the call is just a nop.
> > >
> > > Fix this by extracting the cleanup part into a new static function
> > > __threshold_remove_device(), then call it from create/remove device
> > > functions.
> >
> > The way simpler fix is to move
> >
> > >       }
> > >       this_cpu_write(threshold_banks, bp);
> >
> > before the loop. That's safe because the banks cannot yet be reached via
> > an MCE as the vector is not yet enabled:
> > >       if (thresholding_irq_en)
> > >           mce_threshold_vector = amd_threshold_interrupt;
> Thomas,
>
> I did like what you said (in the patch v4), but after Yazen and Borislav
> reviewed it, we got a conclusion that it's not safe.
>
> See [1] and [2] for the full message.
>
> [1]: https://lore.kernel.org/lkml/YkFsQhpGGXIFTMyp@xxxxxxx/
> [2]: https://lore.kernel.org/lkml/Yh+oyD%2F5M3TW5ZMM@yaz-ubuntu/
>
> Yazen, Borislav, please take a deeper look on this again. I will send
> a v7 revision to really make it simpler by moving that "per-CPU var write"
> before the loop.

(only if it's really safe)

--
Ammar Faizi