linux-kernel - Re: [PATCH v6 2/2] x86/MCE/AMD: Fix memory leak when `threshold_create

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Date:   Sun, 03 Apr 2022 19:03:58 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Ammar Faizi <ammarfaizi2@...weeb.org>,
        Borislav Petkov <bp@...en8.de>
Cc:     Ammar Faizi <ammarfaizi2@...weeb.org>,
        Alviro Iskandar Setiawan <alviro.iskandar@...weeb.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
        Tony Luck <tony.luck@...el.com>,
        Yazen Ghannam <yazen.ghannam@....com>,
        Linux Edac Mailing List <linux-edac@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Stable Kernel <stable@...r.kernel.org>,
        GNU/Weeb Mailing List <gwml@...r.gnuweeb.org>,
        x86 Mailing List <x86@...nel.org>
Subject: Re: [PATCH v6 2/2] x86/MCE/AMD: Fix memory leak when
 `threshold_create_bank()` fails

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;

Thanks,

        tglx